ProjectExplorer: Improve error reporting

Previously anytime a FilePath operation tried to access a device that
does not have a DeviceFileAccess an error message would be thrown.

This patch makes it possible to differentiate between the device not
being found, and the device just not having a DeviceFileAccess
interface.

Also the error message in DeviceFileAccess::exists() was removed as
its not an error to ask if something exists even if it does not.

Change-Id: Ib8c2e08132159d0d97bcd049b59436eb17bdbacd
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/devicefileaccess.cpp

@@ -120,7 +120,6 @@ bool DeviceFileAccess::createDirectory(const FilePath &filePath) const
 bool DeviceFileAccess::exists(const FilePath &filePath) const
 {
     Q_UNUSED(filePath)
-    QTC_CHECK(false);
     return false;
 }
 

src/libs/utils/filepath.cpp

@@ -939,9 +939,9 @@ DeviceFileAccess *FilePath::fileAccess() const
     }
 
     static DeviceFileAccess dummy;
-    DeviceFileAccess *access = s_deviceHooks.fileAccess(*this);
-    QTC_ASSERT(access, qDebug() << toString(); return &dummy);
-    return access;
+    const expected_str<DeviceFileAccess *> access = s_deviceHooks.fileAccess(*this);
+    QTC_ASSERT_EXPECTED(access, return &dummy);
+    return *access ? *access : &dummy;
 }
 
 /*!

src/libs/utils/filepath.h

@@ -269,7 +269,7 @@ class QTCREATOR_UTILS_EXPORT DeviceFileHooks
 public:
     static DeviceFileHooks &instance();
 
-    std::function<DeviceFileAccess *(const FilePath &)> fileAccess;
+    std::function<expected_str<DeviceFileAccess *>(const FilePath &)> fileAccess;
     std::function<QString(const FilePath &)> deviceDisplayName;
     std::function<bool(const FilePath &, const FilePath &)> ensureReachable;
     std::function<Environment(const FilePath &)> environment;

src/plugins/projectexplorer/devicesupport/devicemanager.cpp

@@ -422,11 +422,14 @@ DeviceManager::DeviceManager(bool isInstance) : d(std::make_unique<DeviceManager
         return device->localSource(file);
     };
 
-    deviceHooks.fileAccess = [](const FilePath &filePath) -> DeviceFileAccess * {
+    deviceHooks.fileAccess = [](const FilePath &filePath) -> expected_str<DeviceFileAccess *> {
         if (!filePath.needsDevice())
             return DesktopDeviceFileAccess::instance();
         auto device = DeviceManager::deviceForPath(filePath);
-        QTC_ASSERT(device, qDebug() << filePath.toString(); return nullptr);
+        if (!device) {
+            return make_unexpected(
+                QString("No device found for path \"%1\"").arg(filePath.toUserOutput()));
+        }
         return device->fileAccess();
     };