Utils: Add std::expected implementation

Adds a std::expected implementation that is compatible with >= C++11.

FilePath::fileContents and FilePath::writeFileContents as well as
FilePath::copyFile are changed to return std::expected.

A couple of macros have been added to aid in using the expected types.

An auto test was added showing how to use the library.

Change-Id: Ibe3aecfc1029a0cf13b45bf5184ff03a04a2393b
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

README.md

@@ -688,3 +688,15 @@ SQLite (https://www.sqlite.org) is in the Public Domain.
   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   SOFTWARE.
+
+### TartanLlama/expected
+
+  Implementation of std::expected compatible with C++11/C++14/C++17.
+
+  https://github.com/TartanLlama/expected
+
+  To the extent possible under law, the author(s) have dedicated all
+  copyright and related and neighboring rights to this software to the
+  public domain worldwide. This software is distributed without any warranty.
+
+  http://creativecommons.org/publicdomain/zero/1.0/

doc/qtcreator/src/overview/creator-acknowledgements.qdoc

@@ -988,5 +988,19 @@
         SOFTWARE.
         \endcode
 
+        \li \b TartanLlama/expected
+
+        Implementation of std::expected compatible with C++11/C++14/C++17.
+
+        The sources can be found in:
+        \list
+            \li \c QtCreator/src/libs/3rdparty/tl_expected
+            \li \l https://github.com/TartanLlama/expected
+        \endlist
+
+        CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
+
+        https://creativecommons.org/publicdomain/zero/1.0/
+
      \endlist
 */

src/libs/3rdparty/tl_expected/COPYING

@@ -0,0 +1,121 @@
+Creative Commons Legal Code
+
+CC0 1.0 Universal
+
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+
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+
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src/libs/3rdparty/tl_expected/README.md

@@ -0,0 +1,74 @@
+# expected
+Single header implementation of `std::expected` with functional-style extensions.
+
+[![Documentation Status](https://readthedocs.org/projects/tl-docs/badge/?version=latest)](https://tl.tartanllama.xyz/en/latest/?badge=latest)
+Clang + GCC: [![Linux Build Status](https://github.com/TartanLlama/expected/actions/workflows/cmake.yml/badge.svg)](https://github.com/TartanLlama/expected/actions/workflows/cmake.yml)
+MSVC: [![Windows Build Status](https://ci.appveyor.com/api/projects/status/k5x00xa11y3s5wsg?svg=true)](https://ci.appveyor.com/project/TartanLlama/expected)
+
+Available on [Vcpkg](https://github.com/microsoft/vcpkg/tree/master/ports/tl-expected) and [Conan](https://github.com/yipdw/conan-tl-expected).
+
+[`std::expected`](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0323r3.pdf) is proposed as the preferred way to represent object which will either have an expected value, or an unexpected value giving information about why something failed. Unfortunately, chaining together many computations which may fail can be verbose, as error-checking code will be mixed in with the actual programming logic. This implementation provides a number of utilities to make coding with `expected` cleaner.
+
+For example, instead of writing this code:
+
+```cpp
+std::expected<image,fail_reason> get_cute_cat (const image& img) {
+    auto cropped = crop_to_cat(img);
+    if (!cropped) {
+      return cropped;
+    }
+
+    auto with_tie = add_bow_tie(*cropped);
+    if (!with_tie) {
+      return with_tie;
+    }
+
+    auto with_sparkles = make_eyes_sparkle(*with_tie);
+    if (!with_sparkles) {
+       return with_sparkles;
+    }
+
+    return add_rainbow(make_smaller(*with_sparkles));
+}
+```
+
+You can do this:
+
+```cpp
+tl::expected<image,fail_reason> get_cute_cat (const image& img) {
+    return crop_to_cat(img)
+           .and_then(add_bow_tie)
+           .and_then(make_eyes_sparkle)
+           .map(make_smaller)
+           .map(add_rainbow);
+}
+```
+
+The interface is the same as `std::expected` as proposed in [p0323r3](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0323r3.pdf), but the following member functions are also defined. Explicit types are for clarity.
+
+- `map`: carries out some operation on the stored object if there is one.
+  * `tl::expected<std::size_t,std::error_code> s = exp_string.map(&std::string::size);`
+- `map_error`: carries out some operation on the unexpected object if there is one.
+  * `my_error_code translate_error (std::error_code);`
+  * `tl::expected<int,my_error_code> s = exp_int.map_error(translate_error);`
+- `and_then`: like `map`, but for operations which return a `tl::expected`.
+  * `tl::expected<ast, fail_reason> parse (const std::string& s);`
+  * `tl::expected<ast, fail_reason> exp_ast = exp_string.and_then(parse);`
+- `or_else`: calls some function if there is no value stored.
+  * `exp.or_else([] { throw std::runtime_error{"oh no"}; });`
+
+### Compiler support
+
+Tested on:
+
+- Linux
+  * clang++ 3.5, 3.6, 3.7, 3.8, 3.9, 4, 5, 6, 7, 8, 9, 10, 11
+  * g++ 4.8, 4.9, 5.5, 6.4, 7.5, 8, 9, 10 
+- Windows
+  * MSVC 2015, 2017, 2019, 2022
+
+----------
+
+[![CC0](http://i.creativecommons.org/p/zero/1.0/88x31.png)]("http://creativecommons.org/publicdomain/zero/1.0/")
+
+To the extent possible under law, [Sy Brand](https://twitter.com/TartanLlama) has waived all copyright and related or neighboring rights to the `expected` library. This work is published from: United Kingdom.

src/libs/qmljs/qmljsmodelmanagerinterface.cpp

@@ -875,7 +875,7 @@ static bool findNewQmlLibraryInPath(const Utils::FilePath &path,
     }
 
     // found a new library!
-    const std::optional<QByteArray> contents = qmldirFile.fileContents();
+    const expected_str<QByteArray> contents = qmldirFile.fileContents();
     if (!contents)
         return false;
     QString qmldirData = QString::fromUtf8(*contents);
@@ -985,7 +985,7 @@ void ModelManagerInterface::parseLoop(QSet<Utils::FilePath> &scannedPaths,
             contents = entry.first;
             documentRevision = entry.second;
         } else {
-            const std::optional<QByteArray> fileContents = fileName.fileContents();
+            const expected_str<QByteArray> fileContents = fileName.fileContents();
             if (fileContents) {
                 QTextStream ins(*fileContents);
                 contents = ins.readAll();

src/libs/utils/CMakeLists.txt

@@ -42,6 +42,7 @@ add_qtc_library(Utils
     environmentmodel.cpp environmentmodel.h
     execmenu.cpp execmenu.h
     executeondestruction.h
+    expected.h
     fadingindicator.cpp fadingindicator.h
     faketooltip.cpp faketooltip.h
     fancylineedit.cpp fancylineedit.h

src/libs/utils/devicefileaccess.cpp

@@ -6,8 +6,10 @@
 #include "algorithm.h"
 #include "commandline.h"
 #include "environment.h"
+#include "expected.h"
 #include "hostosinfo.h"
 #include "qtcassert.h"
+#include "utilstr.h"
 
 #include <QCoreApplication>
 #include <QOperatingSystemVersion>
@@ -18,8 +20,8 @@
 #ifdef QTCREATOR_PCH_H
 #define CALLBACK WINAPI
 #endif
-#include <qt_windows.h>
 #include <shlobj.h>
+#include <qt_windows.h>
 #else
 #include <qplatformdefs.h>
 #endif
@@ -137,12 +139,13 @@ bool DeviceFileAccess::removeRecursively(const FilePath &filePath, QString *erro
     return false;
 }
 
-bool DeviceFileAccess::copyFile(const FilePath &filePath, const FilePath &target) const
+expected_str<void> DeviceFileAccess::copyFile(const FilePath &filePath, const FilePath &target) const
 {
     Q_UNUSED(filePath)
     Q_UNUSED(target)
     QTC_CHECK(false);
-    return false;
+    return make_unexpected(
+        Tr::tr("copyFile is not implemented for \"%1\"").arg(filePath.toUserOutput()));
 }
 
 bool DeviceFileAccess::renameFile(const FilePath &filePath, const FilePath &target) const
@@ -166,8 +169,7 @@ FilePath DeviceFileAccess::symLinkTarget(const FilePath &filePath) const
     return {};
 }
 
