[Support] Expand `<CFGDIR>` as the base directory in configuration files.

Extends response file expansion to recognize `<CFGDIR>` and expand to the
current file's directory. This makes it much easier to author clang config
files rooted in portable, potentially not-installed SDK directories.

A typical use case may be something like the following:

```
# sample_sdk.cfg
--target=sample
-isystem <CFGDIR>/include
-L <CFGDIR>/lib
-T <CFGDIR>/ldscripts/link.ld
```

Reviewed By: sepavloff

Differential Revision: https://reviews.llvm.org/D115604

1 files changed, 58 insertions, 16 deletions

diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index 4153a69..481ba56 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -1078,11 +1078,45 @@ static bool hasUTF8ByteOrderMark(ArrayRef<char> S) {
   return (S.size() >= 3 && S[0] == '\xef' && S[1] == '\xbb' && S[2] == '\xbf');
 }
 
+// Substitute <CFGDIR> with the file's base path.
+static void ExpandBasePaths(StringRef BasePath, StringSaver &Saver,
+                            const char *&Arg) {
+  assert(sys::path::is_absolute(BasePath));
+  constexpr StringLiteral Token("<CFGDIR>");
+  const StringRef ArgString(Arg);
+
+  SmallString<128> ResponseFile;
+  StringRef::size_type StartPos = 0;
+  for (StringRef::size_type TokenPos = ArgString.find(Token);
+       TokenPos != StringRef::npos;
+       TokenPos = ArgString.find(Token, StartPos)) {
+    // Token may appear more than once per arg (e.g. comma-separated linker
+    // args). Support by using path-append on any subsequent appearances.
+    const StringRef LHS = ArgString.substr(StartPos, TokenPos - StartPos);
+    if (ResponseFile.empty())
+      ResponseFile = LHS;
+    else
+      llvm::sys::path::append(ResponseFile, LHS);
+    ResponseFile.append(BasePath);
+    StartPos = TokenPos + Token.size();
+  }
+
+  if (!ResponseFile.empty()) {
+    // Path-append the remaining arg substring if at least one token appeared.
+    const StringRef Remaining = ArgString.substr(StartPos);
+    if (!Remaining.empty())
+      llvm::sys::path::append(ResponseFile, Remaining);
+    Arg = Saver.save(ResponseFile.str()).data();
+  }
+}
+
 // FName must be an absolute path.
-static llvm::Error ExpandResponseFile(
-    StringRef FName, StringSaver &Saver, TokenizerCallback Tokenizer,
-    SmallVectorImpl<const char *> &NewArgv, bool MarkEOLs, bool RelativeNames,
-    llvm::vfs::FileSystem &FS) {
+static llvm::Error ExpandResponseFile(StringRef FName, StringSaver &Saver,
+                                      TokenizerCallback Tokenizer,
+                                      SmallVectorImpl<const char *> &NewArgv,
+                                      bool MarkEOLs, bool RelativeNames,
+                                      bool ExpandBasePath,
+                                      llvm::vfs::FileSystem &FS) {
   assert(sys::path::is_absolute(FName));
   llvm::ErrorOr<std::unique_ptr<MemoryBuffer>> MemBufOrErr =
       FS.getBufferForFile(FName);
@@ -1116,8 +1150,15 @@ static llvm::Error ExpandResponseFile(
   // file, replace the included response file names with their full paths
   // obtained by required resolution.
   for (auto &Arg : NewArgv) {
+    if (!Arg)
+      continue;
+
+    // Substitute <CFGDIR> with the file's base path.
+    if (ExpandBasePath)
+      ExpandBasePaths(BasePath, Saver, Arg);
+
     // Skip non-rsp file arguments.
-    if (!Arg || Arg[0] != '@')
+    if (Arg[0] != '@')
       continue;
 
     StringRef FileName(Arg + 1);
@@ -1129,7 +1170,7 @@ static llvm::Error ExpandResponseFile(
     ResponseFile.push_back('@');
     ResponseFile.append(BasePath);
     llvm::sys::path::append(ResponseFile, FileName);
-    Arg = Saver.save(ResponseFile.c_str()).data();
+    Arg = Saver.save(ResponseFile.str()).data();
   }
   return Error::success();
 }
@@ -1138,7 +1179,7 @@ static llvm::Error ExpandResponseFile(
 /// StringSaver and tokenization strategy.
 bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                              SmallVectorImpl<const char *> &Argv, bool MarkEOLs,
-                             bool RelativeNames,
+                             bool RelativeNames, bool ExpandBasePath,
                              llvm::Optional<llvm::StringRef> CurrentDir,
                              llvm::vfs::FileSystem &FS) {
   bool AllExpanded = true;
@@ -1218,7 +1259,7 @@ bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
     SmallVector<const char *, 0> ExpandedArgv;
     if (llvm::Error Err =
             ExpandResponseFile(FName, Saver, Tokenizer, ExpandedArgv, MarkEOLs,
-                               RelativeNames, FS)) {
+                               RelativeNames, ExpandBasePath, FS)) {
       // We couldn't read this file, so we leave it in the argument stream and
       // move on.
       // TODO: The error should be propagated up the stack.
@@ -1250,11 +1291,11 @@ bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
 
 bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                              SmallVectorImpl<const char *> &Argv, bool MarkEOLs,
-                             bool RelativeNames,
+                             bool RelativeNames, bool ExpandBasePath,
                              llvm::Optional<StringRef> CurrentDir) {
   return ExpandResponseFiles(Saver, std::move(Tokenizer), Argv, MarkEOLs,
-                             RelativeNames, std::move(CurrentDir),
-                             *vfs::getRealFileSystem());
+                             RelativeNames, ExpandBasePath,
+                             std::move(CurrentDir), *vfs::getRealFileSystem());
 }
 
 bool cl::expandResponseFiles(int Argc, const char *const *Argv,
@@ -1281,16 +1322,17 @@ bool cl::readConfigFile(StringRef CfgFile, StringSaver &Saver,
     llvm::sys::path::append(AbsPath, CfgFile);
     CfgFile = AbsPath.str();
   }
-  if (llvm::Error Err =
-          ExpandResponseFile(CfgFile, Saver, cl::tokenizeConfigFile, Argv,
-                             /*MarkEOLs=*/false, /*RelativeNames=*/true,
-                             *llvm::vfs::getRealFileSystem())) {
+  if (llvm::Error Err = ExpandResponseFile(
+          CfgFile, Saver, cl::tokenizeConfigFile, Argv,
+          /*MarkEOLs=*/false, /*RelativeNames=*/true, /*ExpandBasePath=*/true,
+          *llvm::vfs::getRealFileSystem())) {
     // TODO: The error should be propagated up the stack.
     llvm::consumeError(std::move(Err));
     return false;
   }
   return ExpandResponseFiles(Saver, cl::tokenizeConfigFile, Argv,
-                             /*MarkEOLs=*/false, /*RelativeNames=*/true);
+                             /*MarkEOLs=*/false, /*RelativeNames=*/true,
+                             /*ExpandBasePath=*/true, llvm::None);
 }
 
 static void initCommonOptions();