[clang][cas] Handle include-tree for a file considered part of the module

When building a non-header file with -fmodule-name set, add the
requisite modulemap file even though it is not imported as a module, and
test that we are getting the right semantics for the header include.

Author: benlangmuir

clang/lib/Tooling/DependencyScanning/IncludeTreeActionController.cpp

@@ -486,6 +486,10 @@ IncludeTreeBuilder::finishIncludeTree(CompilerInstance &ScanInstance,
       return std::move(E);
   }
 
+  for (StringRef ModuleMap : FrontendOpts.ModuleMapFiles)
+    if (Error E = addFile(ModuleMap))
+      return std::move(E);
+
   auto FinishIncludeTree = [&]() -> Error {
     IntrusiveRefCntPtr<ASTReader> Reader = ScanInstance.getASTReader();
     if (!Reader)

clang/test/ClangScanDeps/modules-include-tree-implementation.c

@@ -0,0 +1,58 @@
+// REQUIRES: ondisk_cas
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+
+// RUN: clang-scan-deps -compilation-database %t/cdb.json \
+// RUN:   -cas-path %t/cas -module-files-dir %t/outputs \
+// RUN:   -format experimental-include-tree-full -mode preprocess-dependency-directives \
+// RUN:   > %t/deps.json
+
+// RUN: FileCheck %s -input-file %t/deps.json -check-prefix=NO_MODULES
+// NO_MODULES: "modules": []
+
+// RUN: %deps-to-rsp %t/deps.json --tu-index 0 > %t/tu.rsp
+// RUN: cat %t/tu.rsp | sed -E 's|.*"-fcas-include-tree" "(llvmcas://[[:xdigit:]]+)".*|\1|' > %t/tu.casid
+// RUN: clang-cas-test -cas %t/cas -print-include-tree @%t/tu.casid | FileCheck %s -DPREFIX=%/t
+// RUN: %clang @%t/tu.rsp
+
+// CHECK: [[PREFIX]]/tu.c llvmcas://{{[[:xdigit:]]+}}
+// CHECK: 1:1 <built-in> llvmcas://{{[[:xdigit:]]+}}
+
+// Note: this is surprising, but correct: when building the implementation files
+// of a module, the first include is textual but still uses the submodule
+// machinery. The second include is treated as a module import (unless in a PCH)
+// but will not actually import the module only trigger visibility changes.
+
+// CHECK: 2:1 [[PREFIX]]/Mod.h llvmcas://{{[[:xdigit:]]+}}
+// CHECK:   Submodule: Mod
+// CHECK: 3:1 (Module) Mod
+
+// CHECK: Files:
+// CHECK: [[PREFIX]]/tu.c llvmcas://{{[[:xdigit:]]+}}
+// CHECK: [[PREFIX]]/Mod.h llvmcas://{{[[:xdigit:]]+}}
+
+// Despite not importing the module, we need its modulemap for submodule info.
+// CHECK: [[PREFIX]]/module.modulemap llvmcas://{{[[:xdigit:]]+}}
+
+//--- cdb.json.template
+[{
+  "file": "DIR/tu.c",
+  "directory": "DIR",
+  "command": "clang -fsyntax-only DIR/tu.c -I DIR -fmodule-name=Mod -fmodules -fimplicit-modules -fimplicit-module-maps -fmodules-cache-path=DIR/module-cache"
+}]
+
+//--- module.modulemap
+module Mod { header "Mod.h" }
+
+//--- Mod.h
+#pragma once
+void top(void);
+
+//--- tu.c
+#include "Mod.h"
+#include "Mod.h"
+void tu(void) {
+  top();
+}