-void DeviceFileAccess::iterateDirectory(
+void DeviceFileAccess::iterateDirectory(const FilePath &filePath,
-        const FilePath &filePath,
                                         const FilePath::IterateDirCallback &callBack,
                                         const FileFilter &filter) const
 {
@@ -177,8 +179,7 @@ void DeviceFileAccess::iterateDirectory(
     QTC_CHECK(false);
 }
 
-std::optional<QByteArray> DeviceFileAccess::fileContents(
+expected_str<QByteArray> DeviceFileAccess::fileContents(const FilePath &filePath,
-        const FilePath &filePath,
                                                         qint64 limit,
                                                         qint64 offset) const
 {
@@ -186,11 +187,11 @@ std::optional<QByteArray> DeviceFileAccess::fileContents(
     Q_UNUSED(limit)
     Q_UNUSED(offset)
     QTC_CHECK(false);
-    return {};
+    return make_unexpected(
+        Tr::tr("fileContents is not implemented for \"%1\"").arg(filePath.toUserOutput()));
 }
 
-bool DeviceFileAccess::writeFileContents(
+expected_str<qint64> DeviceFileAccess::writeFileContents(const FilePath &filePath,
-        const FilePath &filePath,
                                                          const QByteArray &data,
                                                          qint64 offset) const
 {
@@ -198,7 +199,8 @@ bool DeviceFileAccess::writeFileContents(
     Q_UNUSED(data)
     Q_UNUSED(offset)
     QTC_CHECK(false);
-    return false;
+    return make_unexpected(
+        Tr::tr("writeFileContents is not implemented for \"%1\"").arg(filePath.toUserOutput()));
 }
 
 FilePathInfo DeviceFileAccess::filePathInfo(const FilePath &filePath) const
@@ -251,8 +253,7 @@ QByteArray DeviceFileAccess::fileId(const FilePath &filePath) const
 }
 
 std::optional<FilePath> DeviceFileAccess::refersToExecutableFile(
-        const FilePath &filePath,
+    const FilePath &filePath, FilePath::MatchScope matchScope) const
-        FilePath::MatchScope matchScope) const
 {
     Q_UNUSED(matchScope)
     if (isExecutableFile(filePath))
@@ -260,33 +261,29 @@ std::optional<FilePath> DeviceFileAccess::refersToExecutableFile(
     return {};
 }
 
-void DeviceFileAccess::asyncFileContents(
+void DeviceFileAccess::asyncFileContents(const FilePath &filePath,
-        const FilePath &filePath,
+                                         const Continuation<expected_str<QByteArray>> &cont,
-        const Continuation<std::optional<QByteArray>> &cont,
                                          qint64 limit,
                                          qint64 offset) const
 {
     cont(fileContents(filePath, limit, offset));
 }
 
-void DeviceFileAccess::asyncWriteFileContents(
+void DeviceFileAccess::asyncWriteFileContents(const FilePath &filePath,
-        const FilePath &filePath,
+                                              const Continuation<expected_str<qint64>> &cont,
-        const Continuation<bool> &cont,
                                               const QByteArray &data,
                                               qint64 offset) const
 {
     cont(writeFileContents(filePath, data, offset));
 }
 
-void DeviceFileAccess::asyncCopyFile(
+void DeviceFileAccess::asyncCopyFile(const FilePath &filePath,
-        const FilePath &filePath,
+                                     const Continuation<expected_str<void>> &cont,
-        const Continuation<bool> &cont,
                                      const FilePath &target) const
 {
     cont(copyFile(filePath, target));
 }
 
-
 // DesktopDeviceFileAccess
 
 DesktopDeviceFileAccess::~DesktopDeviceFileAccess() = default;
@@ -303,8 +300,8 @@ bool DesktopDeviceFileAccess::isExecutableFile(const FilePath &filePath) const
     return fi.isExecutable() && !fi.isDir();
 }
 
-static std::optional<FilePath> isWindowsExecutableHelper
+static std::optional<FilePath> isWindowsExecutableHelper(const FilePath &filePath,
-    (const FilePath &filePath, const QStringView suffix)
+                                                         const QStringView suffix)
 {
     const QFileInfo fi(filePath.path().append(suffix));
     if (!fi.isExecutable() || fi.isDir())
@@ -314,8 +311,7 @@ static std::optional<FilePath> isWindowsExecutableHelper
 }
 
 std::optional<FilePath> DesktopDeviceFileAccess::refersToExecutableFile(
-        const FilePath &filePath,
+    const FilePath &filePath, FilePath::MatchScope matchScope) const
-        FilePath::MatchScope matchScope) const
 {
     if (isExecutableFile(filePath))
         return filePath;
@@ -444,15 +440,16 @@ bool DesktopDeviceFileAccess::removeRecursively(const FilePath &filePath, QStrin
             return false;
         }
 
-        const QStringList fileNames = dir.entryList(
+        const QStringList fileNames = dir.entryList(QDir::Files | QDir::Hidden | QDir::System
-                    QDir::Files | QDir::Hidden | QDir::System | QDir::Dirs | QDir::NoDotAndDotDot);
+                                                    | QDir::Dirs | QDir::NoDotAndDotDot);
         for (const QString &fileName : fileNames) {
             if (!removeRecursively(filePath / fileName, error))
                 return false;
         }
         if (!QDir::root().rmdir(dir.path())) {
             if (error) {
-                *error = QCoreApplication::translate("Utils::FileUtils", "Failed to remove directory \"%1\".")
+                *error = QCoreApplication::translate("Utils::FileUtils",
+                                                     "Failed to remove directory \"%1\".")
                              .arg(filePath.toUserOutput());
             }
             return false;
@@ -460,7 +457,8 @@ bool DesktopDeviceFileAccess::removeRecursively(const FilePath &filePath, QStrin
     } else {
         if (!QFile::remove(filePath.path())) {
             if (error) {
-                *error = QCoreApplication::translate("Utils::FileUtils", "Failed to remove file \"%1\".")
+                *error = QCoreApplication::translate("Utils::FileUtils",
+                                                     "Failed to remove file \"%1\".")
                              .arg(filePath.toUserOutput());
             }
             return false;
@@ -469,9 +467,14 @@ bool DesktopDeviceFileAccess::removeRecursively(const FilePath &filePath, QStrin
     return true;
 }
 
-bool DesktopDeviceFileAccess::copyFile(const FilePath &filePath, const FilePath &target) const
+expected_str<void> DesktopDeviceFileAccess::copyFile(const FilePath &filePath,
+                                                     const FilePath &target) const
 {
-    return QFile::copy(filePath.path(), target.path());
+    if (QFile::copy(filePath.path(), target.path()))
+        return {};
+    return make_unexpected(Tr::tr("Failed to copy file \"%1\" to \"%2\".")
+                               .arg(filePath.toUserOutput())
+                               .arg(target.toUserOutput()));
 }
 
 bool DesktopDeviceFileAccess::renameFile(const FilePath &filePath, const FilePath &target) const
@@ -514,8 +517,7 @@ FilePath DesktopDeviceFileAccess::symLinkTarget(const FilePath &filePath) const
     return FilePath::fromString(info.symLinkTarget());
 }
 
-void DesktopDeviceFileAccess::iterateDirectory(
+void DesktopDeviceFileAccess::iterateDirectory(const FilePath &filePath,
-        const FilePath &filePath,
                                                const FilePath::IterateDirCallback &callBack,
                                                const FileFilter &filter) const
 {
@@ -532,18 +534,17 @@ void DesktopDeviceFileAccess::iterateDirectory(
     }
 }
 
