From 39e619c3753e6fd182719733c76d9dc04ea9b622 Mon Sep 17 00:00:00 2001
From: Pavel Grigorenko <GrigorenkoPV@ya.ru>
Date: Fri, 27 Jun 2025 01:44:28 +0300
Subject: [PATCH] bootstrap: `validate rust.codegen-backends` &
 `targer.<triple>.codegen-backends`

---
 src/bootstrap/src/core/config/toml/rust.rs   | 43 ++++++++++++--------
 src/bootstrap/src/core/config/toml/target.rs | 22 ++--------
 2 files changed, 29 insertions(+), 36 deletions(-)

diff --git a/src/bootstrap/src/core/config/toml/rust.rs b/src/bootstrap/src/core/config/toml/rust.rs
index 642f2f2271d8f..6b33d06c67d98 100644
--- a/src/bootstrap/src/core/config/toml/rust.rs
+++ b/src/bootstrap/src/core/config/toml/rust.rs
@@ -393,6 +393,27 @@ pub fn check_incompatible_options_for_ci_rustc(
     Ok(())
 }
 
+pub(crate) const VALID_CODEGEN_BACKENDS: &[&str] = &["llvm", "cranelift", "gcc"];
+
+pub(crate) fn validate_codegen_backends(backends: Vec<String>, section: &str) -> Vec<String> {
+    for backend in &backends {
+        if let Some(stripped) = backend.strip_prefix(CODEGEN_BACKEND_PREFIX) {
+            panic!(
+                "Invald value '{backend}' for '{section}.codegen-backends'. \
+                Codegen backends are defined without the '{CODEGEN_BACKEND_PREFIX}' prefix. \
+                Please, use '{stripped}' instead."
+            )
+        }
+        if !VALID_CODEGEN_BACKENDS.contains(&&**backend) {
+            println!(
+                "HELP: '{backend}' for '{section}.codegen-backends' might fail. \
+                List of known good values: {VALID_CODEGEN_BACKENDS:?}"
+            );
+        }
+    }
+    backends
+}
+
 impl Config {
     pub fn apply_rust_config(
         &mut self,
@@ -571,24 +592,10 @@ impl Config {
             set(&mut self.ehcont_guard, ehcont_guard);
             self.llvm_libunwind_default =
                 llvm_libunwind.map(|v| v.parse().expect("failed to parse rust.llvm-libunwind"));
-
-            if let Some(ref backends) = codegen_backends {
-                let available_backends = ["llvm", "cranelift", "gcc"];
-
-                self.rust_codegen_backends = backends.iter().map(|s| {
-                    if let Some(backend) = s.strip_prefix(CODEGEN_BACKEND_PREFIX) {
-                        if available_backends.contains(&backend) {
-                            panic!("Invalid value '{s}' for 'rust.codegen-backends'. Instead, please use '{backend}'.");
-                        } else {
-                            println!("HELP: '{s}' for 'rust.codegen-backends' might fail. \
-                                Codegen backends are mostly defined without the '{CODEGEN_BACKEND_PREFIX}' prefix. \
-                                In this case, it would be referred to as '{backend}'.");
-                        }
-                    }
-
-                    s.clone()
-                }).collect();
-            }
+            set(
+                &mut self.rust_codegen_backends,
+                codegen_backends.map(|backends| validate_codegen_backends(backends, "rust")),
+            );
 
             self.rust_codegen_units = codegen_units.map(threads_from_config);
             self.rust_codegen_units_std = codegen_units_std.map(threads_from_config);
diff --git a/src/bootstrap/src/core/config/toml/target.rs b/src/bootstrap/src/core/config/toml/target.rs
index b9f6780ca3fe1..337276948b324 100644
--- a/src/bootstrap/src/core/config/toml/target.rs
+++ b/src/bootstrap/src/core/config/toml/target.rs
@@ -16,7 +16,7 @@ use std::collections::HashMap;
 
 use serde::{Deserialize, Deserializer};
 
-use crate::core::build_steps::compile::CODEGEN_BACKEND_PREFIX;
+use crate::core::config::toml::rust::validate_codegen_backends;
 use crate::core::config::{LlvmLibunwind, Merge, ReplaceOpt, SplitDebuginfo, StringOrBool};
 use crate::{Config, HashSet, PathBuf, TargetSelection, define_config, exit};
 
@@ -142,23 +142,9 @@ impl Config {
                 target.rpath = cfg.rpath;
                 target.optimized_compiler_builtins = cfg.optimized_compiler_builtins;
                 target.jemalloc = cfg.jemalloc;
-
-                if let Some(ref backends) = cfg.codegen_backends {
-                    let available_backends = ["llvm", "cranelift", "gcc"];
-
-                    target.codegen_backends = Some(backends.iter().map(|s| {
-                        if let Some(backend) = s.strip_prefix(CODEGEN_BACKEND_PREFIX) {
-                            if available_backends.contains(&backend) {
-                                panic!("Invalid value '{s}' for 'target.{triple}.codegen-backends'. Instead, please use '{backend}'.");
-                            } else {
-                                println!("HELP: '{s}' for 'target.{triple}.codegen-backends' might fail. \
-                                    Codegen backends are mostly defined without the '{CODEGEN_BACKEND_PREFIX}' prefix. \
-                                    In this case, it would be referred to as '{backend}'.");
-                            }
-                        }
-
-                        s.clone()
-                    }).collect());
+                if let Some(backends) = cfg.codegen_backends {
+                    target.codegen_backends =
+                        Some(validate_codegen_backends(backends, &format!("target.{triple}")))
                 }
 
                 target.split_debuginfo = cfg.split_debuginfo.as_ref().map(|v| {