[clang] [flang] [flang][Driver] Better error message when multiple actions are specified (PR #165575)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu created https://github.com/llvm/llvm-project/pull/165575

List all the action options that were provided in the error message emitted when multiple actions are specified

Fixes #79458

>From 374bcb17b2bf4527e0863a3c51c55c4b89048501 Mon Sep 17 00:00:00 2001
From: Tarun Prabhu <tarun.prabhu at gmail.com>
Date: Tue, 28 Oct 2025 21:32:22 -0600
Subject: [PATCH] [flang][Driver] Better error message when multiple actions
 are specified

List all the action options that were provided in the error message emitted when
multiple actions are specified

Fixes #79458
---
 .../clang/Basic/DiagnosticDriverKinds.td      |  2 +
 flang/lib/Frontend/CompilerInvocation.cpp     | 15 ++++++--
 flang/test/Driver/multiple-actions-error.f95  | 38 +++++++++++++++----
 3 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index 83980e3ac35b7..2fefe1dbe0dd6 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -312,6 +312,8 @@ def warn_drv_yc_multiple_inputs_clang_cl : Warning<
 def warn_drv_potentially_misspelled_joined_argument : Warning<
   "joined argument treated as '%0'; did you mean '%1'?">, InGroup<UnknownArgument>;
 
+def err_drv_too_many_actions: Error<
+    "only one action option is allowed. Got '%0'">;
 def err_drv_invalid_value : Error<"invalid value '%1' in '%0'">;
 def err_drv_invalid_int_value : Error<"invalid integral value '%1' in '%0'">;
 def err_drv_invalid_value_with_suggestion : Error<
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index 548ca675db5ea..d7bdbc121274d 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -595,9 +595,18 @@ static bool parseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
   // -cc1` does accept multiple action options, but will only consider the
   // rightmost one.
   if (args.hasMultipleArgs(clang::driver::options::OPT_Action_Group)) {
-    const unsigned diagID = diags.getCustomDiagID(
-        clang::DiagnosticsEngine::Error, "Only one action option is allowed");
-    diags.Report(diagID);
+    llvm::SmallString<32> buf;
+    llvm::raw_svector_ostream os(buf);
+    for (const llvm::opt::Arg *arg :
+         args.filtered(clang::driver::options::OPT_Action_Group)) {
+      if (buf.size())
+        os << ", ";
+      os << "'" << arg->getSpelling() << "'";
+    }
+    // The diagnostics engine will add single quotes around the argument to the
+    // error message. Strip the leading and trailing quote from here.
+    diags.Report(clang::diag::err_drv_too_many_actions)
+        << buf.substr(1, buf.size() - 2);
     return false;
   }
 
diff --git a/flang/test/Driver/multiple-actions-error.f95 b/flang/test/Driver/multiple-actions-error.f95
index 5ec4e9166657f..3b2b7dc26d2c6 100644
--- a/flang/test/Driver/multiple-actions-error.f95
+++ b/flang/test/Driver/multiple-actions-error.f95
@@ -1,8 +1,30 @@
-! Verify that the frontend driver error-out if multiple actions are specified
-
-! RUN: not %flang_fc1 -E -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix=ERROR
-! RUN: not %flang_fc1 -fsyntax-only -fsyntax-only %s 2>&1 | FileCheck %s --check-prefix=ERROR
-
-! ERROR: error: Only one action option is allowed
-
-end progream
+! Verify that the frontend driver raises the expected error when multiple
+! actions are specified.
+!
+! RUN: not %flang_fc1 -fsyntax-only -fsyntax-only %s 2>&1 \
+! RUN:     | FileCheck %s --check-prefixes=ERROR,ACTIONS-1
+!
+! RUN: not %flang_fc1 -E -fsyntax-only %s 2>&1 \
+! RUN:     | FileCheck %s --check-prefixes=ERROR,ACTIONS-2
+!
+! RUN: not %flang_fc1 -fsyntax-only -E -emit-llvm %s 2>&1 \
+! RUN:     | FileCheck %s --check-prefixes=ERROR,ACTIONS-3
+!
+! If one or more options are specified with -Xflang, they will appear last in
+! the error message.
+!
+! RUN: not %flang -S -Xflang -emit-llvm %s 2>&1 \
+! RUN:     | FileCheck %s --check-prefixes=ERROR,ACTIONS-4
+!
+! RUN: not %flang -Xflang -emit-llvm -S %s 2>&1 \
+! RUN:     | FileCheck %s --check-prefixes=ERROR,ACTIONS-4
+!
+! RUN: not %flang -Xflang -emit-obj -S -Xflang -emit-llvm %s 2>&1 \
+! RUN:     | FileCheck %s --check-prefixes=ERROR,ACTIONS-5
+!
+! ERROR: error: only one action option is allowed.
+! ACTIONS-1: Got '-fsyntax-only', '-fsyntax-only'
+! ACTIONS-2: Got '-E', '-fsyntax-only'
+! ACTIONS-3: Got '-fsyntax-only', '-E', '-emit-llvm'
+! ACTIONS-4: Got '-S', '-emit-llvm'
+! ACTIONS-5: Got '-S', '-emit-obj', '-emit-llvm'