-std::optional<QByteArray> DesktopDeviceFileAccess::fileContents(
+expected_str<QByteArray> DesktopDeviceFileAccess::fileContents(const FilePath &filePath,
-        const FilePath &filePath,
                                                                qint64 limit,
                                                                qint64 offset) const
 {
     const QString path = filePath.path();
     QFile f(path);
     if (!f.exists())
-        return {};
+        return make_unexpected(Tr::tr("File \"%1\" does not exist").arg(path));
 
     if (!f.open(QFile::ReadOnly))
-        return {};
+        return make_unexpected(Tr::tr("Could not open File \"%1\"").arg(path));
 
     if (offset != 0)
         f.seek(offset);
@@ -551,21 +552,35 @@ std::optional<QByteArray> DesktopDeviceFileAccess::fileContents(
     if (limit != -1)
         return f.read(limit);
 
-    return f.readAll();
+    const QByteArray data = f.readAll();
+    if (f.error() != QFile::NoError) {
+        return make_unexpected(
+            Tr::tr("Cannot read \"%1\": %2").arg(filePath.toUserOutput(), f.errorString()));
+    }
+
+    return data;
 }
 
-bool DesktopDeviceFileAccess::writeFileContents(
+expected_str<qint64> DesktopDeviceFileAccess::writeFileContents(const FilePath &filePath,
-        const FilePath &filePath,
                                                                 const QByteArray &data,
                                                                 qint64 offset) const
 {
     QFile file(filePath.path());
     const bool isOpened = file.open(QFile::WriteOnly | QFile::Truncate);
-    QTC_ASSERT(isOpened, return false);
+    if (!isOpened)
+        return make_unexpected(
+            Tr::tr("Could not open file \"%1\" for writing").arg(filePath.toUserOutput()));
+
     if (offset != 0)
         file.seek(offset);
     qint64 res = file.write(data);
-    return res == data.size();
+    if (res != data.size())
+        return make_unexpected(
+            Tr::tr("Could not write to file \"%1\" (only %2 of %3 bytes written)")
+                .arg(filePath.toUserOutput())
+                .arg(res)
+                .arg(data.size()));
+    return res;
 }
 
 QDateTime DesktopDeviceFileAccess::lastModified(const FilePath &filePath) const
@@ -603,7 +618,9 @@ static inline QByteArray fileIdWin7(HANDLE handle)
     BY_HANDLE_FILE_INFORMATION info;
     if (GetFileInformationByHandle(handle, &info)) {
         char buffer[sizeof "01234567:0123456701234567\0"];
-        qsnprintf(buffer, sizeof(buffer), "%lx:%08lx%08lx",
+        qsnprintf(buffer,
+                  sizeof(buffer),
+                  "%lx:%08lx%08lx",
                   info.dwVolumeSerialNumber,
                   info.nFileIndexHigh,
                   info.nFileIndexLow);
@@ -618,20 +635,25 @@ static QByteArray fileIdWin8(HANDLE handle)
     QByteArray result;
     FILE_ID_INFO infoEx;
     if (GetFileInformationByHandleEx(handle,
-                                     static_cast<FILE_INFO_BY_HANDLE_CLASS>(18), // FileIdInfo in Windows 8
+                                     static_cast<FILE_INFO_BY_HANDLE_CLASS>(
-                                     &infoEx, sizeof(FILE_ID_INFO))) {
+                                         18), // FileIdInfo in Windows 8
+                                     &infoEx,
+                                     sizeof(FILE_ID_INFO))) {
         result = QByteArray::number(infoEx.VolumeSerialNumber, 16);
         result += ':';
         // Note: MinGW-64's definition of FILE_ID_128 differs from the MSVC one.
-        result += QByteArray(reinterpret_cast<const char *>(&infoEx.FileId), int(sizeof(infoEx.FileId))).toHex();
+        result += QByteArray(reinterpret_cast<const char *>(&infoEx.FileId),
+                             int(sizeof(infoEx.FileId)))
+                      .toHex();
     }
     return result;
 }
 
 static QByteArray fileIdWin(HANDLE fHandle)
 {
-    return QOperatingSystemVersion::current() >= QOperatingSystemVersion::Windows8 ?
+    return QOperatingSystemVersion::current() >= QOperatingSystemVersion::Windows8
-                fileIdWin8(HANDLE(fHandle)) : fileIdWin7(HANDLE(fHandle));
+               ? fileIdWin8(HANDLE(fHandle))
+               : fileIdWin7(HANDLE(fHandle));
 }
 #endif
 
@@ -640,10 +662,13 @@ QByteArray DesktopDeviceFileAccess::fileId(const FilePath &filePath) const
     QByteArray result;
 
 #ifdef Q_OS_WIN
-    const HANDLE handle =
+    const HANDLE handle = CreateFile((wchar_t *) filePath.toUserOutput().utf16(),
-            CreateFile((wchar_t*)filePath.toUserOutput().utf16(), 0,
+                                     0,
-                       FILE_SHARE_READ, NULL, OPEN_EXISTING,
+                                     FILE_SHARE_READ,
-                       FILE_FLAG_BACKUP_SEMANTICS, NULL);
+                                     NULL,
+                                     OPEN_EXISTING,
+                                     FILE_FLAG_BACKUP_SEMANTICS,
+                                     NULL);
     if (handle != INVALID_HANDLE_VALUE) {
         result = fileIdWin(handle);
         CloseHandle(handle);
@@ -668,7 +693,6 @@ OsType DesktopDeviceFileAccess::osType(const FilePath &filePath) const
     return HostOsInfo::hostOs();
 }
 
-
 // UnixDeviceAccess
 
 UnixDeviceFileAccess::~UnixDeviceFileAccess() = default;
@@ -769,9 +793,19 @@ bool UnixDeviceFileAccess::removeRecursively(const FilePath &filePath, QString *
     return result.exitCode == 0;
 }
 
-bool UnixDeviceFileAccess::copyFile(const FilePath &filePath, const FilePath &target) const
+expected_str<void> UnixDeviceFileAccess::copyFile(const FilePath &filePath,
+                                                  const FilePath &target) const
 {
-    return runInShellSuccess({"cp", {filePath.path(), target.path()}, OsType::OsTypeLinux});
+    const RunResult result = runInShell(
+        {"cp", {filePath.path(), target.path()}, OsType::OsTypeLinux});
+
+    if (result.exitCode != 0) {
+        return make_unexpected(Tr::tr("Failed to copy file \"%1\" to \"%2\": %3")
+                                   .arg(filePath.toUserOutput())
+                                   .arg(target.toUserOutput())
+                                   .arg(QString::fromUtf8(result.stdErr)));
+    }
+    return {};
 }
 
 bool UnixDeviceFileAccess::renameFile(const FilePath &filePath, const FilePath &target) const
@@ -781,13 +815,13 @@ bool UnixDeviceFileAccess::renameFile(const FilePath &filePath, const FilePath &
 
 FilePath UnixDeviceFileAccess::symLinkTarget(const FilePath &filePath) const
 {
-    const RunResult result = runInShell({"readlink", {"-n", "-e", filePath.path()}, OsType::OsTypeLinux});
+    const RunResult result = runInShell(
+        {"readlink", {"-n", "-e", filePath.path()}, OsType::OsTypeLinux});
     const QString out = QString::fromUtf8(result.stdOut);
     return out.isEmpty() ? FilePath() : filePath.withNewPath(out);
 }
 
