Flag also parsed as positional argument

[Mark-Simulacrum]

Rust Version

N/A, but tested on latest nightly

Affected Version of clap

2.22.1

Expected Behavior Summary

With a single, optional positional argument and a flag, we don't parse the flag as the positional argument. I also set AllowLeadingHyphen, since some of my arguments start with -C.

Actual Behavior Summary

The optional positional argument is parsed as Some("--verbose") instead of None, and --verbose is also parsed.

Steps to Reproduce the issue

I'm not really sure what to put here, but basically

app --verbose is parsed as:

• is_present("--verbose") = true
• `value_of("filter") == Some("--verbose")

Sample Code or Link to Sample Code

https://github.com/Mark-Simulacrum/rust/tree/cleanup is the branch, but you'll need to cd to src/tools/compiletest and then just cargo build should work.

After that, running this command reproduces the issue, pay attention to how filter is printed as Some("--verbose") in the debug output:

./src/target/debug/compiletest "--compile-lib-path" "./rust/build/x86_64-unknown-linux-gnu/stage1/lib" "--run-lib-path" "./rust/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "./rust/build/x86_64-unknown-linux-gnu/stage1/bin/rustc" "--rustdoc-path" "./rust/build/x86_64-unknown-linux-gnu/stage1/bin/rustdoc" "--src-base" "./rust/src/test/compile-fail" "--build-base" "./rust/build/x86_64-unknown-linux-gnu/test/compile-fail" "--stage-id" "stage1-x86_64-unknown-linux-gnu" "--mode" "compile-fail" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "./rust/build/x86_64-unknown-linux-gnu/llvm/build/bin/FileCheck" "--nodejs" "/usr/bin/node" "--host-rustcflags" "-Crpath -O" "--target-rustcflags" "-Crpath -O -Lnative=./rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--llvm-version" "4.0.1\n" "--verbose" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" ""

Debug output

https://gist.github.com/Mark-Simulacrum/b86c4f16f922be7ef542e7853cf93e01, with what I think being relevant here: https://gist.github.com/Mark-Simulacrum/b86c4f16f922be7ef542e7853cf93e01#file-gistfile1-txt-L1590

[kbknapp]

Thanks for taking the time to file this! I've confirmed the bug, and it should be an easy one to fix.

Also, just to note AllowLeadingHyphen is for when values may start with a hyphen, and should be used sparingly if possible. A better option is to use allow_hyphen_values only on the args who's values may start with a leading hyphen. It's not critical, I just wanted to note it (and if you already knew this I apologize 😄)

[Mark-Simulacrum]

Great! Thanks for pointing out that there's a difference between AllowLeadingHypen and allow_hyphen_values, but I think I'm confused (feel free to tell me I should move this to another issue). The documentation for AllowLeadingHyphen suggests that I have to set that globally: "NOTE: This can only be set application wide and not on a per argument basis." But what you're saying seems to suggest that's not the case?

[kbknapp]

there's a difference between AllowLeadingHypen and allow_hyphen_values, but I think I'm confused

They do the same thing, one is globally (AllowLeadingHyphen) and the other is per argument (allow_hyphen_values).

The documentation is out of date (embarrassed). That was true before allow_hyphen_values was introduced. I'm updating it as we speak.

[kbknapp]

2.24.1 is on crates.io