Auto merge of #114183 - Urgau:stabilize-print-with-path, r=oli-obk

Stabilize `PATH` option for `--print KIND=PATH`

This PR propose stabilizing the `PATH` option for `--print KIND=PATH`. This option was previously added in #113780 (as insta-stable before being un-stablized in #114139).

Description of the `PATH` option:
> A filepath may optionally be specified for each requested information kind, in the format `--print KIND=PATH`, just like for `--emit`. When a path is specified, information will be written there instead of to stdout.

------

Description of the original PR [\[link\]](#113780 (comment)):
> **Support --print KIND=PATH command line syntax**
>
> As is already done for `--emit KIND=PATH` and `-L KIND=PATH`.
>
> In the discussion of #110785, it was pointed out that `--print KIND=PATH` is nicer than trying to apply the single global `-o path` to `--print`'s output, because in general there can be multiple print requests within a single rustc invocation, and anyway `-o` would already be used for a different meaning in the case of `link-args` and `native-static-libs`.
>
> I am interested in using `--print cfg=PATH` in Buck2. Currently Buck2 works around the lack of support for `--print KIND=PATH` by [indirecting through a Python wrapper script](https://github.com/facebook/buck2/blob/d43cf3a51a31f00be2c2248e78271b0fef0452b4/prelude/rust/tools/get_rustc_cfg.py) to redirect rustc's stdout into the location dictated by the build system.
>
> From skimming Cargo's usages of `--print`, it definitely seems like it would benefit from `--print KIND=PATH` too. Currently it is working around the lack of this by inserting `--crate-name=___ --print=crate-name` so that it can look for a line containing `___` as a delimiter between the 2 other `--print` informations it actually cares about. This is commented as a "HACK" and "abuse". https://github.com/rust-lang/cargo/blob/31eda6f7c360d9911f853b3014e057db61238f3e/src/cargo/core/compiler/build_context/target_info.rs#L242

-----

cc `@dtolnay`
r? `@jackh726`

compiler/rustc_session/src/config.rs

@@ -2160,12 +2160,6 @@ fn collect_print_requests(
     prints.extend(matches.opt_strs("print").into_iter().map(|req| {
         let (req, out) = split_out_file_name(&req);
 
-        if out.is_some() && !unstable_opts.unstable_options {
-            handler.early_error(
-                "the `-Z unstable-options` flag must also be passed to \
-                 enable the path print option",
-            );
-        }
         let kind = match PRINT_KINDS.iter().find(|&&(name, _)| name == req) {
             Some((_, PrintKind::TargetSpec)) => {
                 if unstable_opts.unstable_options {

src/doc/rustc/src/command-line-arguments.md

@@ -260,6 +260,10 @@ The valid types of print values are:
   This returns rustc's minimum supported deployment target if no `*_DEPLOYMENT_TARGET` variable
   is present in the environment, or otherwise returns the variable's parsed value.
 
+A filepath may optionally be specified for each requested information kind, in
+the format `--print KIND=PATH`, just like for `--emit`. When a path is
+specified, information will be written there instead of to stdout.
+
 [conditional compilation]: ../reference/conditional-compilation.html
 [deployment target]: https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/cross_development/Configuring/configuring.html
 

tests/run-make/print-cfg/Makefile

@@ -13,19 +13,19 @@ all: default output_to_file
 
 output_to_file:
 	# Backend-independent, printed by rustc_driver_impl/src/lib.rs
-	$(RUSTC) --target x86_64-pc-windows-gnu --print cfg=$(TMPDIR)/cfg.txt -Z unstable-options
+	$(RUSTC) --target x86_64-pc-windows-gnu --print cfg=$(TMPDIR)/cfg.txt
 	$(CGREP) windows < $(TMPDIR)/cfg.txt
 
 	# Printed from CodegenBackend trait impl in rustc_codegen_llvm/src/lib.rs
-	$(RUSTC) --print relocation-models=$(TMPDIR)/relocation-models.txt -Z unstable-options
+	$(RUSTC) --print relocation-models=$(TMPDIR)/relocation-models.txt
 	$(CGREP) dynamic-no-pic < $(TMPDIR)/relocation-models.txt
 
 	# Printed by compiler/rustc_codegen_llvm/src/llvm_util.rs
-	$(RUSTC) --target wasm32-unknown-unknown --print target-features=$(TMPDIR)/target-features.txt -Z unstable-options
+	$(RUSTC) --target wasm32-unknown-unknown --print target-features=$(TMPDIR)/target-features.txt
 	$(CGREP) reference-types < $(TMPDIR)/target-features.txt
 
 	# Printed by C++ code in rustc_llvm/llvm-wrapper/PassWrapper.cpp
-	$(RUSTC) --target wasm32-unknown-unknown --print target-cpus=$(TMPDIR)/target-cpus.txt -Z unstable-options
+	$(RUSTC) --target wasm32-unknown-unknown --print target-cpus=$(TMPDIR)/target-cpus.txt
 	$(CGREP) generic < $(TMPDIR)/target-cpus.txt
 
 ifdef IS_WINDOWS