Unusual behavior when using "-" or "--" and using or omitting equal signs in the command line

[Yewzir]

I happened to see something about the "--target" command-line flag in the Clang compiler. Previously, I wanted to run a command that would generate code for a specific target during compilation, but that didn't go smoothly and led me here.

Below are four uses of the flag, half of which fail. Pay particular attention to the use of the number of dashes and the equal signs.

$ clang --target=x86_64-unknown-linux-gnu hello.c
$ ./a.out
Hello, World

$ clang --target x86_64-unknown-linux-gnu hello.c
clang: error: unknown argument '--target'; did you mean '-target'?
clang: error: no such file or directory: 'x86_64-unknown-linux-gnu'

$ clang -target x86_64-unknown-linux-gnu hello.c
$ ./a.out
Hello, World

$ clang -target=x86_64-unknown-linux-gnu hello.c
clang: error: unknown argument '-target=x86_64-unknown-linux-gnu'; did you mean '--target=x86_64-unknown-linux-gnu'?

It's striking how the second example suggests using "-target", when the way I used the flag is exactly the documented way, at least as far as the double hyphens are concerned. I also find it striking that "--target" works with an equals sign, but not without, while "-target" works the other way around, because it doesn't work with the equals sign, but does work without it.

For example, the "--config" flag is documented in the same way, but works with and without the equals sign.

I definitely wanted to share this because I'm not sure if this is intentional.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: Hicham Omari (Yewzir)

I happened to see something about the "--target" command-line flag in the Clang compiler. Previously, I wanted to run a command that would generate code for a specific target during compilation, but that didn't go smoothly and led me here.

Below are four uses of the flag, half of which fail. Pay particular attention to the use of the number of dashes and the equal signs.

$ clang --target=x86_64-unknown-linux-gnu hello.c
$ ./a.out
Hello, World

$ clang --target x86_64-unknown-linux-gnu hello.c
clang: error: unknown argument '--target'; did you mean '-target'?
clang: error: no such file or directory: 'x86_64-unknown-linux-gnu'

$ clang -target x86_64-unknown-linux-gnu hello.c
$ ./a.out
Hello, World

$ clang -target=x86_64-unknown-linux-gnu hello.c
clang: error: unknown argument '-target=x86_64-unknown-linux-gnu'; did you mean '--target=x86_64-unknown-linux-gnu'?

It's striking how the second example suggests using "-target", when the way I used the flag is exactly the documented way, at least as far as the double hyphens are concerned. I also find it striking that "--target" works with an equals sign, but not without, while "-target" works the other way around, because it doesn't work with the equals sign, but does work without it.

For example, the "--config" flag is documented in the same way, but works with and without the equals sign.

I definitely wanted to share this because I'm not sure if this is intentional.

[Xen00n]

I reproduced the inconsistent behavior of the -target/--target flags on macOS (Apple Clang 17).

Commands and results:

1. clang --target=arm64-apple-darwin test.c
   Works

2. clang --target arm64-apple-darwin test.c
   Fails :

clang: error: unknown argument '--target'; did you mean '-target'?
clang: error: no such file or directory: 'arm64-apple-darwin'

3. clang -target arm64-apple-darwin test.c
   Works

4. clang -target=arm64-apple-darwin test.c
   Fails :
   clang: error: unknown argument '-target=arm64-apple-darwin'; did you mean '--target=arm64-apple-darwin'?

[zhaoqi5]

This is the behavior expected by clang driver at present. As shown blow:

• This allows --target=xxx:
  

  llvm-project/clang/include/clang/Driver/Options.td

  Lines 6201 to 6203 in 6ac40aa

  	def target : Joined<["--"], "target=">, Flags<[NoXarchOption]>,
  	Visibility<[ClangOption, CLOption, DXCOption, FlangOption]>,
  	HelpText<"Generate code for the given target">;

• This allows -target xxx, and seems to be a legacy usage:
  

  llvm-project/clang/include/clang/Driver/Options.td

  Lines 6878 to 6883 in 6ac40aa

  	// These are legacy user-facing driver-level option spellings. They are always
  	// aliases for options that are spelled using the more common Unix / GNU flag
  	// style of double-dash and equals-joined flags.
  	def target_legacy_spelling : Separate<["-"], "target">,
  	Alias<target>,
  	Visibility<[ClangOption, CLOption, DXCOption, FlangOption]>;

Any other usage is not allowed.