[clang] [flang] [flang][driver] Use -Xflang in diagnostics (PR #164741)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu updated https://github.com/llvm/llvm-project/pull/164741

>From 6772340ecb8193099c4332e7f84518c9b9f8de6d Mon Sep 17 00:00:00 2001
From: Tarun Prabhu <tarun.prabhu at gmail.com>
Date: Wed, 22 Oct 2025 19:29:35 -0600
Subject: [PATCH 1/3] [flang][driver] Use -Xflang in diagnostics

When an option that is only available in `flang -fc1` is provided to `flang`,
emit a diagnostic with a suggestion containing "did you mean -Xflang '-foo'".

Partially addresses #163550.
---
 clang/lib/Driver/Driver.cpp        | 11 ++++++++++-
 flang/test/Driver/flang-f-opts.f90 | 21 +++++++++++++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 40ea513e85427..afaf6c2691ac6 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -308,7 +308,16 @@ InputArgList Driver::ParseArgStrings(ArrayRef<const char *> ArgStrings,
     auto ArgString = A->getAsString(Args);
     std::string Nearest;
     if (getOpts().findNearest(ArgString, Nearest, VisibilityMask) > 1) {
-      if (!IsCLMode() &&
+      if (IsFlangMode()) {
+        if (getOpts().findExact(ArgString, Nearest,
+                                llvm::opt::Visibility(options::FC1Option))) {
+          DiagID = diag::err_drv_unknown_argument_with_suggestion;
+          Diags.Report(DiagID) << ArgString << "-Xflang " + Nearest;
+        } else {
+          DiagID = diag::err_drv_unknown_argument;
+          Diags.Report(DiagID) << ArgString;
+        }
+      } else if (!IsCLMode() &&
           getOpts().findExact(ArgString, Nearest,
                               llvm::opt::Visibility(options::CC1Option))) {
         DiagID = diag::err_drv_unknown_argument_with_suggestion;
diff --git a/flang/test/Driver/flang-f-opts.f90 b/flang/test/Driver/flang-f-opts.f90
index 77bb4d7aa8a91..0fbfa5c0b05d6 100644
--- a/flang/test/Driver/flang-f-opts.f90
+++ b/flang/test/Driver/flang-f-opts.f90
@@ -1,5 +1,5 @@
-! Test for warnings generated when parsing driver options. You can use this file for relatively small tests and to avoid creating
-! new test files.
+! Test for errors and warnings generated when parsing driver options. You can
+! use this file for relatively small tests and to avoid creating new test files.
 
 ! RUN: %flang -### -S -O4 -ffp-contract=on %s 2>&1 | FileCheck %s
 
@@ -26,3 +26,20 @@
 ! RUN:     | FileCheck %s -check-prefix=WARN-BUILTIN-MULTIPLE
 ! WARN-BUILTIN-MULTIPLE: warning: '-fbuiltin' is not valid for Fortran
 ! WARN-BUILTIN-MULTIPLE: warning: '-fno-builtin' is not valid for Fortran
+
+! When issuing a warning with a suggestion, ensure that the suggestion uses
+! "-Xflang" in the diagnostic message. This is typically issued when an option
+! that is available for `flang -fc1` is passed to `flang`. We use -complex-range
+! since it is only available for fc1. If this option is ever exposed to `flang`,
+! a different option will have to be used in the test below.
+!
+! RUN: not %flang -### -complex-range=full %s 2>&1 \
+! RUN:     | FileCheck %s -check-prefix UNKNOWN-SUGGEST
+!
+! UNKNOWN-SUGGEST: error: unknown argument '-complex-range=full';
+! UNKNOWN-SUGGEST-SAME: did you mean '-Xflang -complex-range=full'
+!
+! RUN: not %flang -### -not-an-option %s 2>&1 \
+! RUN:     | FileCheck %s -check-prefix UNKNOWN-NO-SUGGEST
+!
+! UNKNOWN-NO-SUGGEST: error: unknown argument: '-not-an-option'{{$}}

>From 24a1b19f9141e47e872174a2c73b989b6bd7ee2e Mon Sep 17 00:00:00 2001
From: Tarun Prabhu <tarun.prabhu at gmail.com>
Date: Wed, 22 Oct 2025 19:37:33 -0600
Subject: [PATCH 2/3] Improve clarity of comment

---
 flang/test/Driver/flang-f-opts.f90 | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/flang/test/Driver/flang-f-opts.f90 b/flang/test/Driver/flang-f-opts.f90
index 0fbfa5c0b05d6..9ef0abaa176f0 100644
--- a/flang/test/Driver/flang-f-opts.f90
+++ b/flang/test/Driver/flang-f-opts.f90
@@ -27,8 +27,8 @@
 ! WARN-BUILTIN-MULTIPLE: warning: '-fbuiltin' is not valid for Fortran
 ! WARN-BUILTIN-MULTIPLE: warning: '-fno-builtin' is not valid for Fortran
 
-! When issuing a warning with a suggestion, ensure that the suggestion uses
-! "-Xflang" in the diagnostic message. This is typically issued when an option
+! When emitting an error with a suggestion, ensure that the diagnostic message
+! uses '-Xflang' instead of '-Xclang'. This is typically emitted when an option
 ! that is available for `flang -fc1` is passed to `flang`. We use -complex-range
 ! since it is only available for fc1. If this option is ever exposed to `flang`,
 ! a different option will have to be used in the test below.

>From abc5c77393f4fbe742383febf843bfda24100a8d Mon Sep 17 00:00:00 2001
From: Tarun Prabhu <tarun.prabhu at gmail.com>
Date: Wed, 22 Oct 2025 19:38:48 -0600
Subject: [PATCH 3/3] Fix clang-format error

---
 clang/lib/Driver/Driver.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index afaf6c2691ac6..71c52807091ba 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -317,9 +317,9 @@ InputArgList Driver::ParseArgStrings(ArrayRef<const char *> ArgStrings,
           DiagID = diag::err_drv_unknown_argument;
           Diags.Report(DiagID) << ArgString;
         }
-      } else if (!IsCLMode() &&
-          getOpts().findExact(ArgString, Nearest,
-                              llvm::opt::Visibility(options::CC1Option))) {
+      } else if (!IsCLMode() && getOpts().findExact(ArgString, Nearest,
+                                                    llvm::opt::Visibility(
+                                                        options::CC1Option))) {
         DiagID = diag::err_drv_unknown_argument_with_suggestion;
         Diags.Report(DiagID) << ArgString << "-Xclang " + Nearest;
       } else {