-std::optional<QByteArray> UnixDeviceFileAccess::fileContents(
+expected_str<QByteArray> UnixDeviceFileAccess::fileContents(const FilePath &filePath,
-        const FilePath &filePath,
                                                             qint64 limit,
                                                             qint64 offset) const
 {
@@ -802,13 +836,14 @@ std::optional<QByteArray> UnixDeviceFileAccess::fileContents(
     const RunResult r = runInShell({"dd", args, OsType::OsTypeLinux});
 
     if (r.exitCode != 0)
-        return {};
+        return make_unexpected(Tr::tr("Failed reading file \"%1\": %2")
+                                   .arg(filePath.toUserOutput())
+                                   .arg(QString::fromUtf8(r.stdErr)));
 
     return r.stdOut;
 }
 
-bool UnixDeviceFileAccess::writeFileContents(
+expected_str<qint64> UnixDeviceFileAccess::writeFileContents(const FilePath &filePath,
-        const FilePath &filePath,
                                                              const QByteArray &data,
                                                              qint64 offset) const
 {
@@ -817,7 +852,14 @@ bool UnixDeviceFileAccess::writeFileContents(
         args.append("bs=1");
         args.append(QString("seek=%1").arg(offset));
     }
-    return runInShellSuccess({"dd", args, OsType::OsTypeLinux}, data);
+    RunResult result = runInShell({"dd", args, OsType::OsTypeLinux}, data);
+
+    if (result.exitCode != 0) {
+        return make_unexpected(Tr::tr("Failed writing file \"%1\": %2")
+                                   .arg(filePath.toUserOutput())
+                                   .arg(QString::fromUtf8(result.stdErr)));
+    }
+    return data.size();
 }
 
 OsType UnixDeviceFileAccess::osType(const FilePath &filePath) const
@@ -828,7 +870,8 @@ OsType UnixDeviceFileAccess::osType(const FilePath &filePath) const
 
 QDateTime UnixDeviceFileAccess::lastModified(const FilePath &filePath) const
 {
-    const RunResult result = runInShell({"stat", {"-L", "-c", "%Y", filePath.path()}, OsType::OsTypeLinux});
+    const RunResult result = runInShell(
+        {"stat", {"-L", "-c", "%Y", filePath.path()}, OsType::OsTypeLinux});
     qint64 secs = result.stdOut.toLongLong();
     const QDateTime dt = QDateTime::fromSecsSinceEpoch(secs, Qt::UTC);
     return dt;
@@ -836,10 +879,13 @@ QDateTime UnixDeviceFileAccess::lastModified(const FilePath &filePath) const
 
 QFile::Permissions UnixDeviceFileAccess::permissions(const FilePath &filePath) const
 {
-    const RunResult result = runInShell({"stat", {"-L", "-c", "%a", filePath.path()}, OsType::OsTypeLinux});
+    const RunResult result = runInShell(
+        {"stat", {"-L", "-c", "%a", filePath.path()}, OsType::OsTypeLinux});
     const uint bits = result.stdOut.toUInt(nullptr, 8);
     QFileDevice::Permissions perm = {};
-#define BIT(n, p) if (bits & (1<<n)) perm |= QFileDevice::p
+#define BIT(n, p) \
+    if (bits & (1 << n)) \
+    perm |= QFileDevice::p
     BIT(0, ExeOther);
     BIT(1, WriteOther);
     BIT(2, ReadOther);
@@ -856,12 +902,14 @@ QFile::Permissions UnixDeviceFileAccess::permissions(const FilePath &filePath) c
 bool UnixDeviceFileAccess::setPermissions(const FilePath &filePath, QFile::Permissions perms) const
 {
     const int flags = int(perms);
-    return runInShellSuccess({"chmod", {QString::number(flags, 16), filePath.path()}, OsType::OsTypeLinux});
+    return runInShellSuccess(
+        {"chmod", {QString::number(flags, 16), filePath.path()}, OsType::OsTypeLinux});
 }
 
 qint64 UnixDeviceFileAccess::fileSize(const FilePath &filePath) const
 {
-    const RunResult result = runInShell({"stat", {"-L", "-c", "%s", filePath.path()}, OsType::OsTypeLinux});
+    const RunResult result = runInShell(
+        {"stat", {"-L", "-c", "%s", filePath.path()}, OsType::OsTypeLinux});
     return result.stdOut.toLongLong();
 }
 
@@ -873,7 +921,8 @@ qint64 UnixDeviceFileAccess::bytesAvailable(const FilePath &filePath) const
 
 QByteArray UnixDeviceFileAccess::fileId(const FilePath &filePath) const
 {
-    const RunResult result = runInShell({"stat", {"-L", "-c", "%D:%i", filePath.path()}, OsType::OsTypeLinux});
+    const RunResult result = runInShell(
+        {"stat", {"-L", "-c", "%D:%i", filePath.path()}, OsType::OsTypeLinux});
     if (result.exitCode != 0)
         return {};
 
@@ -882,13 +931,13 @@ QByteArray UnixDeviceFileAccess::fileId(const FilePath &filePath) const
 
 FilePathInfo UnixDeviceFileAccess::filePathInfo(const FilePath &filePath) const
 {
-    const RunResult stat = runInShell({"stat", {"-L", "-c", "%f %Y %s", filePath.path()}, OsType::OsTypeLinux});
+    const RunResult stat = runInShell(
+        {"stat", {"-L", "-c", "%f %Y %s", filePath.path()}, OsType::OsTypeLinux});
     return FileUtils::filePathInfoFromTriple(QString::fromLatin1(stat.stdOut));
 }
 
 // returns whether 'find' could be used.
-bool UnixDeviceFileAccess::iterateWithFind(
+bool UnixDeviceFileAccess::iterateWithFind(const FilePath &filePath,
-        const FilePath &filePath,
                                            const FileFilter &filter,
                                            const FilePath::IterateDirCallback &callBack) const
 {
@@ -899,7 +948,8 @@ bool UnixDeviceFileAccess::iterateWithFind(
     // TODO: Using stat -L will always return the link target, not the link itself.
     // We may wan't to add the information that it is a link at some point.
     if (callBack.index() == 1)
-        cmdLine.addArgs(R"(-exec echo -n \"{}\"" " \; -exec stat -L -c "%f %Y %s" "{}" \;)", CommandLine::Raw);
+        cmdLine.addArgs(R"(-exec echo -n \"{}\"" " \; -exec stat -L -c "%f %Y %s" "{}" \;)",
+                        CommandLine::Raw);
 
     const RunResult result = runInShell(cmdLine);
     const QString out = QString::fromUtf8(result.stdOut);
@@ -951,8 +1001,7 @@ bool UnixDeviceFileAccess::iterateWithFind(
     return true;
 }
 
-void UnixDeviceFileAccess::findUsingLs(
+void UnixDeviceFileAccess::findUsingLs(const QString &current,
-        const QString &current,
                                        const FileFilter &filter,
                                        QStringList *found) const
 {
@@ -975,8 +1024,8 @@ static void iterateLsOutput(const FilePath &base,
                             const FileFilter &filter,
                             const FilePath::IterateDirCallback &callBack)
 {
-    const QList<QRegularExpression> nameRegexps =
+    const QList<QRegularExpression> nameRegexps
-            transform(filter.nameFilters, [](const QString &filter) {
+        = transform(filter.nameFilters, [](const QString &filter) {
               QRegularExpression re;
               re.setPattern(QRegularExpression::wildcardToRegularExpression(filter));
               QTC_CHECK(re.isValid());
@@ -1009,8 +1058,7 @@ static void iterateLsOutput(const FilePath &base,
     }
 }
 
-void UnixDeviceFileAccess::iterateDirectory(
+void UnixDeviceFileAccess::iterateDirectory(const FilePath &filePath,
-        const FilePath &filePath,
                                             const FilePath::IterateDirCallback &callBack,
                                             const FileFilter &filter) const
 {
@@ -1019,7 +1067,8 @@ void UnixDeviceFileAccess::iterateDirectory(
     if (m_tryUseFind) {
         if (iterateWithFind(filePath, filter, callBack))
             return;
-        m_tryUseFind = false; // remember the failure for the next time and use the 'ls' fallback below.
+        m_tryUseFind
+            = false; // remember the failure for the next time and use the 'ls' fallback below.
     }
 
     // if we do not have find - use ls as fallback
@@ -1028,4 +1077,4 @@ void UnixDeviceFileAccess::iterateDirectory(
     iterateLsOutput(filePath, entries, filter, callBack);
 }
 
