Reland "[modules] Fix error about the same module being defined in different .pcm files when using VFS overlays."

Fixing Windows buildbot by not using "BuildTemporaries/module.modulemap"
because it is interpreted as defining a module in "BuildTemporaries" directory.

Fix errors like
> module 'MultiPath' is defined in both 'path/to/modules.cache/3JR48BPRU7BCG/MultiPath-1352QHUF8RNMU.pcm' and 'path/to/modules.cache/3JR48BPRU7BCG/MultiPath-20HNSLLIUDDV1.pcm'

To avoid building extra identical modules `-ivfsoverlay` option is not a
part of the hash like "/3JR48BPRU7BCG/". And it is build system's
responsibility to provide `-ivfsoverlay` options that don't cause
observable differences.  We also need to make sure the hash like
"-1352QHUF8RNMU" is not affected by `-ivfsoverlay`. As this hash is
defined by the module map path, use the path prior to any VFS
remappings.

rdar://111921464

Differential Revision: https://reviews.llvm.org/D156749

Author: vsapsai

clang/lib/Lex/HeaderSearch.cpp

@@ -177,7 +177,7 @@ std::string HeaderSearch::getCachedModuleFileName(Module *Module) {
   // *.modulemap file. In this case, just return an empty string.
   if (!ModuleMap)
     return {};
-  return getCachedModuleFileName(Module->Name, ModuleMap->getName());
+  return getCachedModuleFileName(Module->Name, ModuleMap->getNameAsRequested());
 }
 
 std::string HeaderSearch::getPrebuiltModuleFileName(StringRef ModuleName,

clang/lib/Serialization/ASTWriter.cpp

@@ -1327,7 +1327,8 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
 
     auto &Map = PP.getHeaderSearchInfo().getModuleMap();
     AddPath(WritingModule->PresumedModuleMapFile.empty()
-                ? Map.getModuleMapFileForUniquing(WritingModule)->getName()
+                ? Map.getModuleMapFileForUniquing(WritingModule)
+                      ->getNameAsRequested()
                 : StringRef(WritingModule->PresumedModuleMapFile),
             Record);
 

clang/test/VFS/module-map-path.m

@@ -0,0 +1,110 @@
+// Test the module map path is consistent between clang invocations when using VFS overlays.
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// Pre-populate the module cache with the modules that don't use VFS overlays.
+// RUN: %clang_cc1 -fsyntax-only -F%t/Frameworks -I%t/include %t/prepopulate_module_cache.m \
+// RUN:     -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache
+
+// Execute a compilation with VFS overlay. .pcm file path looks like <hash1>/ModuleName-<hash2>.pcm.
+// <hash1> corresponds to the compilation settings like language options.
+// <hash2> corresponds to the module map path. So if any of those change, we should use a different module.
+// But for VFS overlay we make an exception that it's not a part of <hash1> to reduce the number of built .pcm files.
+// Test that paths in overlays don't leak into <hash2> and don't cause using 2 .pcm files for the same module.
+// DEFINE: %{command} = %clang_cc1 -fsyntax-only -verify -F%t/Frameworks -I%t/include %t/test.m \
+// DEFINE:    -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache
+// RUN: sed -e "s@TMP_DIR@%{/t:regex_replacement}@g" -e "s@USE_EXTERNAL_NAMES_OPTION@@g" %t/overlay.yaml.template > %t/external-names-default.yaml
+// RUN: %{command} -ivfsoverlay %t/external-names-default.yaml
+
+// RUN: sed -e "s@TMP_DIR@%{/t:regex_replacement}@g" -e "s@USE_EXTERNAL_NAMES_OPTION@'use-external-names': true,@g" %t/overlay.yaml.template > %t/external-names-true.yaml
+// RUN: %{command} -ivfsoverlay %t/external-names-true.yaml
+
+// RUN: sed -e "s@TMP_DIR@%{/t:regex_replacement}@g" -e "s@USE_EXTERNAL_NAMES_OPTION@'use-external-names': false,@g" %t/overlay.yaml.template > %t/external-names-false.yaml
+// RUN: %{command} -ivfsoverlay %t/external-names-false.yaml
+
+//--- prepopulate_module_cache.m
+#import <Redirecting/Redirecting.h>
+
+//--- test.m
+// At first import multi-path modules directly, so clang decides which .pcm file they should belong to.
+#import <MultiPath/MultiPath.h>
+#import <MultiPathHeader.h>
+
+// Then import a module from the module cache and all its transitive dependencies.
+// Make sure the .pcm files loaded directly are the same as 'Redirecting' is referencing.
+#import <Redirecting/Redirecting.h>
+// expected-no-diagnostics
+
+
+//--- Frameworks/MultiPath.framework/Headers/MultiPath.h
+void multiPathFramework(void);
+
+//--- Frameworks/MultiPath.framework/Modules/module.modulemap
+framework module MultiPath {
+    header "MultiPath.h"
+    export *
+}
+
+
+//--- include/MultiPathHeader.h
+void multiPathHeader(void);
+
+//--- include/module.modulemap
+module MultiPathHeader {
+    header "MultiPathHeader.h"
+    export *
+}
+
+
+//--- Frameworks/Redirecting.framework/Headers/Redirecting.h
+#import <MultiPath/MultiPath.h>
+#import <MultiPathHeader.h>
+
+//--- Frameworks/Redirecting.framework/Modules/module.modulemap
+framework module Redirecting {
+    header "Redirecting.h"
+    export *
+}
+
+
+//--- BuildTemporaries/MultiPath.h
+void multiPathFramework(void);
+//--- BuildTemporaries/framework.modulemap
+framework module MultiPath {
+    header "MultiPath.h"
+    export *
+}
+//--- BuildTemporaries/header.h
+void multiPathHeader(void);
+//--- BuildTemporaries/include.modulemap
+module MultiPathHeader {
+    header "MultiPathHeader.h"
+    export *
+}
+
+//--- overlay.yaml.template
+{
+  'version': 0,
+  USE_EXTERNAL_NAMES_OPTION
+  'roots': [
+    { 'name': 'TMP_DIR/Frameworks/MultiPath.framework/Headers', 'type': 'directory',
+      'contents': [
+        { 'name': 'MultiPath.h', 'type': 'file',
+          'external-contents': 'TMP_DIR/BuildTemporaries/MultiPath.h'}
+    ]},
+    { 'name': 'TMP_DIR/Frameworks/MultiPath.framework/Modules', 'type': 'directory',
+      'contents': [
+        { 'name': 'module.modulemap', 'type': 'file',
+          'external-contents': 'TMP_DIR/BuildTemporaries/framework.modulemap'}
+    ]},
+    { 'name': 'TMP_DIR/include', 'type': 'directory',
+      'contents': [
+        { 'name': 'MultiPathHeader.h', 'type': 'file',
+          'external-contents': 'TMP_DIR/BuildTemporaries/header.h'},
+        { 'name': 'module.modulemap', 'type': 'file',
+          'external-contents': 'TMP_DIR/BuildTemporaries/include.modulemap'}
+    ]}
+  ]
+}
+