Clang: Avoid consuming gcc internal include paths

Given the (default) include paths of GCC, e.g.

 /usr/include/c++/7
 /usr/include/x86_64-linux-gnu/c++/7
 /usr/include/c++/7/backward
 /usr/lib/gcc/x86_64-linux-gnu/7/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/7/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include

discard gcc-internal paths like /usr/lib/gcc/x86_64-linux-gnu/7/include
as they are not relevant for clang and even confuse it with regard to
 #include_next.

Paths below the gcc install dir are considered as gcc-internal. The
install dir is queried with

  $ gcc -print-search-dirs

Some GCC distributions, like MinGW, ship the standard library headers in
the install dir. Ensure to not discard these.

Fixes: QTCREATORBUG-22898
Change-Id: Ia85258fb01b72ad073e71390e003fe8268e3b01f
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

1 files changed, 46 insertions, 0 deletions

diff --git a/tests/unit/unittest/headerpathfilter-test.cpp b/tests/unit/unittest/headerpathfilter-test.cpp
index 79091e0a0b..dac2974ecf 100644
--- a/tests/unit/unittest/headerpathfilter-test.cpp
+++ b/tests/unit/unittest/headerpathfilter-test.cpp
@@ -27,6 +27,7 @@
 
 #include <cpptools/headerpathfilter.h>
 #include <projectexplorer/project.h>
+#include <projectexplorer/projectexplorerconstants.h>
 
 namespace {
 
@@ -248,6 +249,51 @@ TEST_F(HeaderPathFilter, ClangHeadersAndCppIncludesPathsOrderLinux)
                             HasBuiltIn("/builtin_path")));
 }
 
+// Include paths below the installation dir should be removed as they confuse clang.
+TEST_F(HeaderPathFilter, RemoveGccInternalPaths)
+{
+    projectPart.toolChainInstallDir = Utils::FilePath::fromUtf8("/usr/lib/gcc/x86_64-linux-gnu/7");
+    projectPart.toolchainType = ProjectExplorer::Constants::GCC_TOOLCHAIN_TYPEID;
+    projectPart.headerPaths = {
+        HeaderPath{"/usr/lib/gcc/x86_64-linux-gnu/7/include", HeaderPathType::BuiltIn},
+        HeaderPath{"/usr/lib/gcc/x86_64-linux-gnu/7/include-fixed", HeaderPathType::BuiltIn},
+    };
+    CppTools::HeaderPathFilter filter{projectPart,
+                                      CppTools::UseTweakedHeaderPaths::Yes,
+                                      "6.0",
+                                      CLANG_RESOURCE_DIR};
+
+    filter.process();
+
+    ASSERT_THAT(filter.builtInHeaderPaths, ElementsAre(HasBuiltIn(CLANG_RESOURCE_DIR)));
+}
+
+// MinGW ships the standard library headers in "<installdir>/include/c++".
+// Ensure that we do not remove include paths pointing there.
+TEST_F(HeaderPathFilter, RemoveGccInternalPathsExceptForStandardPaths)
+{
+    projectPart.toolChainInstallDir = Utils::FilePath::fromUtf8(
+        "c:/mingw730_64/lib/gcc/x86_64-w64-mingw32/7.3.0");
+    projectPart.toolchainType = ProjectExplorer::Constants::MINGW_TOOLCHAIN_TYPEID;
+    projectPart.headerPaths = {
+        HeaderPath{"c:/mingw730_64/lib/gcc/x86_64-w64-mingw32/7.3.0/include/c++", HeaderPathType::BuiltIn},
+        HeaderPath{"c:/mingw730_64/lib/gcc/x86_64-w64-mingw32/7.3.0/include/c++/x86_64-w64-mingw32", HeaderPathType::BuiltIn},
+        HeaderPath{"c:/mingw730_64/lib/gcc/x86_64-w64-mingw32/7.3.0/include/c++/backward", HeaderPathType::BuiltIn},
+    };
+
+    auto expected = projectPart.headerPaths;
+    expected << HeaderPath{CLANG_RESOURCE_DIR, HeaderPathType::BuiltIn};
+
+    CppTools::HeaderPathFilter filter{projectPart,
+                                      CppTools::UseTweakedHeaderPaths::Yes,
+                                      "6.0",
+                                      CLANG_RESOURCE_DIR};
+
+    filter.process();
+
+    ASSERT_THAT(filter.builtInHeaderPaths, ContainerEq(expected));
+}
+
 TEST_F(HeaderPathFilter, ClangHeadersAndCppIncludesPathsOrderNoVersion)
 {
     projectPart.headerPaths = {