-} // Utils
+} // namespace Utils

src/libs/utils/devicefileaccess.h

@@ -34,7 +34,7 @@ protected:
     virtual bool exists(const FilePath &filePath) const;
     virtual bool removeFile(const FilePath &filePath) const;
     virtual bool removeRecursively(const FilePath &filePath, QString *error) const;
-    virtual bool copyFile(const FilePath &filePath, const FilePath &target) const;
+    virtual expected_str<void> copyFile(const FilePath &filePath, const FilePath &target) const;
     virtual bool renameFile(const FilePath &filePath, const FilePath &target) const;
 
     virtual OsType osType(const FilePath &filePath) const;
@@ -56,30 +56,26 @@ protected:
             const FilePath::IterateDirCallback &callBack,
             const FileFilter &filter) const;
 
-    virtual std::optional<QByteArray> fileContents(
+    virtual expected_str<QByteArray> fileContents(const FilePath &filePath,
-            const FilePath &filePath,
-            qint64 limit,
-            qint64 offset) const;
-    virtual bool writeFileContents(
-            const FilePath &filePath,
-            const QByteArray &data,
-            qint64 offset) const;
-
-    virtual void asyncFileContents(
-            const FilePath &filePath,
-            const Continuation<std::optional<QByteArray>> &cont,
                                                   qint64 limit,
                                                   qint64 offset) const;
 
-    virtual void asyncWriteFileContents(
+    virtual expected_str<qint64> writeFileContents(const FilePath &filePath,
-            const FilePath &filePath,
-            const Continuation<bool> &cont,
                                                    const QByteArray &data,
                                                    qint64 offset) const;
 
-    virtual void asyncCopyFile(
+    virtual void asyncFileContents(const FilePath &filePath,
-            const FilePath &filePath,
+                                   const Continuation<expected_str<QByteArray>> &cont,
-            const Continuation<bool> &cont,
+                                   qint64 limit,
+                                   qint64 offset) const;
+
+    virtual void asyncWriteFileContents(const FilePath &filePath,
+                                        const Continuation<expected_str<qint64>> &cont,
+                                        const QByteArray &data,
+                                        qint64 offset) const;
+
+    virtual void asyncCopyFile(const FilePath &filePath,
+                               const Continuation<expected_str<void>> &cont,
                                const FilePath &target) const;
 };
 
@@ -105,7 +101,7 @@ protected:
     bool exists(const FilePath &filePath) const override;
     bool removeFile(const FilePath &filePath) const override;
     bool removeRecursively(const FilePath &filePath, QString *error) const override;
-    bool copyFile(const FilePath &filePath, const FilePath &target) const override;
+    expected_str<void> copyFile(const FilePath &filePath, const FilePath &target) const override;
     bool renameFile(const FilePath &filePath, const FilePath &target) const override;
 
     OsType osType(const FilePath &filePath) const override;
@@ -127,12 +123,10 @@ protected:
             const FilePath::IterateDirCallback &callBack,
             const FileFilter &filter) const override;
 
-    std::optional<QByteArray> fileContents(
+    expected_str<QByteArray> fileContents(const FilePath &filePath,
-            const FilePath &filePath,
                                           qint64 limit,
                                           qint64 offset) const override;
-    bool writeFileContents(
+    expected_str<qint64> writeFileContents(const FilePath &filePath,
-            const FilePath &filePath,
                                            const QByteArray &data,
                                            qint64 offset) const override;
 };
@@ -160,7 +154,7 @@ protected:
     bool exists(const FilePath &filePath) const override;
     bool removeFile(const FilePath &filePath) const override;
     bool removeRecursively(const FilePath &filePath, QString *error) const override;
-    bool copyFile(const FilePath &filePath, const FilePath &target) const override;
+    expected_str<void> copyFile(const FilePath &filePath, const FilePath &target) const override;
     bool renameFile(const FilePath &filePath, const FilePath &target) const override;
 
     FilePathInfo filePathInfo(const FilePath &filePath) const override;
@@ -178,12 +172,10 @@ protected:
             const FilePath::IterateDirCallback &callBack,
             const FileFilter &filter) const override;
 
-    std::optional<QByteArray> fileContents(
+    expected_str<QByteArray> fileContents(const FilePath &filePath,
-            const FilePath &filePath,
                                           qint64 limit,
                                           qint64 offset) const override;
-    bool writeFileContents(
+    expected_str<qint64> writeFileContents(const FilePath &filePath,
-            const FilePath &filePath,
                                            const QByteArray &data,
                                            qint64 offset) const override;
 

src/libs/utils/elfreader.cpp

@@ -3,6 +3,7 @@
 
 #include "elfreader.h"
 
+#include "expected.h"
 #include "qtcassert.h"
 
 #include <QDir>
@@ -85,7 +86,9 @@ ElfMapper::ElfMapper(const ElfReader *reader)
 bool ElfMapper::map()
 {
     if (binary.needsDevice()) {
-        raw = binary.fileContents().value_or(QByteArray());
+        const expected_str<QByteArray> contents = binary.fileContents();
+        QTC_CHECK(contents);
+        raw = contents.value_or(QByteArray());
         start = raw.constData();
         fdlen = raw.size();
         return fdlen > 0;

src/libs/utils/expected.h

@@ -0,0 +1,47 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0+ OR GPL-3.0 WITH Qt-GPL-exception-1.0
+
+#pragma once
+
+#include "qtcassert.h"
+
+#include "../3rdparty/tl_expected/include/tl/expected.hpp"
+
+namespace Utils {
+
+template<class T, class E>
+using expected = tl::expected<T, E>;
+
+template<class T>
+using expected_str = tl::expected<T, QString>;
+
+template<class E>
+using unexpected = tl::unexpected<E>;
+using unexpect_t = tl::unexpect_t;
+
+static constexpr unexpect_t unexpect{};
+
+template<class E>
+constexpr unexpected<std::decay_t<E>> make_unexpected(E &&e)
+{
+    return tl::make_unexpected(e);
+}
+
+} // namespace Utils
+
+//! If 'expected' has an error the error will be printed and the 'action' will be executed.
+#define QTC_ASSERT_EXPECTED(expected, action) \
+    { \
+        if (Q_LIKELY(expected)) { \
+        } else { \
+            ::Utils::writeAssertLocation(QString("%1:%2: %3") \
+                                             .arg(__FILE__) \
+                                             .arg(__LINE__) \
+                                             .arg(expected.error()) \
+                                             .toUtf8() \
+                                             .data()); \
+            action; \
+        } \
+        do { \
+        } while (0); \
+    }

src/libs/utils/filepath.cpp

@@ -9,15 +9,17 @@
 #include "fileutils.h"
 #include "hostosinfo.h"
 #include "qtcassert.h"
+#include "utilstr.h"
 
-#include <QtGlobal>
+#include <QByteArray>
 #include <QDateTime>
 #include <QDebug>
 #include <QDirIterator>
 #include <QFileInfo>
 #include <QRegularExpression>
-#include <QUrl>
 #include <QStringView>
+#include <QUrl>
+#include <QtGlobal>
 
 #ifdef Q_OS_WIN
 #ifdef QTCREATOR_PCH_H
@@ -494,7 +496,7 @@ void FilePath::iterateDirectories(const FilePaths &dirs,
         dir.iterateDirectory(callBack, filter);
 }
 
-std::optional<QByteArray> FilePath::fileContents(qint64 maxSize, qint64 offset) const
+expected_str<QByteArray> FilePath::fileContents(qint64 maxSize, qint64 offset) const
 {
     return fileAccess()->fileContents(*this, maxSize, offset);
 }
@@ -510,15 +512,14 @@ bool FilePath::ensureReachable(const FilePath &other) const
     return false;
 }
 
-void FilePath::asyncFileContents(
+void FilePath::asyncFileContents(const Continuation<const expected_str<QByteArray> &> &cont,
-        const Continuation<const std::optional<QByteArray> &> &cont,
                                  qint64 maxSize,
                                  qint64 offset) const
 {
     return fileAccess()->asyncFileContents(*this, cont, maxSize, offset);
 }
 
