add shell completion for flamegraph

[ede1998]

About

This PR adds shell auto-completion support for the flamegraph binary. flamegraph --completions <shell> prints the completion script for the given shell to stdout. Currently supported shells are bash, fish, powershell andelvish (and zsh but it does not work).

Internally, claps completion generation is used.

Known issues/limitations:

Completions must be installed manually.

cargo install does not support installing extra files right now if claps documentation is to be believed. This means we cannot place a completion script into a completion directory for the user on install and would have to provide a distribution package (deb, rpm, ...) for this.

No completions for cargo flamegraph.

As far as I know, there is no official way to get completions for custom cargo subcommands. I tried getting it to work anyway without success. The issue is that you have to provide a binary name for which the completions will be generated. cargo-flamegraph sort of works for this if you invoke it directly but does not work at all when using cargo flamegraph as a custom subcommand. cargo as the binary name seems to be working great for cargo flamegraph. However it overrides existing completions so that you lose completions for cargo build etc.

Invoking flamegraph --completions zsh panics.

I didn't look into this. clap panics:

thread 'main' panicked at 'Fatal internal error. Please consider filing a bug report at https://github.com/clap-rs/clap/issues', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/completions/zsh.rs:346:29
stack backtrace:
   0: rust_begin_unwind
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/std/src/panicking.rs:515:5
   1: core::panicking::panic_fmt
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/panicking.rs:92:14
   2: core::option::expect_failed
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/option.rs:1243:5
   3: core::option::Option<T>::expect
             at /rustc/a178d0322ce20e33eac124758e837cbd80a6f633/library/core/src/option.rs:351:21
   4: clap::completions::zsh::write_opts_of
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/completions/zsh.rs:346:29
   5: clap::completions::zsh::get_args_of
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/completions/zsh.rs:284:16
   6: clap::completions::zsh::ZshGen::generate_to
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/completions/zsh.rs:56:32
   7: clap::completions::ComplGen::generate
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/completions/mod.rs:38:27
   8: clap::app::parser::Parser::gen_completions_to
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/app/parser.rs:121:9
   9: clap::app::App::gen_completions_to
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/clap-2.33.3/src/app/mod.rs:1442:9
  10: flamegraph::main

[djc]

Thanks for working on this!

[djc]

I added some conflict handling in f5a1b9c. Doesn't need to be with all the options, just the ones that allow specifying a workload.