abstract merge-base commit logic

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

Author: onur-ozkan

src/bootstrap/src/core/build_steps/llvm.rs

@@ -20,13 +20,13 @@ use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
 use crate::core::config::{Config, TargetSelection};
 use crate::utils::channel;
 use crate::utils::helpers::{
-    self, exe, get_clang_cl_resource_dir, output, t, unhashed_basename, up_to_date,
+    self, exe, get_clang_cl_resource_dir, get_closest_merge_base_commit, output, t,
+    unhashed_basename, up_to_date,
 };
 use crate::{generate_smart_stamp_hash, CLang, GitRepo, Kind};
 
 use crate::utils::exec::command;
 use build_helper::ci::CiEnv;
-use build_helper::git::get_git_merge_base;
 
 #[derive(Clone)]
 pub struct LlvmResult {
@@ -153,26 +153,18 @@ pub fn prebuilt_llvm_config(builder: &Builder<'_>, target: TargetSelection) -> L
 /// 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 {
-        // We proceed in 2 steps. First we get the closest commit that is actually upstream. Then we
-        // walk back further to the last bors merge commit that actually changed LLVM. The first
-        // step will fail on CI because only the `auto` branch exists; we just fall back to `HEAD`
-        // in that case.
-        let closest_upstream = get_git_merge_base(&config.git_config(), Some(&config.src))
-            .unwrap_or_else(|_| "HEAD".into());
-        let mut rev_list = helpers::git(Some(&config.src));
-        rev_list.args(&[
-            PathBuf::from("rev-list"),
-            format!("--author={}", config.stage0_metadata.config.git_merge_commit_email).into(),
-            "-n1".into(),
-            "--first-parent".into(),
-            closest_upstream.into(),
-            "--".into(),
-            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"),
-        ]);
-        output(&mut rev_list.command).trim().to_owned()
+        get_closest_merge_base_commit(
+            Some(&config.src),
+            &config.git_config(),
+            &config.stage0_metadata.config.git_merge_commit_email,
+            &[
+                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()
     } else if let Some(info) = channel::read_commit_info_file(&config.src) {
         info.sha.trim().to_owned()
     } else {

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

@@ -20,7 +20,7 @@ use crate::core::build_steps::llvm;
 use crate::core::config::flags::{Color, Flags, Warnings};
 use crate::utils::cache::{Interned, INTERNER};
 use crate::utils::channel::{self, GitInfo};
-use crate::utils::helpers::{self, exe, output, t};
+use crate::utils::helpers::{self, exe, get_closest_merge_base_commit, output, t};
 use build_helper::exit;
 use serde::{Deserialize, Deserializer};
 use serde_derive::Deserialize;
@@ -2455,14 +2455,14 @@ impl Config {
 
         // Look for a version to compare to based on the current commit.
         // Only commits merged by bors will have CI artifacts.
-        let merge_base = output(
-            &mut helpers::git(Some(&self.src))
-                .arg("rev-list")
-                .arg(format!("--author={}", self.stage0_metadata.config.git_merge_commit_email))
-                .args(["-n1", "--first-parent", "HEAD"])
-                .command,
-        );
-        let commit = merge_base.trim_end();
+        let commit = get_closest_merge_base_commit(
+            Some(&self.src),
+            &self.git_config(),
+            &self.stage0_metadata.config.git_merge_commit_email,
+            &[],
+        )
+        .unwrap();
+
         if commit.is_empty() {
             println!("ERROR: could not find commit hash for downloading rustc");
             println!("HELP: maybe your repository history is too shallow?");
@@ -2473,7 +2473,7 @@ impl Config {
 
         // Warn if there were changes to the compiler or standard library since the ancestor commit.
         let has_changes = !t!(helpers::git(Some(&self.src))
-            .args(["diff-index", "--quiet", commit, "--", &compiler, &library])
+            .args(["diff-index", "--quiet", &commit, "--", &compiler, &library])
             .command
             .status())
         .success();
@@ -2553,14 +2553,13 @@ impl Config {
 
         // Look for a version to compare to based on the current commit.
         // Only commits merged by bors will have CI artifacts.
-        let merge_base = output(
-            &mut helpers::git(Some(&self.src))
-                .arg("rev-list")
-                .arg(format!("--author={}", self.stage0_metadata.config.git_merge_commit_email))
-                .args(["-n1", "--first-parent", "HEAD"])
-                .command,
-        );
-        let commit = merge_base.trim_end();
+        let commit = get_closest_merge_base_commit(
+            Some(&self.src),
+            &self.git_config(),
+            &self.stage0_metadata.config.git_merge_commit_email,
+            &[],
+        )
+        .unwrap();
         if commit.is_empty() {
             println!("error: could not find commit hash for downloading components from CI");
             println!("help: maybe your repository history is too shallow?");
@@ -2571,7 +2570,7 @@ impl Config {
 
         // Warn if there were changes to the compiler or standard library since the ancestor commit.
         let mut git = helpers::git(Some(&self.src));
-        git.args(["diff-index", "--quiet", commit, "--"]);
+        git.args(["diff-index", "--quiet", &commit, "--"]);
 
         for path in modified_paths {
             git.arg(format!("{top_level}/{path}"));

src/bootstrap/src/utils/helpers.rs

@@ -3,6 +3,7 @@
 //! Simple things like testing the various filesystem operations here and there,
 //! not a lot of interesting happenings here unfortunately.
 
+use build_helper::git::{get_git_merge_base, output_result, GitConfig};
 use build_helper::util::fail;
 use std::env;
 use std::ffi::OsStr;
@@ -520,3 +521,26 @@ pub fn git(source_dir: Option<&Path>) -> BootstrapCommand {
 
     git
 }
+
+/// Returns the closest commit available from upstream for the given `author` and `target_paths`.
+///
+/// If it fails to find the commit from upstream using `git merge-base`, fallbacks to HEAD.
+pub fn get_closest_merge_base_commit(
+    source_dir: Option<&Path>,
+    config: &GitConfig<'_>,
+    author: &str,
+    target_paths: &[PathBuf],
+) -> Result<String, String> {
+    let merge_base = get_git_merge_base(config, source_dir).unwrap_or_else(|_| "HEAD".into());
+
+    let mut git = git(source_dir);
+
+    git.arg(Path::new("rev-list"));
+    git.args([&format!("--author={author}"), "-n1", "--first-parent", &merge_base]);
+    if !target_paths.is_empty() {
+        git.arg("--");
+        git.args(target_paths);
+    }
+
+    Ok(output_result(&mut git.command)?.trim().to_owned())
+}

src/tools/build_helper/src/git.rs

@@ -7,7 +7,7 @@ pub struct GitConfig<'a> {
 }
 
 /// Runs a command and returns the output
-fn output_result(cmd: &mut Command) -> Result<String, String> {
+pub fn output_result(cmd: &mut Command) -> Result<String, String> {
     let output = match cmd.stderr(Stdio::inherit()).output() {
         Ok(status) => status,
         Err(e) => return Err(format!("failed to run command: {:?}: {}", cmd, e)),