-bool FilePath::writeFileContents(const QByteArray &data, qint64 offset) const
+expected_str<qint64> FilePath::writeFileContents(const QByteArray &data, qint64 offset) const
 {
     return fileAccess()->writeFileContents(*this, data, offset);
 }
@@ -528,8 +529,7 @@ FilePathInfo FilePath::filePathInfo() const
     return fileAccess()->filePathInfo(*this);
 }
 
-void FilePath::asyncWriteFileContents(
+void FilePath::asyncWriteFileContents(const Continuation<const expected_str<qint64> &> &cont,
-        const Continuation<bool> &cont,
                                       const QByteArray &data,
                                       qint64 offset) const
 {
@@ -1315,33 +1315,47 @@ bool FilePath::removeRecursively(QString *error) const
     return fileAccess()->removeRecursively(*this, error);
 }
 
-bool FilePath::copyFile(const FilePath &target) const
+expected_str<void> FilePath::copyFile(const FilePath &target) const
 {
     if (host() != target.host()) {
         // FIXME: This does not scale.
-        const std::optional<QByteArray> ba = fileContents();
+        const expected_str<QByteArray> contents = fileContents();
-        if (!ba)
+        if (!contents) {
-            return false;
+            return make_unexpected(
-        const auto perms = permissions();
+                Tr::tr("Error while trying to copy file: %1").arg(contents.error()));
-        if (!target.writeFileContents(*ba))
+        }
-            return false;
+
+        const QFile::Permissions perms = permissions();
+        const expected_str<qint64> copyResult = target.writeFileContents(*contents);
+
+        if (!copyResult)
+            return make_unexpected(Tr::tr("Could not copy file: %1").arg(copyResult.error()));
 
         if (!target.setPermissions(perms)) {
             target.removeFile();
-            return false;
+            return make_unexpected(
+                Tr::tr("Could not set permissions on \"%1\"").arg(target.toString()));
         }
 
-        return true;
+        return {};
     }
     return fileAccess()->copyFile(*this, target);
 }
 
-void FilePath::asyncCopyFile(const std::function<void(bool)> &cont, const FilePath &target) const
+void FilePath::asyncCopyFile(const Continuation<const expected_str<void> &> &cont,
+                             const FilePath &target) const
 {
     if (host() != target.host()) {
-        asyncFileContents([cont, target](const std::optional<QByteArray> &ba) {
+        asyncFileContents([cont, target](const expected_str<QByteArray> &contents) {
-            if (ba)
+            if (contents)
-                target.asyncWriteFileContents(cont, *ba);
+                target.asyncWriteFileContents(
+                    [cont](const expected_str<qint64> &result) {
+                        if (result)
+                            cont({});
+                        else
+                            cont(make_unexpected(result.error()));
+                    },
+                    *contents);
         });
         return;
     }

src/libs/utils/filepath.h

@@ -5,6 +5,7 @@
 
 #include "utils_global.h"
 
+#include "expected.h"
 #include "filepathinfo.h"
 #include "osspecificaspects.h"
 
@@ -119,15 +120,15 @@ public:
     OsType osType() const;
     bool removeFile() const;
     bool removeRecursively(QString *error = nullptr) const;
-    bool copyFile(const FilePath &target) const;
+    expected_str<void> copyFile(const FilePath &target) const;
     bool renameFile(const FilePath &target) const;
     qint64 fileSize() const;
     qint64 bytesAvailable() const;
     bool createDir() const;
     FilePaths dirEntries(const FileFilter &filter, QDir::SortFlags sort = QDir::NoSort) const;
     FilePaths dirEntries(QDir::Filters filters) const;
-    std::optional<QByteArray> fileContents(qint64 maxSize = -1, qint64 offset = 0) const;
+    expected_str<QByteArray> fileContents(qint64 maxSize = -1, qint64 offset = 0) const;
-    bool writeFileContents(const QByteArray &data, qint64 offset = 0) const;
+    expected_str<qint64> writeFileContents(const QByteArray &data, qint64 offset = 0) const;
     FilePathInfo filePathInfo() const;
 
     bool operator==(const FilePath &other) const;
@@ -198,11 +199,12 @@ public:
     static void sort(FilePaths &files);
 
     // Asynchronous interface
-    void asyncCopyFile(const Continuation<bool> &cont, const FilePath &target) const;
+    void asyncCopyFile(const Continuation<const expected_str<void> &> &cont,
-    void asyncFileContents(const Continuation<const std::optional<QByteArray> &> &cont,
+                       const FilePath &target) const;
+    void asyncFileContents(const Continuation<const expected_str<QByteArray> &> &cont,
                            qint64 maxSize = -1,
                            qint64 offset = 0) const;
-    void asyncWriteFileContents(const Continuation<bool> &cont,
+    void asyncWriteFileContents(const Continuation<const expected_str<qint64> &> &cont,
                                 const QByteArray &data,
                                 qint64 offset = 0) const;
 

src/libs/utils/filesearch.cpp

@@ -55,7 +55,7 @@ static bool getFileContent(const FilePath &filePath,
     if (fileToContentsMap.contains(filePath)) {
         *tempString = fileToContentsMap.value(filePath);
     } else {
-        const std::optional<QByteArray> content = filePath.fileContents();
+        const expected_str<QByteArray> content = filePath.fileContents();
         if (!content)
             return false;
         *tempString = QTC_GUARD(encoding) ? encoding->toUnicode(*content)

src/libs/utils/fileutils.cpp

@@ -55,29 +55,13 @@ bool FileReader::fetch(const FilePath &filePath, QIODevice::OpenMode mode)
 {
     QTC_ASSERT(!(mode & ~(QIODevice::ReadOnly | QIODevice::Text)), return false);
 
-    if (filePath.needsDevice()) {
+    const expected_str<QByteArray> contents = filePath.fileContents();
-        const std::optional<QByteArray> contents = filePath.fileContents();
     if (!contents) {
-            m_errorString = tr("Cannot read %1").arg(filePath.toUserOutput());
+        m_errorString = contents.error();
         return false;
     }
     m_data = *contents;
     return true;
-    }
-
-    QFile file(filePath.toString());
-    if (!file.open(QIODevice::ReadOnly | mode)) {
-        m_errorString = tr("Cannot open %1 for reading: %2").arg(
-                filePath.toUserOutput(), file.errorString());
-        return false;
-    }
-    m_data = file.readAll();
-    if (file.error() != QFile::NoError) {
-        m_errorString = tr("Cannot read %1: %2").arg(
-                filePath.toUserOutput(), file.errorString());
-        return false;
-    }
-    return true;
 }
 
 bool FileReader::fetch(const FilePath &filePath, QIODevice::OpenMode mode, QString *errorString)
@@ -225,10 +209,10 @@ bool FileSaver::finalize()
         m_file->close();
         m_file->open(QIODevice::ReadOnly);
         const QByteArray data = m_file->readAll();
-        const bool res = m_filePath.writeFileContents(data);
+        const expected_str<qint64> res = m_filePath.writeFileContents(data);
         m_file->remove();
         m_file.reset();
-        return res;
+        return res.has_value();
     }
 
     if (!m_isSafe)
@@ -703,15 +687,20 @@ bool FileUtils::copyIfDifferent(const FilePath &srcFilePath, const FilePath &tgt
         const QDateTime srcModified = srcFilePath.lastModified();
         const QDateTime tgtModified = tgtFilePath.lastModified();
         if (srcModified == tgtModified) {
-            const std::optional<QByteArray> srcContents = srcFilePath.fileContents();
+            // TODO: Create FilePath::hashFromContents() and compare hashes.
-            const std::optional<QByteArray> tgtContents = srcFilePath.fileContents();
+            const expected_str<QByteArray> srcContents = srcFilePath.fileContents();
-            if (srcContents == tgtContents)
+            const expected_str<QByteArray> tgtContents = srcFilePath.fileContents();
+            if (srcContents && srcContents == tgtContents)
                 return true;
         }
         tgtFilePath.removeFile();
     }
 
