[PATCH] blame: respect .git-blame-ignore-revs automatically

["Abhijeetsingh Meena via GitGitGadget" <gitgitgadget@gmail.com>]

From: Abhijeetsingh Meena <abhijeet040403@gmail.com>

Modify `git blame` to automatically respect a `.git-blame-ignore-revs`
file if it exists in the repository. This file is used by many projects
to ignore non-functional changes, such as reformatting or large-scale
refactoring, when generating blame information.

Before this change, users had to manually specify the file with the
`--ignore-revs-file` option. This update streamlines the process by
automatically detecting the `.git-blame-ignore-revs` file, reducing
manual effort.

This change aligns with the standardized practice in many repositories
and simplifies the workflow for users.

Signed-off-by: Abhijeetsingh Meena <abhijeet040403@gmail.com>
---
    blame: respect .git-blame-ignore-revs automatically
    
    
    Introduction
    ============
    
    Hi, I'm Abhijeet (Ethan0456), and this is my first contribution to the
    Git project. I currently work as an ML Engineer at an early-stage
    startup, and I’m excited to contribute to this open-source project.
    
    
    Why the Change?
    ===============
    
    I came across this enhancement request on the bug tracker and found it
    beginner-friendly, making it a great opportunity for me to get familiar
    with the Git codebase. The ability for git blame to automatically
    respect the .git-blame-ignore-revs file is something that can streamline
    workflows for many users, and I felt it would be a valuable addition.
    
    
    Feedback
    ========
    
    While I’m confident in the changes made to builtin/blame.c and the new
    test case in t/t8015-blame-ignore-revs.sh, I welcome any feedback or
    suggestions to improve both my code and approach. I’m eager to learn
    from the community and improve where needed.
    
    
    Community Need
    ==============
    
    There is precedent for this functionality in other projects:
    
     * Chromium
       [https://chromium.googlesource.com/chromium/src.git/+/f0596779e57f46fccb115a0fd65f0305894e3031/.git-blame-ignore-revs],
       which powers many popular browsers, uses .git-blame-ignore-revs to
       simplify the blame process by ignoring non-functional changes.
     * Rob Allen's blog post
       [https://akrabat.com/ignoring-revisions-with-git-blame/] discusses
       the need for ignoring revisions with git blame, and a commenter
       specifically suggests that it would be helpful if Git automatically
       respected .git-blame-ignore-revs.
    
    I hope this change aligns with community needs and improves the git
    blame experience for users.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1809%2FEthan0456%2Fblame-auto-ignore-revs-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1809/Ethan0456/blame-auto-ignore-revs-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1809

 builtin/blame.c                      |  8 ++++++++
 t/t8015-blame-default-ignore-revs.sh | 26 ++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100755 t/t8015-blame-default-ignore-revs.sh

diff --git a/builtin/blame.c b/builtin/blame.c
index e407a22da3b..1eddabaf60f 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1105,6 +1105,14 @@ parse_done:
 		add_pending_object(&revs, &head_commit->object, "HEAD");
 	}
 
+	/*
+	* By default, add .git-blame-ignore-revs to the list of files
+	* containing revisions to ignore if it exists.
+	*/
+	if (access(".git-blame-ignore-revs", F_OK) == 0) {
+		string_list_append(&ignore_revs_file_list, ".git-blame-ignore-revs");
+	}
+
 	init_scoreboard(&sb);
 	sb.revs = &revs;
 	sb.contents_from = contents_from;
diff --git a/t/t8015-blame-default-ignore-revs.sh b/t/t8015-blame-default-ignore-revs.sh
new file mode 100755
index 00000000000..84e1a9e87e6
--- /dev/null
+++ b/t/t8015-blame-default-ignore-revs.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+
+test_description='default revisions to ignore when blaming'
+
+TEST_PASSES_SANITIZE_LEAK=true
+. ./test-lib.sh
+
+test_expect_success 'blame: default-ignore-revs-file' '
+    test_commit first-commit hello.txt hello &&
+
+    echo world >>hello.txt &&
+    test_commit second-commit hello.txt &&
+
+    sed "1s/hello/hi/" <hello.txt > hello.txt.tmp &&
+    mv hello.txt.tmp hello.txt &&
+    test_commit third-commit hello.txt &&
+
+    git rev-parse HEAD >ignored-file &&
+    git blame --ignore-revs-file=ignored-file hello.txt >expect &&
+    git rev-parse HEAD >.git-blame-ignore-revs &&
+    git blame hello.txt >actual &&
+
+    test_cmp expect actual
+'
+
+test_done
\ No newline at end of file

base-commit: 777489f9e09c8d0dd6b12f9d90de6376330577a2
-- 
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