From 1fe3502e9590477be84ed3b739df956bc666d11b Mon Sep 17 00:00:00 2001
From: Daniel Baker <daniel.n.baker@gmail.com>
Date: Sat, 14 Dec 2024 21:53:42 -0800
Subject: [PATCH] genemichaels: apply patch to only write files if changed

When formatting rust files with `genemichaels`, the timestamp of the
file is always modified whether or not the file was changed. This is
problematic for detecting whether a file has been reformatted or not,
such as when using tools such as `pre-commit`, `treefmt`, and
`treefmt-nix`.

See the following:
https://github.com/andrewbaxter/genemichaels/issues/95
https://github.com/andrewbaxter/genemichaels/pull/96
https://github.com/numtide/treefmt-nix/pull/277
---
 .../genemichaels-only-write-if-changed.patch  | 20 +++++++++++++++++++
 pkgs/by-name/ge/genemichaels/package.nix      |  8 ++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 pkgs/by-name/ge/genemichaels/genemichaels-only-write-if-changed.patch

diff --git a/pkgs/by-name/ge/genemichaels/genemichaels-only-write-if-changed.patch b/pkgs/by-name/ge/genemichaels/genemichaels-only-write-if-changed.patch
new file mode 100644
index 0000000000000..65841f8bbe4ca
--- /dev/null
+++ b/pkgs/by-name/ge/genemichaels/genemichaels-only-write-if-changed.patch
@@ -0,0 +1,20 @@
+diff --git a/crates/genemichaels/src/main.rs b/crates/genemichaels/src/main.rs
+index 724b38a..2fb23d0 100644
+--- a/crates/genemichaels/src/main.rs
++++ b/crates/genemichaels/src/main.rs
+@@ -348,10 +348,11 @@ impl FormatPool {
+                     log.log_with(loga::INFO, "Skipping due to skip comment", ea!());
+                     return Ok(());
+                 }
+-                fs::write(
+-                    &file,
+-                    process_file_contents(log, &config, &source).context("Error doing formatting")?.as_bytes(),
+-                ).context("Error writing formatted code back")?;
++                let processed = process_file_contents(log, &config, &source).context("Error doing formatting")?;
++                if source != processed {
++                    log.log_with(loga::INFO, "Writing newly file", ea!());
++                    fs::write(&file, processed.as_bytes()).context("Error writing formatted code back")?;
++                }
+                 return Ok(());
+             }).stack_context(log, "Error formatting file");
+             match res {
diff --git a/pkgs/by-name/ge/genemichaels/package.nix b/pkgs/by-name/ge/genemichaels/package.nix
index 557e17934a283..2daa4dbbc74f2 100644
--- a/pkgs/by-name/ge/genemichaels/package.nix
+++ b/pkgs/by-name/ge/genemichaels/package.nix
@@ -15,6 +15,14 @@ rustPlatform.buildRustPackage rec {
     hash = "sha256-qPyIC9AbRQI+inBft7Dd5R5v+tXtJcZdiV4lBIBwpyM=";
   };
 
+  patches = [
+    # TODO(@djacu): remove this if this patch is merged and the version is
+    # bumped to a release that has this change
+    # See: https://github.com/andrewbaxter/genemichaels/issues/95
+    # See: https://github.com/andrewbaxter/genemichaels/pull/96
+    ./genemichaels-only-write-if-changed.patch
+  ];
+
   cargoHash = "sha256-yPxgYf8N3Dqns/uKhdM++jpzG7zTPhCVVq+7WA9G/SM=";
 
   cargoBuildFlags = [ "--package ${pname}" ];