Support 'CONFIG += precompile_header_c' in VS projects

The CONFIG value precompile_header_c was ignored in the VS project
generator. Add a member VcprojGenerator::pchIsCFile that is set to
true if precompile_header_c is active.
The code in modifyPCHstage had to be rearranged to separate the three
parts for stable.h, stable.cpp and other files.

Task-number: QTBUG-62821
Change-Id: I340eb165baa22cafcb64815cf223ce9a21aca558
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

qmake/generators/win32/msvc_objectmodel.cpp

@@ -2213,20 +2213,8 @@ void VCFilter::addFiles(const ProStringList& fileList)
 
 void VCFilter::modifyPCHstage(QString str)
 {
-    bool pchThroughSourceFile = !Project->precompSource.isEmpty();
-    bool isCFile = false;
-    for (QStringList::Iterator it = Option::c_ext.begin(); it != Option::c_ext.end(); ++it) {
-        if (str.endsWith(*it)) {
-            isCFile = true;
-            break;
-        }
-    }
     const bool isHFile = (str == Project->precompH);
-    bool isCPPFile = pchThroughSourceFile && (str == Project->precompSource);
+    const bool pchThroughSourceFile = !Project->precompSource.isEmpty();
-
-    if(!isCFile && !isHFile && !isCPPFile)
-        return;
-
     if (isHFile && pchThroughSourceFile && Project->autogenPrecompSource) {
         useCustomBuildTool = true;
         QString toFile(Project->precompSource);
@@ -2259,13 +2247,29 @@ void VCFilter::modifyPCHstage(QString str)
     }
 
     useCompilerTool = true;
-    // Setup PCH options
+    const bool isPrecompSource = pchThroughSourceFile && (str == Project->precompSource);
-    CompilerTool.UsePrecompiledHeader     = (isCFile ? pchNone : pchCreateUsingSpecific);
+    if (isPrecompSource) {
-    if (isCFile)
+        CompilerTool.UsePrecompiledHeader = pchCreateUsingSpecific;
-        CompilerTool.PrecompiledHeaderThrough = QLatin1String("$(NOINHERIT)");
+        if (Project->autogenPrecompSource)
-    else if (Project->autogenPrecompSource)
             CompilerTool.PrecompiledHeaderThrough = Project->precompHFilename;
         CompilerTool.ForcedIncludeFiles = QStringList("$(NOINHERIT)");
+        return;
+    }
+
+    bool isCFile = false;
+    for (QStringList::Iterator it = Option::c_ext.begin(); it != Option::c_ext.end(); ++it) {
+        if (str.endsWith(*it)) {
+            isCFile = true;
+            break;
+        }
+    }
+
+    bool pchCompatible = (isCFile == Project->pchIsCFile);
+    if (!pchCompatible) {
+        CompilerTool.UsePrecompiledHeader = pchNone;
+        CompilerTool.PrecompiledHeaderThrough = QLatin1String("$(NOINHERIT)");
+        CompilerTool.ForcedIncludeFiles = QStringList("$(NOINHERIT)");
+    }
 }
 
 VCFilterFile VCFilter::findFile(const QString &filePath, bool *found) const

qmake/generators/win32/msvc_vcproj.cpp

@@ -776,7 +776,8 @@ void VcprojGenerator::init()
     // Setup PCH variables
     precompH = project->first("PRECOMPILED_HEADER").toQString();
     precompSource = project->first("PRECOMPILED_SOURCE").toQString();
-    usePCH = !precompH.isEmpty() && project->isActiveConfig("precompile_header");
+    pchIsCFile = project->isActiveConfig("precompile_header_c");
+    usePCH = !precompH.isEmpty() && (pchIsCFile || project->isActiveConfig("precompile_header"));
     if (usePCH) {
         precompHFilename = fileInfo(precompH).fileName();
         // Created files
@@ -793,7 +794,9 @@ void VcprojGenerator::init()
         autogenPrecompSource = precompSource.isEmpty() && project->isActiveConfig("autogen_precompile_source");
         if (autogenPrecompSource) {
             precompSource = precompH
-                + (Option::cpp_ext.count() ? Option::cpp_ext.at(0) : QLatin1String(".cpp"));
+                    + (pchIsCFile
+                       ? (Option::c_ext.count() ? Option::c_ext.at(0) : QLatin1String(".c"))
+                       : (Option::cpp_ext.count() ? Option::cpp_ext.at(0) : QLatin1String(".cpp")));
             project->values("GENERATED_SOURCES") += precompSource;
         } else if (!precompSource.isEmpty()) {
             project->values("SOURCES") += precompSource;

qmake/generators/win32/msvc_vcproj.h

@@ -66,6 +66,7 @@ public:
     QHash<QString, QString> extraCompilerOutputs;
     const QString customBuildToolFilterFileSuffix;
     bool usePCH;
+    bool pchIsCFile = false;
     VCProjectWriter *projectWriter;
 
 protected: