[clang] [Driver] Add an option to disable default config filenames

[mgorny]

Summary

Add a --no-default-config option that disables the search for default
set of config filenames (based on the compiler executable name).

Suggested in https://discourse.llvm.org/t/rfc-adding-a-default-file-location-to-config-file-support/63606.

[MaskRay]

This makes sense.

clang/lib/Driver/Driver.cpp

1027–1034

&& ?

clang/test/Driver/config-file3.c

53

The convention doesn't use otherwise empty // . The file does not obey the convention but your new lines can drop the empty //

[mgorny]

clang/lib/Driver/Driver.cpp

1027–1034

&& would mean dereferencing null pointer ;-).

clang/test/Driver/config-file3.c

53

Do you mean the extra space or the entire empty line?

[MaskRay]

LGTM.

clang/lib/Driver/Driver.cpp

1027–1034

oh, i misread. sorry. the two if can be merged

clang/test/Driver/config-file3.c

53

I mean ^// *$, which typically makes the test harder to browse.

(Think of { } in vim. If every line has //, { } isn't effective at all.)

[mgorny]

Replace !x || !y logic with !(x && y) that may be easier to comprehend.

Replace // with empty lines on test boundaries.

[mgorny]

clang/lib/Driver/Driver.cpp

1027–1034

I've deliberately left it like that to account for possibly more rules being added in the future (e.g. explicit -target, given the discourse discussion).

I've changed !x || !y to !(x && y), perhaps that will be less confusing.

clang/test/Driver/config-file3.c

53

Oh, so you mean to have empty lines between tests to make it easier to navigate between tests? Please let me know if I got this right.

[MaskRay]

clang/test/Driver/config-file3.c

44

Append . after a complete sentence in a comment.

53

Thanks, this looks better. I think the convention is not to even leave ^//$ between RUN and CHECK, but the current form is already good enough.

[mgorny]

Thanks! I'm going to give others a few more hours to chime in before merging it.

[sepavloff]

LGTM.

Thanks!

clang/docs/UsersManual.rst

treated as a file name and is searched for sequentially in the directories:
     - system directory,
     - the directory where Clang executable resides.
 
 Both user and system directories for configuration files are specified during
 clang build using CMake parameters, CLANG_CONFIG_FILE_USER_DIR and
 CLANG_CONFIG_FILE_SYSTEM_DIR respectively. The first file found is used. It is
 an error if the required file cannot be found.
 
+If no explicit configuration file is specified, Clang searches for a default
+configuration file following the rules described in the next paragraphs.
+To disable this behavior, `--no-default-config` flag can be used.
+
 Another way to specify a configuration file is to encode it in executable name.
 For example, if the Clang executable is named `armv7l-clang` (it may be a
 symbolic link to `clang`), then Clang will search for file `armv7l.cfg` in the
 directory where Clang resides.
 
 If a driver mode is specified in invocation, Clang tries to find a file specific
 for the specified mode. For example, if the executable file is named
 `x86_64-clang-cl`, Clang first looks for `x86_64-cl.cfg` and if it is not found,

clang/include/clang/Driver/Options.td

HelpText<"OpenCL only. Enable or disable OpenCL extensions/optional features. The argument is a comma-separated "
            "sequence of one or more extension names, each prefixed by '+' or '-'.">,
   MarshallingInfoStringVector<TargetOpts<"OpenCLExtensionsAsWritten">>;
 
 def client__name : JoinedOrSeparate<["-"], "client_name">;
 def combine : Flag<["-", "--"], "combine">, Flags<[NoXarchOption, Unsupported]>;
 def compatibility__version : JoinedOrSeparate<["-"], "compatibility_version">;
 def config : Separate<["--"], "config">, Flags<[NoXarchOption]>,
   HelpText<"Specifies configuration file">;
+def no_default_config : Flag<["--"], "no-default-config">, Flags<[NoXarchOption]>,
+  HelpText<"Disable loading default configuration files">;
 def config_system_dir_EQ : Joined<["--"], "config-system-dir=">, Flags<[NoXarchOption, HelpHidden]>,
   HelpText<"System directory for configuration files">;
 def config_user_dir_EQ : Joined<["--"], "config-user-dir=">, Flags<[NoXarchOption, HelpHidden]>,
   HelpText<"User directory for configuration files">;
 def coverage : Flag<["-", "--"], "coverage">, Group<Link_Group>, Flags<[CoreOption]>;
 def cpp_precomp : Flag<["-"], "cpp-precomp">, Group<clang_ignored_f_Group>;
 def current__version : JoinedOrSeparate<["-"], "current_version">;
 def cxx_isystem : JoinedOrSeparate<["-"], "cxx-isystem">, Group<clang_i_Group>,

clang/lib/Driver/Driver.cpp

if (!ConfigFiles.empty()) {
         }
         return readConfigFile(CfgFilePath);
       }
 
       FileSpecifiedExplicitly = true;
     }
   }
 
+  if (!(CLOptions && CLOptions->hasArg(options::OPT_no_default_config))) {
     // If config file is not specified explicitly, try to deduce configuration
     // from executable name. For instance, an executable 'armv7l-clang' will
     // search for config file 'armv7l-clang.cfg'.
     if (CfgFileName.empty() && !ClangNameParts.TargetPrefix.empty())
-    CfgFileName = ClangNameParts.TargetPrefix + '-' + ClangNameParts.ModeSuffix;
+      CfgFileName =
+          ClangNameParts.TargetPrefix + '-' + ClangNameParts.ModeSuffix;
+  }
 
   if (CfgFileName.empty())
     return false;
 
   // Determine architecture part of the file name, if it is present.
   StringRef CfgFileArch = CfgFileName;
   size_t ArchPrefixLen = CfgFileArch.find('-');
   if (ArchPrefixLen == StringRef::npos)

clang/test/Driver/config-file3.c

 //
 // SYMLINK: Configuration file: {{.*}}/testdmode/qqq-clang-g++.cfg
 //
 //--- File specified by --config overrides config inferred from clang executable.
 //
 // RUN: %t/testdmode/qqq-clang-g++ --config-system-dir=%S/Inputs/config --config-user-dir= --config i386-qqq -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix CHECK-EXPLICIT
 //
 // CHECK-EXPLICIT: Configuration file: {{.*}}/Inputs/config/i386-qqq.cfg
+
+//--- --no-default-config disables config search.
+//
+// RUN: %t/testdmode/qqq-clang-g++ --config-system-dir= --config-user-dir=%t/testdmode --no-default-config -c -### %s 2>&1 | FileCheck %s -check-prefix NO-DEFAULT-CONFIG
 //
+// NO-DEFAULT-CONFIG-NOT: Configuration file:
+
 //--- Invocation qqq-clang-g++ tries to find config file qqq.cfg if qqq-clang-g++.cfg is not found.
 //
 // RUN: rm %t/testdmode/qqq-clang-g++.cfg
 // RUN: %t/testdmode/qqq-clang-g++ --config-system-dir= --config-user-dir= -c -no-canonical-prefixes -### %s 2>&1 | FileCheck %s -check-prefix SHORT-NAME
 //
 // SHORT-NAME: Configuration file: {{.*}}/testdmode/qqq.cfg
 // SHORT-NAME: -Werror
 // SHORT-NAME-NOT: -Wundefined-func-template
 
 
 //--- Config files are searched for in binary directory as well.
 //