add rustc setting use_default_shell_env

[oliverlee]

//rust/settings:use_default_shell_env is a bool flag that controls whether rustc actions inherit the shell environment. The default is False to maintain existing behavior.

This allows use in environments where PATH is set outside of Bazel's action environment, e.g. when using a Nix-based CcToolchain that relies on a Nix shell to populate PATH.

[oliverlee]

Related:
#2177
#3482
#3556
#3535

[UebelAndre]

Thanks! This seems like a reasonable compromise 😄

Just one question.

[UebelAndre]

Would it make more sense to have this on rust_toolchain?

[oliverlee]

I'm fine with either a toolchain flag or a global setting, although it seems unlikely a project would have multiple Rust toolchains where only some need the default shell env.

However, I don't have deep rules_rust experience, so feel free to disregard — at my day job I use Rust to build some tooling, though only ever with a single Rust toolchain.

[UebelAndre]

We currently have a big number of flags on the toolchain and feel it's much easier to manage having it there

rules_rust/rust/toolchain.bzl

Lines 637 to 651 in 71470d7

	# Experimental and incompatible flags
	_rename_first_party_crates = rename_first_party_crates,
	_third_party_dir = third_party_dir,
	_pipelined_compilation = pipelined_compilation,
	_experimental_link_std_dylib = _experimental_link_std_dylib(ctx),
	_experimental_use_cc_common_link = _experimental_use_cc_common_link(ctx),
	_experimental_use_global_allocator = experimental_use_global_allocator,
	_experimental_use_coverage_metadata_files = ctx.attr._experimental_use_coverage_metadata_files[BuildSettingInfo].value,
	_toolchain_generated_sysroot = ctx.attr._toolchain_generated_sysroot[BuildSettingInfo].value,
	_incompatible_do_not_include_data_in_compile_data = ctx.attr._incompatible_do_not_include_data_in_compile_data[IncompatibleFlagInfo].enabled,
	_incompatible_do_not_include_transitive_data_in_compile_inputs = ctx.attr._incompatible_do_not_include_transitive_data_in_compile_inputs[IncompatibleFlagInfo].enabled,
	_no_std = no_std,
	_codegen_units = ctx.attr._codegen_units[BuildSettingInfo].value,
	_experimental_use_allocator_libraries_with_mangled_symbols = ctx.attr.experimental_use_allocator_libraries_with_mangled_symbols,
	_experimental_use_allocator_libraries_with_mangled_symbols_setting = ctx.attr._experimental_use_allocator_libraries_with_mangled_symbols_setting[BuildSettingInfo].value,

Both work but if there's no string feelings or technical rationale (which I'm amenable to here) I'd prefer to have it on the toolchain

[oliverlee]

Sure I can take a look at it next week.