Move items related to computing diffs to a separate file

[Nicholas-Baron]

Work towards #89475.

[rust-highfive]

r? @Mark-Simulacrum

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[Mark-Simulacrum]

There's some diff-related code here as well -

rust/src/tools/compiletest/src/runtest.rs

Line 2404 in cb501a6

let diff_filename = format!("build/tmp/rustdoc-compare-{}.diff", std::process::id());

I'm not sure how much that is "the same" or can be unified, haven't looked too closely. What do you think?

[Nicholas-Baron]

@Mark-Simulacrum While this does seem diff-related, its structure is very different from write_diff and make_diff, suggesting some semantic differences. This makes unification a task I think beyond this PR.

It may be possible to extract some parts as separate functions, as self is not reference heavily in them. However, this may be beyond the scope of this PR as well. The following code block is an example.

rust/src/tools/compiletest/src/runtest.rs

Lines 2406 to 2431 in cb501a6

	{
	let mut diff_output = File::create(&diff_filename).unwrap();
	let mut wrote_data = false;
	for entry in walkdir::WalkDir::new(out_dir) {
	let entry = entry.expect("failed to read file");
	let extension = entry.path().extension().and_then(|p| p.to_str());
	if entry.file_type().is_file()
	&& (extension == Some("html".into()) || extension == Some("js".into()))
	{
	let expected_path =
	compare_dir.join(entry.path().strip_prefix(&out_dir).unwrap());
	let expected =
	if let Ok(s) = std::fs::read(&expected_path) { s } else { continue };
	let actual_path = entry.path();
	let actual = std::fs::read(&actual_path).unwrap();
	let diff = unified_diff::diff(
	&expected,
	&expected_path.to_string_lossy(),
	&actual,
	&actual_path.to_string_lossy(),
	3,
	);
	wrote_data |= !diff.is_empty();
	diff_output.write_all(&diff).unwrap();
	}
	}

[Mark-Simulacrum]

Hm. Ok. Well, I guess we can add a "why do we have two different diff implementations" (unified-diff and diff crates) to the list of open questions...

But regardless I think much of the code can be moved into this module, if not unified just yet -- it looks pretty separate from being rustdoc specific to me, beyond the minor filter on extensions (which seems easy to pass in).

[Mark-Simulacrum]

@bors r+ rollup

[bors]

📌 Commit 3760c91 has been approved by Mark-Simulacrum