-    return srcFilePath.copyFile(tgtFilePath);
+    const expected_str<void> copyResult = srcFilePath.copyFile(tgtFilePath);
+
+    // TODO forward error to caller instead of assert, since IO errors can always be expected
+    QTC_ASSERT_EXPECTED(copyResult, return false);
+    return true;
 }
 
 QString FileUtils::fileSystemFriendlyName(const QString &name)

src/libs/utils/fsengine/fsengine_impl.cpp

@@ -4,6 +4,7 @@
 #include "fsengine_impl.h"
 
 #include "diriterator.h"
+#include "expected.h"
 #include "filepathinfocache.h"
 
 #include "../filepath.h"
@@ -62,8 +63,11 @@ bool FSEngineImpl::open(QIODevice::OpenMode openMode)
         return false;
 
     if (read || append) {
-        const std::optional<QByteArray> contents = m_filePath.fileContents();
+        const expected_str<QByteArray> readResult = m_filePath.fileContents();
-        QTC_ASSERT(contents && m_tempStorage->write(*contents) >= 0, return false);
+        QTC_ASSERT_EXPECTED(readResult, return false);
+
+        const expected_str<qint64> writeResult = m_tempStorage->write(*readResult);
+        QTC_ASSERT_EXPECTED(writeResult, return false);
 
         if (!append)
             m_tempStorage->seek(0);
@@ -133,7 +137,9 @@ bool FSEngineImpl::remove()
 
 bool FSEngineImpl::copy(const QString &newName)
 {
-    return m_filePath.copyFile(FilePath::fromString(newName));
+    expected_str<void> result = m_filePath.copyFile(FilePath::fromString(newName));
+    QTC_ASSERT_EXPECTED(result, return false);
+    return true;
 }
 
 bool FSEngineImpl::rename(const QString &newName)

src/plugins/android/androidbuildapkstep.cpp

@@ -680,7 +680,9 @@ static bool copyFileIfNewer(const FilePath &sourceFilePath,
 
     if (!destinationFilePath.parentDir().ensureWritableDir())
         return false;
-    return sourceFilePath.copyFile(destinationFilePath);
+    expected_str<void> result = sourceFilePath.copyFile(destinationFilePath);
+    QTC_ASSERT_EXPECTED(result, return false);
+    return true;
 }
 
 void AndroidBuildApkStep::doRun()

src/plugins/cmakeprojectmanager/fileapiparser.cpp

@@ -75,7 +75,7 @@ static QJsonDocument readJsonFile(const FilePath &filePath)
     qCDebug(cmakeFileApi) << "readJsonFile:" << filePath;
     QTC_ASSERT(!filePath.isEmpty(), return {});
 
-    const std::optional<QByteArray> contents = filePath.fileContents();
+    const expected_str<QByteArray> contents = filePath.fileContents();
     if (!contents)
         return {};
     const QJsonDocument doc = QJsonDocument::fromJson(*contents);

src/plugins/cmakeprojectmanager/presetsparser.cpp

@@ -2,10 +2,11 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0+ OR GPL-3.0 WITH Qt-GPL-exception-1.0
 
 #include "presetsparser.h"
-#include "utils/algorithm.h"
 
 #include "cmakeprojectmanagertr.h"
 
+#include <utils/algorithm.h>
+
 #include <QJsonArray>
 #include <QJsonDocument>
 #include <QJsonObject>
@@ -391,7 +392,7 @@ const PresetsData &PresetsParser::presetsData() const
 
 bool PresetsParser::parse(const Utils::FilePath &jsonFile, QString &errorMessage, int &errorLine)
 {
-    const std::optional<QByteArray> jsonContents = jsonFile.fileContents();
+    const Utils::expected_str<QByteArray> jsonContents = jsonFile.fileContents();
     if (!jsonContents) {
         errorMessage = Tr::tr("Failed to read %1 file").arg(jsonFile.fileName());
         return false;

src/plugins/coreplugin/loggingviewer.cpp

@@ -652,7 +652,7 @@ void LoggingViewManagerWidget::loadAndUpdateFromPreset()
     if (fp.isEmpty())
         return;
     // read file, update categories
-    const std::optional<QByteArray> contents = fp.fileContents();
+    const Utils::expected_str<QByteArray> contents = fp.fileContents();
     if (!contents) {
         QMessageBox::critical(ICore::dialogParent(),
                               tr("Error"),

src/plugins/cppeditor/cpptoolsjsextension.cpp

@@ -136,9 +136,8 @@ bool CppToolsJsExtension::hasQObjectParent(const QString &klassName) const
     const WorkingCopy workingCopy = CppModelManager::instance()->workingCopy();
     QByteArray source = workingCopy.source(item->filePath());
     if (source.isEmpty()) {
-        std::optional<QByteArray> contents = item->filePath().fileContents();
+        const Utils::expected_str<QByteArray> contents = item->filePath().fileContents();
-        if (!contents)
+        QTC_ASSERT_EXPECTED(contents, return false);
-            return false;
         source = *contents;
     }
     const auto doc = snapshot.preprocessedDocument(source, item->filePath());

src/plugins/debugger/debuggerprotocol.cpp

@@ -15,12 +15,7 @@
 #include <ctype.h>
 
 #include <utils/processhandle.h>
-
+#include <utils/qtcassert.h>
-#define QTC_ASSERT_STRINGIFY_HELPER(x) #x
-#define QTC_ASSERT_STRINGIFY(x) QTC_ASSERT_STRINGIFY_HELPER(x)
-#define QTC_ASSERT_STRING(cond) qDebug("SOFT ASSERT: \"" cond"\" in file " __FILE__ ", line " QTC_ASSERT_STRINGIFY(__LINE__))
-#define QTC_ASSERT(cond, action) if (cond) {} else { QTC_ASSERT_STRING(#cond); action; } do {} while (0)
-#define QTC_CHECK(cond) if (cond) {} else { QTC_ASSERT_STRING(#cond); } do {} while (0)
 
 namespace Debugger::Internal {
 

src/plugins/gitlab/gitlabparameters.cpp

@@ -129,7 +129,7 @@ static QList<GitLabServer> readTokensFile(const Utils::FilePath &filePath)
 {
     if (!filePath.exists())
         return {};
-    std::optional<QByteArray> contents = filePath.fileContents();
+    const Utils::expected_str<QByteArray> contents = filePath.fileContents();
     if (!contents)
         return {};
     const QByteArray content = *contents;

src/plugins/projectexplorer/extracompiler.cpp

@@ -16,6 +16,7 @@
 #include <texteditor/texteditorconstants.h>
 #include <texteditor/fontsettings.h>
 
+#include <utils/expected.h>
 #include <utils/qtcassert.h>
 #include <utils/qtcprocess.h>
 #include <utils/runextensions.h>
@@ -98,7 +99,9 @@ ExtraCompiler::ExtraCompiler(const Project *project, const FilePath &source,
         if (!d->compileTime.isValid() || d->compileTime > lastModified)
             d->compileTime = lastModified;
 
-        if (const std::optional<QByteArray> contents = target.fileContents())
+        const expected_str<QByteArray> contents = target.fileContents();
+        QTC_ASSERT_EXPECTED(contents, return);
+
         setContent(target, *contents);
     }
 }
@@ -169,11 +172,12 @@ void ExtraCompiler::onTargetsBuilt(Project *project)
             if (d->compileTime >= generateTime)
                 return;
 
-            if (const std::optional<QByteArray> contents = target.fileContents()) {
+            const expected_str<QByteArray> contents = target.fileContents();
+            QTC_ASSERT_EXPECTED(contents, return);
+
             d->compileTime = generateTime;
             setContent(target, *contents);
         }
-        }
     });
 }
 

src/plugins/qmldesigner/components/contentlibrary/contentlibrarybundleimporter.cpp

