CppTools: Allow interpreting ambiguous headers as C headers

...instead of C++ headers.

For the Clang Code Model this results in using "-x c-header" instead of
"-x c++-header".

This introduces a new option in Options > C++ > "Code Model" to
configure this.

Change-Id: I8a0ce8fa6155f5ef58743ebc7f1d0b500fbf6599
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/plugins/cpptools/cppcodemodelsettings.cpp

@@ -58,6 +58,9 @@ static QString clangDiagnosticConfigsArrayOptionsKey()
 static QString pchUsageKey()
 { return QLatin1String(Constants::CPPTOOLS_MODEL_MANAGER_PCH_USAGE); }
 
+static QString interpretAmbiguousHeadersAsCHeadersKey()
+{ return QLatin1String(Constants::CPPTOOLS_INTERPRET_AMBIGIUOUS_HEADERS_AS_C_HEADERS); }
+
 static QString skipIndexingBigFilesKey()
 { return QLatin1String(Constants::CPPTOOLS_SKIP_INDEXING_BIG_FILES); }
 
@@ -88,6 +91,10 @@ void CppCodeModelSettings::fromSettings(QSettings *s)
     const QVariant pchUsageVariant = s->value(pchUsageKey(), initialPchUsage());
     setPCHUsage(static_cast<PCHUsage>(pchUsageVariant.toInt()));
 
+    const QVariant interpretAmbiguousHeadersAsCHeaders
+            = s->value(interpretAmbiguousHeadersAsCHeadersKey(), false);
+    setInterpretAmbigiousHeadersAsCHeaders(interpretAmbiguousHeadersAsCHeaders.toBool());
+
     const QVariant skipIndexingBigFiles = s->value(skipIndexingBigFilesKey(), true);
     setSkipIndexingBigFiles(skipIndexingBigFiles.toBool());
 
@@ -116,6 +123,8 @@ void CppCodeModelSettings::toSettings(QSettings *s)
 
     s->setValue(clangDiagnosticConfigKey(), clangDiagnosticConfigId().toSetting());
     s->setValue(pchUsageKey(), pchUsage());
+
+    s->setValue(interpretAmbiguousHeadersAsCHeadersKey(), interpretAmbigiousHeadersAsCHeaders());
     s->setValue(skipIndexingBigFilesKey(), skipIndexingBigFiles());
     s->setValue(indexerFileSizeLimitKey(), indexerFileSizeLimitInMb());
 
@@ -166,6 +175,16 @@ void CppCodeModelSettings::emitChanged()
     emit changed();
 }
 
+bool CppCodeModelSettings::interpretAmbigiousHeadersAsCHeaders() const
+{
+    return m_interpretAmbigiousHeadersAsCHeaders;
+}
+
+void CppCodeModelSettings::setInterpretAmbigiousHeadersAsCHeaders(bool yesno)
+{
+    m_interpretAmbigiousHeadersAsCHeaders = yesno;
+}
+
 bool CppCodeModelSettings::skipIndexingBigFiles() const
 {
     return m_skipIndexingBigFiles;