Set up MSVC environment for C preprocessing on Windows

CHANGELOG.md

@@ -4,7 +4,7 @@
 - Frontend, druntime and Phobos are at version [2.103.1](https://dlang.org/changelog/2.103.0.html), incl. new command-line option `-verror-supplements`. (#4345)
 - New commandline option `-femit-local-var-lifetime` that enables variable lifetime (scope) annotation to LLVM IR codegen. Lifetime annotation enables stack memory reuse for local variables with non-overlapping scope. (#4395)
 - C files are now automatically preprocessed using the external C compiler (configurable via `-gcc` or the `CC` environment variable, and `-Xcc` for extra flags). Extra preprocessor flags (e.g., include dirs and manual defines) can be added via new command-line option `-P`. (#4417)
-  - Windows: Requires an MSVC environment set up for the target (`cl.exe` on `PATH`, `INCLUDE` environment variable). If `clang-cl.exe` is on `PATH`, it is preferred over Microsoft's `cl.exe` by default (e.g., to avoid printing the C source file path to stderr during preprocessing).
+  - Windows: If `clang-cl.exe` is on `PATH`, it is preferred over Microsoft's `cl.exe` by default (e.g., to avoid printing the C source file path to stderr during preprocessing).
 
 #### Platform support
 

dmd/vsoptions.d

@@ -486,6 +486,21 @@ public:
         return FileName.exists(proposed) ? proposed : null;
     }
 
+version (IN_LLVM)
+{
+    const(char)* getVCIncludeDir() const
+    {
+        const(char)* proposed;
+
+        if (VCToolsInstallDir !is null)
+            proposed = FileName.combine(VCToolsInstallDir, "include");
+        else if (VCInstallDir !is null)
+            proposed = FileName.combine(VCInstallDir, "include");
+
+        return FileName.exists(proposed) ? proposed : null;
+    }
+}
+
     /**
      * get the path to the universal CRT libraries
      * Params:
@@ -546,6 +561,33 @@ version (IN_LLVM) {} else
         return null;
     }
 
+version (IN_LLVM)
+{
+    const(char)* getSDKIncludePath() const
+    {
+        if (WindowsSdkDir)
+        {
+            alias umExists = returnDirIfContainsFile!"um"; // subdir in this case
+
+            const sdk = FileName.combine(WindowsSdkDir.toDString, "include");
+            if (WindowsSdkVersion)
+            {
+                if (auto p = umExists(sdk, WindowsSdkVersion.toDString)) // SDK 10.0
+                    return p;
+            }
+            // purely speculative
+            if (auto p = umExists(sdk, "win8")) // SDK 8.0
+                return p;
+            if (auto p = umExists(sdk, "winv6.3")) // SDK 8.1
+                return p;
+            if (auto p = umExists(sdk)) // SDK 7.1 or earlier
+                return p;
+        }
+
+        return null;
+    }
+}
+
 private:
 extern(D):
 

dmd/vsoptions.h

@@ -25,8 +25,14 @@ struct VSOptions
     void initialize();
     const char *getVCBinDir(bool x64, const char *&addpath) const;
     const char *getVCLibDir(bool x64) const;
+#if IN_LLVM
+    const char *getVCIncludeDir() const;
+#endif
     const char *getUCRTLibPath(bool x64) const;
     const char *getSDKLibPath(bool x64) const;
+#if IN_LLVM
+    const char *getSDKIncludePath() const;
+#endif
 };
 
 #endif // _WIN32

driver/cpreprocessor.cpp

@@ -73,11 +73,10 @@ FileName runCPreprocessor(FileName csrcfile, const Loc &loc, bool &ifile,
   const auto &triple = *global.params.targetTriple;
   const bool isMSVC = triple.isWindowsMSVCEnvironment();
 
-#if 0 //ifdef _WIN32
+#ifdef _WIN32
-  // TODO: INCLUDE env var etc.?
   windows::MsvcEnvironmentScope msvcEnv;
   if (isMSVC)
-    msvcEnv.setup();
+    msvcEnv.setup(/*forPreprocessingOnly=*/true);
 #endif
 
   FileName ipath = getOutputPath(loc, csrcfile.toChars());

driver/tool.cpp

@@ -265,7 +265,10 @@ int executeToolAndWait(const Loc &loc, const std::string &tool_,
 namespace windows {
 
 namespace {
+VSOptions vsOptions; // cache, as this can be expensive
+
 bool setupMsvcEnvironmentImpl(
+    bool forPreprocessingOnly,
     std::vector<std::pair<std::wstring, wchar_t *>> *rollback) {
   const bool x64 = global.params.targetTriple->isArch64Bit();
 
@@ -280,19 +283,13 @@ bool setupMsvcEnvironmentImpl(
 
   const auto begin = std::chrono::steady_clock::now();
 
