Unrolled build for #148500

Rollup merge of #148500 - Kobzol:git-update-inex, r=jieyouxu

Update git index before running diff-index

Discussed in https://rust-lang.zulipchat.com/#narrow/channel/326414-t-infra.2Fbootstrap/topic/tidy.3A.20strange.20number.20of.20modified.20files/with/553714742.

This is apparently the cause of `x test tidy` printing weird number of formatted files, and also of sometimes quirky behavior of finding the files modified from a base commit.

Author: rust-timer

src/build_helper/src/git.rs

@@ -143,14 +143,13 @@ pub fn check_path_modifications(
 
 /// Returns true if any of the passed `paths` have changed since the `base` commit.
 pub fn has_changed_since(git_dir: &Path, base: &str, paths: &[&str]) -> bool {
-    let mut git = Command::new("git");
-    git.current_dir(git_dir);
+    run_git_diff_index(Some(git_dir), |cmd| {
+        cmd.args(["--quiet", base, "--"]).args(paths);
 
-    git.args(["diff-index", "--quiet", base, "--"]).args(paths);
-
-    // Exit code 0 => no changes
-    // Exit code 1 => some changes were detected
-    !git.status().expect("cannot run git diff-index").success()
+        // Exit code 0 => no changes
+        // Exit code 1 => some changes were detected
+        !cmd.status().expect("cannot run git diff-index").success()
+    })
 }
 
 /// Returns the latest upstream commit that modified `target_paths`, or `None` if no such commit
@@ -267,31 +266,49 @@ pub fn get_git_modified_files(
         return Err("No upstream commit was found".to_string());
     };
 
-    let mut git = Command::new("git");
-    if let Some(git_dir) = git_dir {
-        git.current_dir(git_dir);
-    }
-    let files = output_result(git.args(["diff-index", "--name-status", merge_base.trim()]))?
-        .lines()
-        .filter_map(|f| {
-            let (status, name) = f.trim().split_once(char::is_whitespace).unwrap();
-            if status == "D" {
-                None
-            } else if Path::new(name).extension().map_or(extensions.is_empty(), |ext| {
-                // If there is no extension, we allow the path if `extensions` is empty
-                // If there is an extension, we allow it if `extension` is empty or it contains the
-                // extension.
-                extensions.is_empty() || extensions.contains(&ext.to_str().unwrap())
-            }) {
-                Some(name.to_owned())
-            } else {
-                None
-            }
-        })
-        .collect();
+    let files = run_git_diff_index(git_dir, |cmd| {
+        output_result(cmd.args(["--name-status", merge_base.trim()]))
+    })?
+    .lines()
+    .filter_map(|f| {
+        let (status, name) = f.trim().split_once(char::is_whitespace).unwrap();
+        if status == "D" {
+            None
+        } else if Path::new(name).extension().map_or(extensions.is_empty(), |ext| {
+            // If there is no extension, we allow the path if `extensions` is empty
+            // If there is an extension, we allow it if `extension` is empty or it contains the
+            // extension.
+            extensions.is_empty() || extensions.contains(&ext.to_str().unwrap())
+        }) {
+            Some(name.to_owned())
+        } else {
+            None
+        }
+    })
+    .collect();
     Ok(files)
 }
 
+/// diff-index can return outdated information, because it does not update the git index.
+/// This function uses `update-index` to update the index first, and then provides `func` with a
+/// command prepared to run `git diff-index`.
+fn run_git_diff_index<F, T>(git_dir: Option<&Path>, func: F) -> T
+where
+    F: FnOnce(&mut Command) -> T,
+{
+    let git = || {
+        let mut git = Command::new("git");
+        if let Some(git_dir) = git_dir {
+            git.current_dir(git_dir);
+        }
+        git
+    };
+
+    // We ignore the exit code, as it errors out when some files are modified.
+    let _ = output_result(git().args(["update-index", "--refresh", "-q"]));
+    func(git().arg("diff-index"))
+}
+
 /// Returns the files that haven't been added to git yet.
 pub fn get_git_untracked_files(git_dir: Option<&Path>) -> Result<Option<Vec<String>>, String> {
     let mut git = Command::new("git");