[Driver] Add disabled-by-default -Wuse-ld-path for the deprecation warning for -fuse-ld=/abs/path

[MaskRay]

Summary

The warning is currently not under a -W option, so it cannot be suppressed.
This is annoying for the widespread build system Bazel for specifying the path to gold
https://github.com/bazelbuild/bazel/commit/cdd0c3cdba270115940e8ca5ec8104cbcd694671

I have notified them about using --ld-path= forwards
https://github.com/bazelbuild/bazel/pull/8580#issuecomment-694321543
but we have to give some transitional period.

Intended for release/11.x for https://bugs.llvm.org/show_bug.cgi?id=47540

[chandlerc]

FWIW, I would like to see *something* like this (both in the release and on trunk) but not sure this is actually the patch we want... Clang typically uses FIXME comments, and doesn't leave commented out code...

I feel like this should be an off-by-default warning, with an actual warning flag maybe?

[MaskRay]

Add a warning flag

[dblaikie]

Rather than "non-word" maybe "path" would be more legible (that's the terminology the message text uses, and seems shorter/clearer in the warning name/constant name/etc), ie: -Wuse-ld-path

(how do other warnings about flags do naming regarding the 'f' (or 'g', etc) prefix - maybe "-Wfuse-ld-path" would be a more clear?)

[MaskRay]

Adopt dblaikie's suggestion: -Wfuse-ld-path

[chandlerc]

Good to confirm with Dave of course, but this looks pretty great to me, and thanks so much!

[dblaikie]

In D87837#2283784, @chandlerc wrote:

Good to confirm with Dave of course, but this looks pretty great to me, and thanks so much!

Works for me too!

clang/include/clang/Basic/DiagnosticDriverKinds.td

 def err_drv_unsupported_linker : Error<"unsupported value '%0' for -linker option">;
 def err_drv_defsym_invalid_format : Error<"defsym must be of the form: sym=value: %0">;
 def err_drv_defsym_invalid_symval : Error<"Value is not an integer: %0">;
 def warn_drv_msvc_not_found : Warning<
   "unable to find a Visual Studio installation; "
   "try running Clang from a developer command prompt">,
   InGroup<DiagGroup<"msvc-not-found">>;
 
-def warn_drv_use_ld_non_word : Warning<
-  "'-fuse-ld=' taking a path is deprecated. Use '--ld-path=' instead">;
+def warn_drv_fuse_ld_path : Warning<
+  "'-fuse-ld=' taking a path is deprecated. Use '--ld-path=' instead">,
+  InGroup<FUseLdPath>, DefaultIgnore;
 
 def warn_drv_fine_grained_bitfield_accesses_ignored : Warning<
   "option '-ffine-grained-bitfield-accesses' cannot be enabled together with a sanitizer; flag ignored">,
   InGroup<OptionIgnored>;
 
 def note_drv_verify_prefix_spelling : Note<
   "-verify prefixes must start with a letter and contain only alphanumeric"
   " characters, hyphens, and underscores">;

clang/include/clang/Basic/DiagnosticGroups.td

 def VoidPointerToEnumCast : DiagGroup<"void-pointer-to-enum-cast">;
 def VoidPointerToIntCast : DiagGroup<"void-pointer-to-int-cast",
                                      [VoidPointerToEnumCast]>;
 def PointerToEnumCast : DiagGroup<"pointer-to-enum-cast",
                                   [VoidPointerToEnumCast]>;
 def PointerToIntCast : DiagGroup<"pointer-to-int-cast",
                                  [PointerToEnumCast, VoidPointerToIntCast]>;
 
+def FUseLdPath : DiagGroup<"fuse-ld-path">;
+
 def Move : DiagGroup<"move", [
     PessimizingMove,
     RedundantMove,
     ReturnStdMove,
     SelfMove
   ]>;
 
 def Extra : DiagGroup<"extra", [
     DeprecatedCopy,
     MissingFieldInitializers,
     IgnoredQualifiers,
     InitializerOverrides,
     SemiBeforeMethodBody,
     MissingMethodReturnType,
     SignCompare,
     UnusedParameter,
     NullPointerArithmetic,
     EmptyInitStatement,
-    StringConcatation
+    StringConcatation,
+    FUseLdPath,
   ]>;
 
 def Most : DiagGroup<"most", [
     CharSubscript,
     Comment,
     DeleteNonVirtualDtor,
     Format,
     ForLoopAnalysis,