-  VSOptions vsOptions;
+  if (!vsOptions.VSInstallDir) {
-  vsOptions.initialize();
+    vsOptions.initialize();
-  if (!vsOptions.VSInstallDir)
+    if (!vsOptions.VSInstallDir)
-    return false;
+      return false;
-
+  }
-  llvm::SmallVector<const char *, 3> libPaths;
-  if (auto vclibdir = vsOptions.getVCLibDir(x64))
-    libPaths.push_back(vclibdir);
-  if (auto ucrtlibdir = vsOptions.getUCRTLibPath(x64))
-    libPaths.push_back(ucrtlibdir);
-  if (auto sdklibdir = vsOptions.getSDKLibPath(x64))
-    libPaths.push_back(sdklibdir);
 
+  // PATH
   llvm::SmallVector<const char *, 2> binPaths;
   const char *secondaryBindir = nullptr;
   if (auto bindir = vsOptions.getVCBinDir(x64, secondaryBindir)) {
@@ -300,20 +297,52 @@ bool setupMsvcEnvironmentImpl(
     if (secondaryBindir)
       binPaths.push_back(secondaryBindir);
   }
-
+  if (binPaths.empty())
-  const bool success = libPaths.size() == 3 && !binPaths.empty();
-  if (!success)
     return false;
 
+  llvm::SmallVector<const char *, 3> includePaths;
+  llvm::SmallVector<const char *, 3> libPaths;
+  if (forPreprocessingOnly) {
+    // INCLUDE
+    if (auto vcincludedir = vsOptions.getVCIncludeDir()) {
+      includePaths.push_back(vcincludedir);
+    } else {
+      return false;
+    }
+    if (auto sdkincludedir = vsOptions.getSDKIncludePath()) {
+      includePaths.push_back(FileName::combine(sdkincludedir, "ucrt"));
+      includePaths.push_back(FileName::combine(sdkincludedir, "shared"));
+      includePaths.push_back(FileName::combine(sdkincludedir, "um"));
+      includePaths.push_back(FileName::combine(sdkincludedir, "winrt"));
+      includePaths.push_back(FileName::combine(sdkincludedir, "cppwinrt"));
+    } else {
+      return false;
+    }
+  } else {
+    // LIB
+    if (auto vclibdir = vsOptions.getVCLibDir(x64))
+      libPaths.push_back(vclibdir);
+    if (auto ucrtlibdir = vsOptions.getUCRTLibPath(x64))
+      libPaths.push_back(ucrtlibdir);
+    if (auto sdklibdir = vsOptions.getSDKLibPath(x64))
+      libPaths.push_back(sdklibdir);
+
+    if (libPaths.size() != 3)
+      return false;
+  }
+
   if (!rollback) // check for availability only
     return true;
 
   if (global.params.verbose)
     message("Prepending to environment variables:");
 
-  const auto preprendToEnvVar =
+  const auto prependToEnvVar =
       [rollback](const char *key, const wchar_t *wkey,
                  const llvm::SmallVectorImpl<const char *> &entries) {
+        if (entries.empty())
+          return;
+
         wchar_t *originalValue = _wgetenv(wkey);
 
         llvm::SmallString<256> head;
@@ -343,8 +372,9 @@ bool setupMsvcEnvironmentImpl(
       };
 
   rollback->reserve(2);
-  preprendToEnvVar("LIB", L"LIB", libPaths);
+  prependToEnvVar("INCLUDE", L"INCLUDE", includePaths);
-  preprendToEnvVar("PATH", L"PATH", binPaths);
+  prependToEnvVar("LIB", L"LIB", libPaths);
+  prependToEnvVar("PATH", L"PATH", binPaths);
 
   if (global.params.verbose) {
     const auto end = std::chrono::steady_clock::now();
@@ -357,11 +387,11 @@ bool setupMsvcEnvironmentImpl(
 }
 } // anonymous namespace
 
-bool isMsvcAvailable() { return setupMsvcEnvironmentImpl(nullptr); }
+bool isMsvcAvailable() { return setupMsvcEnvironmentImpl(false, nullptr); }
 
-bool MsvcEnvironmentScope::setup() {
+bool MsvcEnvironmentScope::setup(bool forPreprocessingOnly) {
   rollback.clear();
-  return setupMsvcEnvironmentImpl(&rollback);
+  return setupMsvcEnvironmentImpl(forPreprocessingOnly, &rollback);
 }
 
 MsvcEnvironmentScope::~MsvcEnvironmentScope() {

driver/tool.h

@@ -53,7 +53,7 @@ struct MsvcEnvironmentScope {
   // Tries to set up the MSVC environment variables for the current process and
   // returns true if successful. The original environment is restored on
   // destruction.
-  bool setup();
+  bool setup(bool forPreprocessingOnly = false);
 
   ~MsvcEnvironmentScope();