[modules] If we have a choice between including a file textually and importing

a prebuilt form from a module, prefer the modular form, all else being equal.

llvm-svn: 229188

1 files changed, 17 insertions, 2 deletions

diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index ef322d8cdc4..529c971ff52 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -314,6 +314,22 @@ void ModuleMap::diagnoseHeaderInclusion(Module *RequestingModule,
   }
 }
 
+static bool isBetterKnownHeader(const ModuleMap::KnownHeader &New,
+                                const ModuleMap::KnownHeader &Old) {
+  // Prefer a public header over a private header.
+  if ((New.getRole() & ModuleMap::PrivateHeader) !=
+      (Old.getRole() & ModuleMap::PrivateHeader))
+    return !(New.getRole() & ModuleMap::PrivateHeader);
+
+  // Prefer a non-textual header over a textual header.
+  if ((New.getRole() & ModuleMap::TextualHeader) !=
+      (Old.getRole() & ModuleMap::TextualHeader))
+    return !(New.getRole() & ModuleMap::TextualHeader);
+
+  // Don't have a reason to choose between these. Just keep the first one.
+  return false;
+}
+
 ModuleMap::KnownHeader
 ModuleMap::findModuleForHeader(const FileEntry *File,
                                Module *RequestingModule,
@@ -348,8 +364,7 @@ ModuleMap::findModuleForHeader(const FileEntry *File,
           !directlyUses(RequestingModule, I->getModule()))
         continue;
 
-      // Prefer a public header over a private header.
-      if (!Result || (Result.getRole() & ModuleMap::PrivateHeader))
+      if (!Result || isBetterKnownHeader(*I, Result))
         Result = *I;
     }
     return MakeResult(Result);