Revert "Clang: Stop enabling exceptions explicitly"

This reverts commit b114f77d8a as
"--driver-mode=cl" apparently still disables exceptions.

Task-number: QTCREATORBUG-23000
Change-Id: I9c49d971fafda5e1aca8445f8921e50f323d368f
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/cpptools/compileroptionsbuilder.cpp

@@ -136,6 +136,7 @@ QStringList CompilerOptionsBuilder::build(ProjectFile::Kind fileKind,
     addTargetTriple();
     updateFileLanguage(fileKind);
     addLanguageVersionAndExtensions();
+    enableExceptions();
 
     addPrecompiledHeaderOptions(usePrecompiledHeaders);
     addProjectConfigFileInclude();
@@ -270,6 +271,17 @@ void CompilerOptionsBuilder::addCompilerFlags()
     add(m_compilerFlags.flags);
 }
 
+void CompilerOptionsBuilder::enableExceptions()
+{
+    // With "--driver-mode=cl" exceptions are disabled (clang 8).
+    // This is most likely due to incomplete exception support of clang.
+    // However, as we need exception support only in the frontend,
+    // enabling them explicitly should be fine.
+    if (m_projectPart.languageVersion > ::Utils::LanguageVersion::LatestC)
+        add("-fcxx-exceptions");
+    add("-fexceptions");
+}
+
 static QString creatorResourcePath()
 {
 #ifndef UNIT_TESTS

src/plugins/cpptools/compileroptionsbuilder.h

@@ -69,6 +69,7 @@ public:
     void addExtraCodeModelFlags();
     void addPicIfCompilerFlagsContainsIt();
     void addCompilerFlags();
+    void enableExceptions();
     void insertWrappedQtHeaders();
     void addLanguageVersionAndExtensions();
     void updateFileLanguage(ProjectFile::Kind fileKind);

tests/unit/unittest/compileroptionsbuilder-test.cpp

@@ -444,6 +444,22 @@ TEST_F(CompilerOptionsBuilder, AddTargetTriple)
     ASSERT_THAT(compilerOptionsBuilder.options(), ElementsAre("--target=x86_64-apple-darwin10"));
 }
 
+TEST_F(CompilerOptionsBuilder, EnableCExceptions)
+{
+    projectPart.languageVersion = Utils::LanguageVersion::C99;
+
+    compilerOptionsBuilder.enableExceptions();
+
+    ASSERT_THAT(compilerOptionsBuilder.options(), ElementsAre("-fexceptions"));
+}
+
+TEST_F(CompilerOptionsBuilder, EnableCXXExceptions)
+{
+    compilerOptionsBuilder.enableExceptions();
+
+    ASSERT_THAT(compilerOptionsBuilder.options(), ElementsAre("-fcxx-exceptions", "-fexceptions"));
+}
+
 TEST_F(CompilerOptionsBuilder, InsertWrappedQtHeaders)
 {
     CppTools::CompilerOptionsBuilder compilerOptionsBuilder{projectPart,
@@ -601,6 +617,8 @@ TEST_F(CompilerOptionsBuilder, BuildAllOptions)
                             "-x",
                             "c++",
                             "-std=c++17",
+                            "-fcxx-exceptions",
+                            "-fexceptions",
                             "-DprojectFoo=projectBar",
                             "-I", IsPartOfHeader("wrappedQtHeaders"),
                             "-I", IsPartOfHeader(toNative("wrappedQtHeaders/QtCore").toStdString()),
@@ -632,6 +650,8 @@ TEST_F(CompilerOptionsBuilder, BuildAllOptionsCl)
                             "--target=x86_64-apple-darwin10",
                             "/TP",
                             "/std:c++17",
+                            "-fcxx-exceptions",
+                            "-fexceptions",
                             "-fms-compatibility-version=19.00",
                             "-DprojectFoo=projectBar",
                             "-D__FUNCSIG__=\"\"",