x.py should not die if I set `RUSTFLAGS=--color=never` in the env

[pnkfelix]

Right, now, if I do RUSTFLAGS=--color=never x.py build, I get:

Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
error: failed to run `rustc` to learn about target-specific information

Caused by:
  process didn't exit successfully: `/home/pnkfelix/Dev/Mozilla/issue27282/rust-27282/objdir-dbgopt/build/bootstrap/debug/rustc - --crate-name ___ --print=file-names --color=never --target x86_64-unknown-linux-gnu --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro` (exit code: 101)
--- stderr
error: Option 'color' given more than once

My initial inference here is that we are dying because rustc is getting multiple --color=never directives (and one is coming in implicitly via RUSTFLAGS

In my opinion, rustc should allow one to pass --color=never multiple times. (Arguably other combinations of --color should also be allowed.)

• Perhaps we should go even further and determine general precedence rules for mixing RUSTFLAGS input with command line input. But I digress.

But if we want to continue having rustc be strict about that, then x.py needs to be smarter about looking at the environment when it decides what arguments to pass to the rustc it invokes.

[Mark-Simulacrum]

This is also presumably and probably the case for a variety of other options that we currently pass to rustc in rustbuild; I agree that this feels like a rustc bug, but it should be somewhat easy to fix or patch over in rustbuild if we wanted to...

[jyn514]

bootstrap now has built-in support for --color (since #79004) and RUSTFLAGS=--color fails for other reasons that are cargo related and not controlled by bootstrap:

error: cannot specify the `--color` option with `--json`

I'm going to close this since this specific issue is no longer relevant; if you think rustc should accept multiple flags that do the same thing I agree :) but I think that deserves an MCP rather than sitting in the issue tracker ignored.