Fix regression in -I/usr/include exclusion logic

The change in commit 15ad830062 (Refactor exclusion of -I/usr/include to
avoid per-language values, 2019-01-21, v3.14.0-rc1~108^2~4) caused the
exclusion to apply to Fortran, but it was only meant for C, CXX, and
CUDA.  The purpose of the change was to prepare for the value of
`CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES` to be computed from the
actual compiler instead of hard-coded.  We need to preserve exclusion of
`-I/usr/include` if the compiler has any implicit include directory that
looks intended to replace it, e.g. `<sdk>/usr/include` on macOS.

Fixes: #18914

2 files changed, 16 insertions, 11 deletions

diff --git a/Modules/Platform/UnixPaths.cmake b/Modules/Platform/UnixPaths.cmake
index 4ae4514..46c24bb 100644
--- a/Modules/Platform/UnixPaths.cmake
+++ b/Modules/Platform/UnixPaths.cmake
@@ -63,11 +63,6 @@ list(APPEND CMAKE_PLATFORM_IMPLICIT_LINK_DIRECTORIES
   /lib /lib32 /lib64 /usr/lib /usr/lib32 /usr/lib64
   )
 
-# Platform-wide directories to avoid adding via -I<dir>.
-list(APPEND CMAKE_PLATFORM_IMPLICIT_INCLUDE_DIRECTORIES
-  /usr/include
-  )
-
 # Default per-language values.  These may be later replaced after
 # parsing the implicit directory information from compiler output.
 set(_CMAKE_C_IMPLICIT_INCLUDE_DIRECTORIES_INIT
diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index 252aa4c..b1115ea 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -939,12 +939,6 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
     // Raw list of implicit include directories
     std::vector<std::string> impDirVec;
 
-    // Get platform-wide implicit directories.
-    if (const char* implicitIncludes = (this->Makefile->GetDefinition(
-          "CMAKE_PLATFORM_IMPLICIT_INCLUDE_DIRECTORIES"))) {
-      cmSystemTools::ExpandListArgument(implicitIncludes, impDirVec);
-    }
-
     // Load implicit include directories for this language.
     std::string key = "CMAKE_";
     key += lang;
@@ -953,6 +947,22 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
       cmSystemTools::ExpandListArgument(value, impDirVec);
     }
 
+    // The Platform/UnixPaths module used to hard-code /usr/include for C, CXX,
+    // and CUDA in CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES, but those
+    // variables are now computed.  On macOS the /usr/include directory is
+    // inside the platform SDK so the computed value does not contain it
+    // directly.  In this case adding -I/usr/include can hide SDK headers so we
+    // must still exclude it.
+    if ((lang == "C" || lang == "CXX" || lang == "CUDA") &&
+        std::find(impDirVec.begin(), impDirVec.end(), "/usr/include") ==
+          impDirVec.end() &&
+        std::find_if(impDirVec.begin(), impDirVec.end(),
+                     [](std::string const& d) {
+                       return cmHasLiteralSuffix(d, "/usr/include");
+                     }) != impDirVec.end()) {
+      impDirVec.emplace_back("/usr/include");
+    }
+
     for (std::string const& i : impDirVec) {
       std::string imd = rootPath + i;
       cmSystemTools::ConvertToUnixSlashes(imd);