build_helper: handle emails containing square brackets

The `git` API shells out to `git rev-list` and was directly passing an
email string to the command's `--author` flag. That flag interprets its
arguments as a regular expression, meaning that characters like square
brackets (`[]`) in the email string made the command fail to find a
commit matching the author e-mail

This commit escapes the email string prior to passing it to `git
rev-list`.

The change is tested in the `bootstrap` crate because it contains the
testing infrastructure to create temporary git repositories.

fixes #140669

Author: japaric

src/bootstrap/src/core/builder/tests.rs

@@ -1,6 +1,8 @@
 use std::env::VarError;
 use std::{panic, thread};
 
+use build_helper::ci::CiEnv;
+use build_helper::git::GitConfig;
 use build_helper::stage0_parser::parse_stage0_file;
 use llvm::prebuilt_llvm_config;
 
@@ -267,6 +269,35 @@ fn ci_rustc_if_unchanged_invalidate_on_library_changes_in_ci() {
     });
 }
 
+// this test is similar to the other two `ci_rustc_if_unchanged_` tests below but overrides
+// `merge_bot_email`. it uses the lower level `build_helper::git` API because
+// `parse_config_download_rustc_at` is hard-coded to use the `git_merge_commit_email` value in
+// the git-tracked file `/src/stage0`
+#[test]
+fn ci_rustc_with_square_bracket_in_author_email() {
+    git_test(|ctx| {
+        let author_email = "bors[bot]@example.com";
+        ctx.merge_bot_email = format!("Merge bot <{}>", author_email);
+        ctx.write("src/ci/channel", "nightly");
+        ctx.commit();
+
+        let sha = ctx.create_upstream_merge(&["compiler/bar"]);
+
+        let git_config = GitConfig {
+            git_repository: &ctx.git_repo,
+            nightly_branch: &ctx.nightly_branch,
+            git_merge_commit_email: author_email,
+        };
+        let got = build_helper::git::get_closest_upstream_commit(
+            Some(ctx.get_path()),
+            &git_config,
+            CiEnv::None,
+        );
+
+        assert_eq!(got, Ok(Some(sha)));
+    });
+}
+
 #[test]
 fn ci_rustc_if_unchanged_do_not_invalidate_on_library_changes_outside_ci() {
     git_test(|ctx| {

src/build_helper/src/git.rs

@@ -9,6 +9,16 @@ pub struct GitConfig<'a> {
     pub git_merge_commit_email: &'a str,
 }
 
+impl GitConfig<'_> {
+    // prepares `git_merge_commit_email` before it gets passed to `git rev-list`'s `--author` flag
+    //
+    // the `--author` flag takes a "pattern" (regular expression) not a substring so any
+    // square bracket in the original email needs to be escaped
+    fn author_email(&self) -> String {
+        self.git_merge_commit_email.replace('[', "\\[").replace(']', "\\]")
+    }
+}
+
 /// Runs a command and returns the output
 pub fn output_result(cmd: &mut Command) -> Result<String, String> {
     let output = match cmd.stderr(Stdio::inherit()).output() {
@@ -183,7 +193,7 @@ fn get_latest_upstream_commit_that_modified_files(
         "-n1",
         &upstream,
         "--author",
-        git_config.git_merge_commit_email,
+        &git_config.author_email(),
     ]);
 
     if !target_paths.is_empty() {
@@ -227,13 +237,7 @@ fn get_closest_upstream_commit(
     // chronologically recent bors commit.
     // Here we assume that none of our subtrees use bors anymore, and that all their old bors
     // commits are way older than recent rustc bors commits!
-    git.args([
-        "rev-list",
-        "--author-date-order",
-        &format!("--author={}", config.git_merge_commit_email),
-        "-n1",
-        &base,
-    ]);
+    git.args(["rev-list", "--author-date-order", "--author", &config.author_email(), "-n1", &base]);
 
     let output = output_result(&mut git)?.trim().to_owned();
     if output.is_empty() { Ok(None) } else { Ok(Some(output)) }