[Dependency Scanning] Add option to specify a separate Clang Dependency scanner module cache.

Clang dependency scanning produces scanner PCMs which we may want to live in a
different filesystem location than the main build module cache.

Resolves rdar://113222853

Author: artemcm

include/swift/Basic/LangOptions.h

@@ -811,6 +811,9 @@ namespace swift {
     /// The module cache path which the Clang importer should use.
     std::string ModuleCachePath;
 
+    /// The Scanning module cache path which the Clang Dependency Scanner should use.
+    std::string ClangScannerModuleCachePath;
+
     /// Extra arguments which should be passed to the Clang importer.
     std::vector<std::string> ExtraArgs;
 

include/swift/Frontend/Frontend.h

@@ -168,10 +168,18 @@ class CompilerInvocation {
     ClangImporterOpts.ModuleCachePath = Path.str();
   }
 
+  void setClangScannerModuleCachePath(StringRef Path) {
+    ClangImporterOpts.ClangScannerModuleCachePath = Path.str();
+  }
+
   StringRef getClangModuleCachePath() const {
     return ClangImporterOpts.ModuleCachePath;
   }
 
+  StringRef getClangScannerModuleCachePath() const {
+    return ClangImporterOpts.ClangScannerModuleCachePath;
+  }
+
   void setImportSearchPaths(const std::vector<std::string> &Paths) {
     SearchPathOpts.setImportSearchPaths(Paths);
   }

include/swift/Option/Options.td

@@ -1838,6 +1838,9 @@ def cas_plugin_option: Separate<["-"], "cas-plugin-option">,
   Flags<[FrontendOption, NewDriverOnlyOption]>,
   HelpText<"Option pass to CAS Plugin">, MetaVarName<"<name>=<option>">;
 
+def clang_scanner_module_cache_path : Separate<["-"], "clang-scanner-module-cache-path">,
+  Flags<[FrontendOption, DoesNotAffectIncrementalBuild, ArgumentIsPath]>,
+  HelpText<"Specifies the Clang dependency scanner module cache path">;
 
 // END ONLY SUPPORTED IN NEW DRIVER
 

lib/ClangImporter/ClangImporter.cpp

@@ -667,7 +667,13 @@ importer::getNormalInvocationArguments(
   }
 
   const std::string &moduleCachePath = importerOpts.ModuleCachePath;
-  if (!moduleCachePath.empty() && !importerOpts.DisableImplicitClangModules) {
+  const std::string &scannerCachePath = importerOpts.ClangScannerModuleCachePath;
+  // If a scanner cache is specified, this must be a scanning action. Prefer this
+  // path for the Clang scanner to cache its Scanning PCMs.
+  if (!scannerCachePath.empty()) {
+    invocationArgStrs.push_back("-fmodules-cache-path=");
+    invocationArgStrs.back().append(scannerCachePath);
+  } else if (!moduleCachePath.empty() && !importerOpts.DisableImplicitClangModules) {
     invocationArgStrs.push_back("-fmodules-cache-path=");
     invocationArgStrs.back().append(moduleCachePath);
   }

lib/Frontend/CompilerInvocation.cpp

@@ -1461,6 +1461,9 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts,
   if (const Arg *A = Args.getLastArg(OPT_module_cache_path)) {
     Opts.ModuleCachePath = A->getValue();
   }
+  if (const Arg *A = Args.getLastArg(OPT_clang_scanner_module_cache_path)) {
+    Opts.ClangScannerModuleCachePath = A->getValue();
+  }
 
   if (const Arg *A = Args.getLastArg(OPT_target_cpu))
     Opts.TargetCPU = A->getValue();

test/ScanDependencies/separate_clang_scan_cache.swift

@@ -0,0 +1,15 @@
+// RUN: %empty-directory(%t.module-cache)
+// RUN: %empty-directory(%t.scanner-cache)
+
+// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t.module-cache -clang-scanner-module-cache-path %t.scanner-cache %s -o %t.deps.json -I %S/Inputs/SwiftDifferent -dump-clang-diagnostics 2>&1 | %FileCheck %s --check-prefix=CHECK-CLANG-COMMAND
+// RUN: %validate-json %t.deps.json | %FileCheck %s --check-prefix=CHECK-DEPS
+
+// CHECK-CLANG-COMMAND: '-fmodules-cache-path={{.*}}.scanner-cache'
+
+// CHECK-DEPS: "swift": "A"
+// CHECK-DEPS:            "swift": "A"
+// CHECK-DEPS-NEXT:    },
+// CHECK-DEPS-NEXT:    {
+// CHECK-DEPS-NEXT:        "modulePath": "{{.*}}.module-cache/A-{{.*}}.swiftmodule",
+// CHECK-DEPS-NEXT:      "sourceFiles": [
+import A