Unify LLVM invalidation path handling

Before it was using a different set of paths in different call-sites.

Author: Kobzol

Diff for: src/bootstrap/src/core/build_steps/gcc.rs

@@ -273,7 +273,7 @@ fn detect_gcc_sha(config: &crate::Config, is_git: bool) -> String {
         get_closest_merge_commit(
             Some(&config.src),
             &config.git_config(),
-            &[config.src.join("src/gcc"), config.src.join("src/bootstrap/download-ci-gcc-stamp")],
+            &["src/gcc", "src/bootstrap/download-ci-gcc-stamp"],
         )
         .unwrap()
     } else if let Some(info) = crate::utils::channel::read_commit_info_file(&config.src) {

Diff for: src/bootstrap/src/core/build_steps/llvm.rs

@@ -174,20 +174,19 @@ pub fn prebuilt_llvm_config(
     LlvmBuildStatus::ShouldBuild(Meta { stamp, res, out_dir, root: root.into() })
 }
 
+/// Paths whose changes invalidate LLVM downloads.
+pub const LLVM_INVALIDATION_PATHS: &[&str] = &[
+    "src/llvm-project",
+    "src/bootstrap/download-ci-llvm-stamp",
+    // the LLVM shared object file is named `LLVM-<LLVM-version>-rust-{version}-nightly`
+    "src/version",
+];
+
 /// This retrieves the LLVM sha we *want* to use, according to git history.
 pub(crate) fn detect_llvm_sha(config: &Config, is_git: bool) -> String {
     let llvm_sha = if is_git {
-        get_closest_merge_commit(
-            Some(&config.src),
-            &config.git_config(),
-            &[
-                config.src.join("src/llvm-project"),
-                config.src.join("src/bootstrap/download-ci-llvm-stamp"),
-                // the LLVM shared object file is named `LLVM-12-rust-{version}-nightly`
-                config.src.join("src/version"),
-            ],
-        )
-        .unwrap()
+        get_closest_merge_commit(Some(&config.src), &config.git_config(), LLVM_INVALIDATION_PATHS)
+            .unwrap()
     } else if let Some(info) = crate::utils::channel::read_commit_info_file(&config.src) {
         info.sha.trim().to_owned()
     } else {

Diff for: src/bootstrap/src/core/config/config.rs

@@ -23,6 +23,7 @@ use tracing::{instrument, span};
 
 use crate::core::build_steps::compile::CODEGEN_BACKEND_PREFIX;
 use crate::core::build_steps::llvm;
+use crate::core::build_steps::llvm::LLVM_INVALIDATION_PATHS;
 pub use crate::core::config::flags::Subcommand;
 use crate::core::config::flags::{Color, Flags, Warnings};
 use crate::core::download::is_download_ci_available;
@@ -3109,9 +3110,9 @@ impl Config {
             #[cfg(not(test))]
             self.update_submodule("src/llvm-project");
 
-            // Check for untracked changes in `src/llvm-project`.
+            // Check for untracked changes in `src/llvm-project` and other important places.
             let has_changes = self
-                .last_modified_commit(&["src/llvm-project"], "download-ci-llvm", true)
+                .last_modified_commit(LLVM_INVALIDATION_PATHS, "download-ci-llvm", true)
                 .is_none();
 
             // Return false if there are untracked changes, otherwise check if CI LLVM is available.

Diff for: src/bootstrap/src/core/config/tests.rs

@@ -12,6 +12,7 @@ use super::flags::Flags;
 use super::{ChangeIdWrapper, Config, RUSTC_IF_UNCHANGED_ALLOWED_PATHS};
 use crate::core::build_steps::clippy::{LintConfig, get_clippy_rules_in_order};
 use crate::core::build_steps::llvm;
+use crate::core::build_steps::llvm::LLVM_INVALIDATION_PATHS;
 use crate::core::config::{LldMode, Target, TargetSelection, TomlConfig};
 
 pub(crate) fn parse(config: &str) -> Config {
@@ -41,7 +42,7 @@ fn download_ci_llvm() {
     let if_unchanged_config = parse("llvm.download-ci-llvm = \"if-unchanged\"");
     if if_unchanged_config.llvm_from_ci {
         let has_changes = if_unchanged_config
-            .last_modified_commit(&["src/llvm-project"], "download-ci-llvm", true)
+            .last_modified_commit(LLVM_INVALIDATION_PATHS, "download-ci-llvm", true)
             .is_none();
 
         assert!(

Diff for: src/build_helper/src/git.rs

@@ -1,4 +1,4 @@
-use std::path::{Path, PathBuf};
+use std::path::Path;
 use std::process::{Command, Stdio};
 
 use crate::ci::CiEnv;
@@ -121,7 +121,7 @@ fn git_upstream_merge_base(
 pub fn get_closest_merge_commit(
     git_dir: Option<&Path>,
     config: &GitConfig<'_>,
-    target_paths: &[PathBuf],
+    target_paths: &[&str],
 ) -> Result<String, String> {
     let mut git = Command::new("git");