Auto merge of #98843 - Urgau:check-cfg-stage0, r=Mark-Simulacrum

Enable check-cfg in stage0

Now that the bootstrap cargo supports `rustc-check-cfg` we can now enable it with `-Zcheck-cfg=output` and use it in `rustc_llvm` to unblock `--check-cfg` support in stage0.

r? `@Mark-Simulacrum`

compiler/rustc_llvm/build.rs

@@ -4,6 +4,29 @@ use std::fmt::Display;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
 
+const OPTIONAL_COMPONENTS: &[&str] = &[
+    "x86",
+    "arm",
+    "aarch64",
+    "amdgpu",
+    "avr",
+    "m68k",
+    "mips",
+    "powerpc",
+    "systemz",
+    "jsbackend",
+    "webassembly",
+    "msp430",
+    "sparc",
+    "nvptx",
+    "hexagon",
+    "riscv",
+    "bpf",
+];
+
+const REQUIRED_COMPONENTS: &[&str] =
+    &["ipo", "bitreader", "bitwriter", "linker", "asmparser", "lto", "coverage", "instrumentation"];
+
 fn detect_llvm_link() -> (&'static str, &'static str) {
     // Force the link mode we want, preferring static by default, but
     // possibly overridden by `configure --enable-llvm-link-shared`.
@@ -76,6 +99,10 @@ fn output(cmd: &mut Command) -> String {
 }
 
 fn main() {
+    for component in REQUIRED_COMPONENTS.iter().chain(OPTIONAL_COMPONENTS.iter()) {
+        println!("cargo:rustc-check-cfg=values(llvm_component,\"{}\")", component);
+    }
+
     if tracked_env_var_os("RUST_CHECK").is_some() {
         // If we're just running `check`, there's no need for LLVM to be built.
         return;
@@ -131,42 +158,11 @@ fn main() {
     let host = env::var("HOST").expect("HOST was not set");
     let is_crossed = target != host;
 
-    let optional_components = &[
-        "x86",
-        "arm",
-        "aarch64",
-        "amdgpu",
-        "avr",
-        "m68k",
-        "mips",
-        "powerpc",
-        "systemz",
-        "jsbackend",
-        "webassembly",
-        "msp430",
-        "sparc",
-        "nvptx",
-        "hexagon",
-        "riscv",
-        "bpf",
-    ];
-
-    let required_components = &[
-        "ipo",
-        "bitreader",
-        "bitwriter",
-        "linker",
-        "asmparser",
-        "lto",
-        "coverage",
-        "instrumentation",
-    ];
-
     let components = output(Command::new(&llvm_config).arg("--components"));
     let mut components = components.split_whitespace().collect::<Vec<_>>();
-    components.retain(|c| optional_components.contains(c) || required_components.contains(c));
+    components.retain(|c| OPTIONAL_COMPONENTS.contains(c) || REQUIRED_COMPONENTS.contains(c));
 
-    for component in required_components {
+    for component in REQUIRED_COMPONENTS {
         if !components.contains(component) {
             panic!("require llvm component {} but wasn't found", component);
         }

src/bootstrap/builder.rs

@@ -1468,11 +1468,6 @@ impl<'a> Builder<'a> {
             rustflags.arg("-Zunstable-options");
         }
 
-        // FIXME(Urgau): This a hack as it shouldn't be gated on stage 0 but until `rustc_llvm`
-        // is made to work with `--check-cfg` which is currently not easly possible until cargo
-        // get some support for setting `--check-cfg` within build script, it's the least invasive
-        // hack that still let's us have cfg checking for the vast majority of the codebase.
-        if stage != 0 {
         // Enable cfg checking of cargo features for everything but std and also enable cfg
         // checking of names and values.
         //
@@ -1482,9 +1477,9 @@ impl<'a> Builder<'a> {
         // complete list of features, so for that reason we don't enable checking of
         // features for std crates.
         cargo.arg(if mode != Mode::Std {
-                "-Zcheck-cfg=names,values,features"
+            "-Zcheck-cfg=names,values,output,features"
         } else {
-                "-Zcheck-cfg=names,values"
+            "-Zcheck-cfg=names,values,output"
         });
 
         // Add extra cfg not defined in/by rustc
@@ -1508,7 +1503,6 @@ impl<'a> Builder<'a> {
                 rustflags.arg(&format!("--check-cfg=values({name}{values})"));
             }
         }
-        }
 
         // FIXME: It might be better to use the same value for both `RUSTFLAGS` and `RUSTDOCFLAGS`,
         // but this breaks CI. At the very least, stage0 `rustdoc` needs `--cfg bootstrap`. See