[clang-scan-deps] Infer the target from the executable name (#108189)

This allows clang-scan-deps to work correctly when using cross compilers
with names like <triple>-clang.

Author: mstorsjo

clang/test/ClangScanDeps/implicit-target.c

@@ -0,0 +1,31 @@
+// Check that we can detect an implicit target when clang is invoked as
+// <triple->clang. Using an implicit triple requires that the target actually
+// is available, too.
+// REQUIRES: x86-registered-target
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.in > %t/cdb.json
+
+// Check that we can deduce this both when using a compilation database, and when using
+// a literal command line.
+
+// RUN: clang-scan-deps -format experimental-full -compilation-database %t/cdb.json | FileCheck %s
+
+// RUN: clang-scan-deps -format experimental-full -- x86_64-w64-mingw32-clang %t/source.c -o %t/source.o | FileCheck %s
+
+// CHECK: "-triple",
+// CHECK-NEXT: "x86_64-w64-windows-gnu",
+
+
+//--- cdb.json.in
+[
+  {
+    "directory": "DIR"
+    "command": "x86_64-w64-mingw32-clang -c DIR/source.c -o DIR/source.o"
+    "file": "DIR/source.c"
+  },
+]
+
+//--- source.c
+void func(void) {}

clang/tools/clang-scan-deps/ClangScanDeps.cpp

@@ -15,6 +15,7 @@
 #include "clang/Tooling/DependencyScanning/DependencyScanningTool.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningWorker.h"
 #include "clang/Tooling/JSONCompilationDatabase.h"
+#include "clang/Tooling/Tooling.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CommandLine.h"
@@ -24,6 +25,7 @@
 #include "llvm/Support/LLVMDriver.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/Signals.h"
+#include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/ThreadPool.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/Timer.h"
@@ -795,6 +797,7 @@ getCompilationDatabase(int argc, char **argv, std::string &ErrorMessage) {
 }
 
 int clang_scan_deps_main(int argc, char **argv, const llvm::ToolContext &) {
+  llvm::InitializeAllTargetInfos();
   std::string ErrorMessage;
   std::unique_ptr<tooling::CompilationDatabase> Compilations =
       getCompilationDatabase(argc, argv, ErrorMessage);
@@ -810,6 +813,8 @@ int clang_scan_deps_main(int argc, char **argv, const llvm::ToolContext &) {
   Compilations = expandResponseFiles(std::move(Compilations),
                                      llvm::vfs::getRealFileSystem());
 
+  Compilations = inferTargetAndDriverMode(std::move(Compilations));
+
   // The command options are rewritten to run Clang in preprocessor only mode.
   auto AdjustingCompilations =
       std::make_unique<tooling::ArgumentsAdjustingCompilations>(