[clang][Driver] Support simplified triple versions for config files (#111387)

Currently, the config file system loads the full target triple, e.g.
`arm64-apple-darwin23.6.0.cfg`.

This is however not very useful as this is a moving target. In the case
of macOS, that target moves every ~2 months.

We can improve this by adding fallbacks that simplify the version
component of the triple. This pull request adds support for loading
`arm64-apple-darwin23.cfg` and `arm64-apple-darwin.cfg`. See the
included test for a demonstration on how it works.

Author: Bo98

clang/lib/Driver/Driver.cpp

@@ -1165,6 +1165,34 @@ bool Driver::loadConfigFiles() {
   return false;
 }
 
+static bool findTripleConfigFile(llvm::cl::ExpansionContext &ExpCtx,
+                                 SmallString<128> &ConfigFilePath,
+                                 llvm::Triple Triple, std::string Suffix) {
+  // First, try the full unmodified triple.
+  if (ExpCtx.findConfigFile(Triple.str() + Suffix, ConfigFilePath))
+    return true;
+
+  // Don't continue if we didn't find a parsable version in the triple.
+  VersionTuple OSVersion = Triple.getOSVersion();
+  if (!OSVersion.getMinor().has_value())
+    return false;
+
+  std::string BaseOSName = Triple.getOSTypeName(Triple.getOS()).str();
+
+  // Next try strip the version to only include the major component.
+  // e.g. arm64-apple-darwin23.6.0 -> arm64-apple-darwin23
+  if (OSVersion.getMajor() != 0) {
+    Triple.setOSName(BaseOSName + llvm::utostr(OSVersion.getMajor()));
+    if (ExpCtx.findConfigFile(Triple.str() + Suffix, ConfigFilePath))
+      return true;
+  }
+
+  // Finally, try without any version suffix at all.
+  // e.g. arm64-apple-darwin23.6.0 -> arm64-apple-darwin
+  Triple.setOSName(BaseOSName);
+  return ExpCtx.findConfigFile(Triple.str() + Suffix, ConfigFilePath);
+}
+
 bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
   // Disable default config if CLANG_NO_DEFAULT_CONFIG is set to a non-empty
   // value.
@@ -1176,7 +1204,7 @@ bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
     return false;
 
   std::string RealMode = getExecutableForDriverMode(Mode);
-  std::string Triple;
+  llvm::Triple Triple;
 
   // If name prefix is present, no --target= override was passed via CLOptions
   // and the name prefix is not a valid triple, force it for backwards
@@ -1187,15 +1215,13 @@ bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
     llvm::Triple PrefixTriple{ClangNameParts.TargetPrefix};
     if (PrefixTriple.getArch() == llvm::Triple::UnknownArch ||
         PrefixTriple.isOSUnknown())
-      Triple = PrefixTriple.str();
+      Triple = PrefixTriple;
   }
 
   // Otherwise, use the real triple as used by the driver.
-  if (Triple.empty()) {
-    llvm::Triple RealTriple =
-        computeTargetTriple(*this, TargetTriple, *CLOptions);
-    Triple = RealTriple.str();
-    assert(!Triple.empty());
+  if (Triple.str().empty()) {
+    Triple = computeTargetTriple(*this, TargetTriple, *CLOptions);
+    assert(!Triple.str().empty());
   }
 
   // Search for config files in the following order:
@@ -1210,21 +1236,21 @@ bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
 
   // Try loading <triple>-<mode>.cfg, and return if we find a match.
   SmallString<128> CfgFilePath;
-  std::string CfgFileName = Triple + '-' + RealMode + ".cfg";
-  if (ExpCtx.findConfigFile(CfgFileName, CfgFilePath))
+  if (findTripleConfigFile(ExpCtx, CfgFilePath, Triple,
+                           "-" + RealMode + ".cfg"))
     return readConfigFile(CfgFilePath, ExpCtx);
 
   bool TryModeSuffix = !ClangNameParts.ModeSuffix.empty() &&
                        ClangNameParts.ModeSuffix != RealMode;
   if (TryModeSuffix) {
-    CfgFileName = Triple + '-' + ClangNameParts.ModeSuffix + ".cfg";
-    if (ExpCtx.findConfigFile(CfgFileName, CfgFilePath))
+    if (findTripleConfigFile(ExpCtx, CfgFilePath, Triple,
+                             "-" + ClangNameParts.ModeSuffix + ".cfg"))
       return readConfigFile(CfgFilePath, ExpCtx);
   }
 
   // Try loading <mode>.cfg, and return if loading failed.  If a matching file
   // was not found, still proceed on to try <triple>.cfg.
-  CfgFileName = RealMode + ".cfg";
+  std::string CfgFileName = RealMode + ".cfg";
   if (ExpCtx.findConfigFile(CfgFileName, CfgFilePath)) {
     if (readConfigFile(CfgFilePath, ExpCtx))
       return true;
@@ -1236,8 +1262,7 @@ bool Driver::loadDefaultConfigFiles(llvm::cl::ExpansionContext &ExpCtx) {
   }
 
   // Try loading <triple>.cfg and return if we find a match.
-  CfgFileName = Triple + ".cfg";
-  if (ExpCtx.findConfigFile(CfgFileName, CfgFilePath))
+  if (findTripleConfigFile(ExpCtx, CfgFilePath, Triple, ".cfg"))
     return readConfigFile(CfgFilePath, ExpCtx);
 
   // If we were unable to find a config file deduced from executable name,

clang/test/Driver/config-file3.c

@@ -226,3 +226,26 @@
 //
 // RUN: HOME=%S/Inputs/config %clang -### --config-user-dir=~ -v 2>&1 | FileCheck %s --check-prefix=CHECK-TILDE
 // CHECK-TILDE: User configuration file directory: {{.*}}/Inputs/config
+
+//--- Fallback to stripping OS versions
+//
+// RUN: touch %t/testdmode/x86_64-apple-darwin23.6.0-clang.cfg
+// RUN: touch %t/testdmode/x86_64-apple-darwin23-clang.cfg
+// RUN: touch %t/testdmode/x86_64-apple-darwin-clang.cfg
+// RUN: %clang -target x86_64-apple-darwin23.6.0 --config-system-dir=%t/testdmode --config-user-dir= -no-canonical-prefixes --version 2>&1 | FileCheck %s -check-prefix DARWIN --implicit-check-not 'Configuration file:'
+//
+// DARWIN: Configuration file: {{.*}}/testdmode/x86_64-apple-darwin23.6.0-clang.cfg
+
+//--- DARWIN + no full version
+//
+// RUN: rm %t/testdmode/x86_64-apple-darwin23.6.0-clang.cfg
+// RUN: %clang -target x86_64-apple-darwin23.6.0 --config-system-dir=%t/testdmode --config-user-dir= -no-canonical-prefixes --version 2>&1 | FileCheck %s -check-prefix DARWIN-MAJOR --implicit-check-not 'Configuration file:'
+//
+// DARWIN-MAJOR: Configuration file: {{.*}}/testdmode/x86_64-apple-darwin23-clang.cfg
+
+//--- DARWIN + no version
+//
+// RUN: rm %t/testdmode/x86_64-apple-darwin23-clang.cfg
+// RUN: %clang -target x86_64-apple-darwin23.6.0 --config-system-dir=%t/testdmode --config-user-dir= -no-canonical-prefixes --version 2>&1 | FileCheck %s -check-prefix DARWIN-VERSIONLESS --implicit-check-not 'Configuration file:'
+//
+// DARWIN-VERSIONLESS: Configuration file: {{.*}}/testdmode/x86_64-apple-darwin-clang.cfg