@@ -224,7 +224,7 @@ void ContentLibraryBundleImporter::handleImportTimer()
 QVariantHash ContentLibraryBundleImporter::loadAssetRefMap(const Utils::FilePath &bundlePath)
 {
     FilePath assetRefPath = bundlePath.resolvePath(QLatin1String(Constants::COMPONENT_BUNDLES_ASSET_REF_FILE));
-    const std::optional<QByteArray> content = assetRefPath.fileContents();
+    const Utils::expected_str<QByteArray> content = assetRefPath.fileContents();
     if (content) {
         QJsonParseError error;
         QJsonDocument bundleDataJsonDoc = QJsonDocument::fromJson(*content, &error);
@@ -266,7 +266,7 @@ QString ContentLibraryBundleImporter::unimportComponent(const QString &qmlFile)
     removedFiles.append(qmlFile);
 
     FilePath qmldirPath = bundleImportPath.resolvePath(QStringLiteral("qmldir"));
-    const std::optional<QByteArray> qmldirContent = qmldirPath.fileContents();
+    const expected_str<QByteArray> qmldirContent = qmldirPath.fileContents();
     QByteArray newContent;
 
     QString qmlType = qmlFilePath.baseName();

src/plugins/squish/scripthelper.cpp

@@ -144,7 +144,9 @@ bool ScriptHelper::writeScriptFile(const Utils::FilePath &outScriptFile,
     for (const QByteArray &line : functionFooter(m_language))
         data.append(line).append('\n');
 
-    return outScriptFile.writeFileContents(data);
+    const Utils::expected_str<qint64> result = outScriptFile.writeFileContents(data);
+    QTC_ASSERT_EXPECTED(result, return false);
+    return true;
 }
 
 } // namespace Internal

src/plugins/squish/squishtesttreeview.cpp

@@ -179,8 +179,8 @@ static bool copyScriptTemplates(const SuiteConf &suiteConf, const Utils::FilePat
     const Utils::FilePath test = scripts.pathAppended(testStr + extension);
     const Utils::FilePath testFile = destination.pathAppended("test" + extension);
     QTC_ASSERT(!testFile.exists(), return false);
-    ok = test.copyFile(testFile);
+    const Utils::expected_str<void> result = test.copyFile(testFile);
-    QTC_ASSERT(ok, return false);
+    QTC_ASSERT_EXPECTED(result, return false)
 
     if (scripted)
         ok = suiteConf.ensureObjectMapExists();

src/plugins/squish/suiteconf.cpp

@@ -80,7 +80,7 @@ static QMap<QString, QString> readSuiteConfContent(const Utils::FilePath &file)
     if (!file.isReadableFile())
         return {};
 
-    std::optional<QByteArray> suiteConfContent = file.fileContents();
+    const Utils::expected_str<QByteArray> suiteConfContent = file.fileContents();
     if (!suiteConfContent)
         return {};
 
@@ -112,7 +112,9 @@ static bool writeSuiteConfContent(const Utils::FilePath &file, const QMap<QStrin
         else
             outData.append(it.key().toUtf8()).append('=').append(it.value().toUtf8()).append('\n');
     }
-    return file.writeFileContents(outData);
+    const Utils::expected_str<qint64> result = file.writeFileContents(outData);
+    QTC_ASSERT_EXPECTED(result, return false);
+    return true;
 }
 
 bool SuiteConf::read()
@@ -306,9 +308,9 @@ bool SuiteConf::ensureObjectMapExists() const
     const Utils::FilePath objectMap = scripts.pathAppended("objectmap_template" + extension);
     bool ok = destinationObjectMap.parentDir().ensureWritableDir();
     QTC_ASSERT(ok, return false);
-    ok = objectMap.copyFile(destinationObjectMap);
+    const Utils::expected_str<void> result = objectMap.copyFile(destinationObjectMap);
-    QTC_ASSERT(ok, return false);
+    QTC_ASSERT_EXPECTED(result, return false);
-    return ok;
+    return true;
 }
 
 } // namespace Internal

src/plugins/valgrind/callgrindengine.cpp

@@ -256,9 +256,8 @@ void CallgrindToolRunner::triggerParse()
         m_hostOutputFile = FilePath::fromString(dataFile.fileName());
     }
 
-    const auto afterCopy = [this](bool res) {
+    const auto afterCopy = [this](expected_str<void> res) {
-        QTC_CHECK(res);
+        QTC_ASSERT_EXPECTED(res, return);
-        QTC_ASSERT(m_hostOutputFile.exists(), return);
         showStatusMessage(Tr::tr("Parsing Profile Data..."));
         m_parser.parse(m_hostOutputFile);
     };

tests/auto/utils/CMakeLists.txt

@@ -2,6 +2,7 @@ add_subdirectory(ansiescapecodehandler)
 add_subdirectory(asynctask)
 add_subdirectory(commandline)
 add_subdirectory(deviceshell)
+add_subdirectory(expected)
 add_subdirectory(fileutils)
 add_subdirectory(fsengine)
 add_subdirectory(fuzzymatcher)

tests/auto/utils/expected/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_qtc_test(tst_utils_expected
+  DEPENDS Utils
+  SOURCES tst_expected.cpp
+)

tests/auto/utils/expected/expected.qbs

@@ -0,0 +1,7 @@
+import qbs
+
+QtcAutotest {
+    name: "Expected autotest"
+    Depends { name: "Utils" }
+    files: "tst_expected.cpp"
+}

tests/auto/utils/expected/tst_expected.cpp

@@ -0,0 +1,38 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0+ OR GPL-3.0 WITH Qt-GPL-exception-1.0
+
+#include <QtTest/qtestcase.h>
+#include <QtTest>
+
+#include <utils/expected.h>
+#include <utils/filepath.h>
+
+using namespace Utils;
+
+class tst_expected : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void initTestCase() {}
+
+    void tryMonads()
+    {
+        FilePath p = "idontexists.ne";
+
+        auto result = p.fileContents()
+                          .and_then([](auto) { return expected_str<QByteArray>{}; })
+                          .or_else([](auto error) {
+                              return expected_str<QByteArray>(
+                                  make_unexpected(QString("Error: " + error)));
+                          })
+                          .transform_or([](auto error) -> QString {
+                              return QString(QString("More Info: ") + error);
+                          });
+
+        QVERIFY(!result);
+    }
+};
+QTEST_GUILESS_MAIN(tst_expected)
+
+#include "tst_expected.moc"

tests/auto/utils/fileutils/tst_fileutils.cpp

@@ -1,9 +1,9 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0+ OR GPL-3.0 WITH Qt-GPL-exception-1.0
 
-#include <QtTest>
 #include <QDebug>
 #include <QRandomGenerator>
+#include <QtTest>
 
 #include <utils/fileutils.h>
 #include <utils/hostosinfo.h>
@@ -13,12 +13,12 @@
 using namespace Utils;
 
 namespace QTest {
-    template<>
+template<>
-    char *toString(const FilePath &filePath)
+char *toString(const FilePath &filePath)
-    {
+{
     return qstrdup(filePath.toString().toLocal8Bit().constData());
-    }
 }
+} // namespace QTest
 
 class tst_fileutils : public QObject
 {
@@ -1027,7 +1027,7 @@ void tst_fileutils::asyncLocalCopy()
     const FilePath orig = FilePath::fromString(rootPath).pathAppended("x/y/fileToCopy.txt");
     QVERIFY(orig.exists());
     const FilePath dest = FilePath::fromString(rootPath).pathAppended("x/fileToCopyDest.txt");
-    auto afterCopy = [&orig, &dest, this] (bool result) {
+    auto afterCopy = [&orig, &dest, this](expected_str<void> result) {
         QVERIFY(result);
         // check existence, size and content
         QVERIFY(dest.exists());

tests/auto/utils/utils.qbs

@@ -7,6 +7,7 @@ Project {
         "asynctask/asynctask.qbs",
         "commandline/commandline.qbs",
         "deviceshell/deviceshell.qbs",
+        "expected/expected.qbs",
         "fileutils/fileutils.qbs",
         "fsengine/fsengine.qbs",
         "fuzzymatcher/fuzzymatcher.qbs",