add test coverage for RUSTC_IF_UNCHANGED_ALLOWED_PATHS

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/core/config/config.rs

@@ -37,7 +37,7 @@ use crate::utils::helpers::{self, exe, output, t};
 ///
 /// WARNING: Be cautious when adding paths to this list. If a path that influences the compiler build
 /// is added here, it will cause bootstrap to skip necessary rebuilds, which may lead to risky results.
-const RUSTC_IF_UNCHANGED_ALLOWED_PATHS: &[&str] = &[
+pub(crate) const RUSTC_IF_UNCHANGED_ALLOWED_PATHS: &[&str] = &[
     ":!.clang-format",
     ":!.editorconfig",
     ":!.git-blame-ignore-revs",

src/bootstrap/src/core/config/tests.rs

@@ -8,7 +8,7 @@ use clap::CommandFactory;
 use serde::Deserialize;
 
 use super::flags::Flags;
-use super::{ChangeIdWrapper, Config};
+use super::{ChangeIdWrapper, Config, RUSTC_IF_UNCHANGED_ALLOWED_PATHS};
 use crate::core::build_steps::clippy::get_clippy_rules_in_order;
 use crate::core::build_steps::llvm;
 use crate::core::config::{LldMode, Target, TargetSelection, TomlConfig};
@@ -410,3 +410,18 @@ fn jobs_precedence() {
     );
     assert_eq!(config.jobs, Some(123));
 }
+
+#[test]
+fn check_rustc_if_unchanged_paths() {
+    let config = parse("");
+    let normalised_allowed_paths: Vec<_> = RUSTC_IF_UNCHANGED_ALLOWED_PATHS
+        .iter()
+        .map(|t| {
+            t.strip_prefix(":!").expect(&format!("{t} doesn't have ':!' prefix, but it should."))
+        })
+        .collect();
+
+    for p in normalised_allowed_paths {
+        assert!(config.src.join(p).exists(), "{p} doesn't exist.");
+    }
+}