clang/lib/Driver/ToolChain.cpp

else
       return GetProgramPath(DefaultLinker);
   }
 
   // Extending -fuse-ld= to an absolute or relative path is unexpected. Checking
   // for the linker flavor is brittle. In addition, prepending "ld." or "ld64."
   // to a relative path is surprising. This is more complex due to priorities
   // among -B, COMPILER_PATH and PATH. --ld-path= should be used instead.
   if (UseLinker.find('/') != StringRef::npos)
-    getDriver().Diag(diag::warn_drv_use_ld_non_word);
+    getDriver().Diag(diag::warn_drv_fuse_ld_path);
 
   if (llvm::sys::path::is_absolute(UseLinker)) {
     // If we're passed what looks like an absolute path, don't attempt to
     // second-guess that.
     if (llvm::sys::fs::can_execute(UseLinker))
       return std::string(UseLinker);
   } else {
     llvm::SmallString<8> LinkerName;

clang/test/Driver/fuse-ld.c

-// RUN: %clang %s -### \
-// RUN:     -fuse-ld=/usr/local/bin/or1k-linux-ld 2>&1 \
-// RUN:     -target x86_64-unknown-linux \
-// RUN:   | FileCheck %s --check-prefix=CHECK-ABSOLUTE-LD
+/// The absolute path warning is enabled by -Wfuse-ld-path and -Wextra.
+// RUN: %clang %s -### -target x86_64-unknown-linux -Wfuse-ld-path \
+// RUN:   -fuse-ld=/usr/local/bin/or1k-linux-ld 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=CHECK-ABSOLUTE-LD
 // CHECK-ABSOLUTE-LD: warning: '-fuse-ld=' taking a path is deprecated. Use '--ld-path=' instead
 // CHECK-ABSOLUTE-LD: /usr/local/bin/or1k-linux-ld
 
+// RUN: %clang %s -### -target x86_64-unknown-linux -Wextra \
+// RUN:   -fuse-ld=/usr/local/bin/or1k-linux-ld 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=CHECK-ABSOLUTE-LD
+
+// RUN: %clang %s -### -target x86_64-unknown-linux \
+// RUN:   -fuse-ld=/usr/local/bin/or1k-linux-ld 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=CHECK-NO-WARN
+// CHECK-NO-WARN-NOT: warning:
 
 // RUN: %clang %s -### \
 // RUN:     -target x86_64-unknown-freebsd 2>&1 \
 // RUN:   | FileCheck %s --check-prefix=CHECK-FREEBSD-LD
 // CHECK-FREEBSD-LD: ld
 
 // RUN: %clang %s -### -fuse-ld=bfd \
 // RUN:     --sysroot=%S/Inputs/basic_freebsd_tree \

clang/test/Misc/warning-flags.c

(2) It prevents us adding new warnings to Clang that have no -W flag.  All
     new warnings should have -W flags.
 
     If you add a new warning without a flag, this test will fail.  To fix
     this test, simply add a warning group to that warning.
 
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (69):
+CHECK: Warnings without flags (68):
 
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_explicit_specialization_storage_class
 CHECK-NEXT:   ext_missing_declspec
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
 CHECK-NEXT:   ext_new_paren_array_nonconst
 CHECK-NEXT:   ext_plain_complex
 CHECK-NEXT:   ext_template_arg_extra_parens

 CHECK-NEXT:   warn_char_constant_too_large
 CHECK-NEXT:   warn_collection_expr_type
 CHECK-NEXT:   warn_conflicting_variadic
 CHECK-NEXT:   warn_delete_array_type
 CHECK-NEXT:   warn_double_const_requires_fp64
 CHECK-NEXT:   warn_drv_assuming_mfloat_abi_is
 CHECK-NEXT:   warn_drv_clang_unsupported
 CHECK-NEXT:   warn_drv_pch_not_first_include
-CHECK-NEXT:   warn_drv_use_ld_non_word
 CHECK-NEXT:   warn_dup_category_def
 CHECK-NEXT:   warn_enum_value_overflow
 CHECK-NEXT:   warn_expected_qualified_after_typename
 CHECK-NEXT:   warn_extraneous_char_constant
 CHECK-NEXT:   warn_fe_backend_unsupported
 CHECK-NEXT:   warn_fe_cc_log_diagnostics_failure
 CHECK-NEXT:   warn_fe_cc_print_header_failure
 CHECK-NEXT:   warn_fe_macro_contains_embedded_newline