Reland "[clang][driver] Emit a warning if -xc/-xc++ is after the last…

… input file" This reverts commit ba59476.
llvm · Mar 17, 2022 · e2a1f8e · e2a1f8e
1 parent 34ce42f
commit e2a1f8e
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diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -365,6 +365,9 @@ def warn_drv_preprocessed_input_file_unused : Warning<
 def warn_drv_unused_argument : Warning<
   "argument unused during compilation: '%0'">,
   InGroup<UnusedCommandLineArgument>;
+def warn_drv_unused_x : Warning<
+  "'-x %0' after last input file has no effect">,
+  InGroup<UnusedCommandLineArgument>;
 def warn_drv_empty_joined_argument : Warning<
   "joined argument expects additional value: '%0'">,
   InGroup<UnusedCommandLineArgument>;

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
@@ -2308,6 +2308,14 @@ void Driver::BuildInputs(const ToolChain &TC, DerivedArgList &Args,
     assert(!Args.hasArg(options::OPT_x) && "-x and /TC or /TP is not allowed");
   }
 
+  // Warn -x after last input file has no effect
+  {
+    Arg *LastXArg = Args.getLastArgNoClaim(options::OPT_x);
+    Arg *LastInputArg = Args.getLastArgNoClaim(options::OPT_INPUT);
+    if (LastXArg && LastInputArg && LastInputArg->getIndex() < LastXArg->getIndex())
+      Diag(clang::diag::warn_drv_unused_x) << LastXArg->getValue();
+  }
+
   for (Arg *A : Args) {
     if (A->getOption().getKind() == Option::InputClass) {
       const char *Value = A->getValue();

diff --git a/clang/test/Driver/x-args.c b/clang/test/Driver/x-args.c
@@ -0,0 +1,7 @@
+// RUN: %clang -fsyntax-only -Werror -xc %s
+// RUN: %clang -fsyntax-only -Werror %s -xc %s
+
+// RUN: %clang -fsyntax-only %s -xc++ -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -fsyntax-only -xc %s -xc++ -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -fsyntax-only %s -xc %s -xc++ -fsyntax-only 2>&1 | FileCheck %s
+// CHECK: '-x c++' after last input file has no effect