Re: [bug] git log --invert-grep --grep=[sufficiently complicated regex] prints nothing

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Zack

On 23/11/2022 20:17, Zack Weinberg wrote:
> I’m attempting to have my blog, which is a static site generated from
> a bunch of Markdown files stored in git, automatically pull the
> the most recent modification date for each page out of the git history.
> The idea is to use ‘git log --follow --pretty=tformat:'%ct' <file>‘ on
> each file and then use the oldest reported timestamp as the creation
> date and the newest reported timestamp as the last modification date.
> 
> But there’s a catch: there are commits I want to ignore in this
> calculation, such as mechanical changes applied to the entire site.
> And this brings me to the bug: --invert-grep doesn’t work correctly
> when the --grep regex is sufficiently complicated.
> 
> Here's the complete set of commits that modified an example file:
> 
> $ git log --follow --pretty=tformat:'%ct %s' \
>    src/posts/uncat/unearthed-arcana-music-division.md
> 1668545053 Begin restoring the site structure.
> 1668545051 Reorganize directory tree prior to setting up Metalsmith
> 1668545032 Mechanically convert Pandoc to standard YAML metadata delimiters.
> 1610735533 Mechanically convert to properly delimited YAML metadata.
> 1417101173 Correct slug for Uncategorized.
> 1417050416 The Great Dead and Moved Link Cleanup of 2014.
> 1416938128 Use category_meta plugin to fix category slugs.
> 1416763607 Initial import of content and Pelican skeleton.
> 
> And here's an application of --grep that prints only the commits I _don't_ want:
> 
> $ git log --follow -E --pretty=tformat:'%ct %s' \
>    --grep='^(Mechanically convert|Begin restoring the site structure|Reorganize directory tree)' \
>   src/posts/uncat/unearthed-arcana-music-division.md
> 1668545053 Begin restoring the site structure.
> 1668545051 Reorganize directory tree prior to setting up Metalsmith
> 1668545032 Mechanically convert Pandoc to standard YAML metadata delimiters.
> 1610735533 Mechanically convert to properly delimited YAML metadata.
> 
> Theoretically, adding --invert-grep to that should make it print the
> commits I do want, but instead it prints nothing at all:

I think the problem is that you are excluding the commit that renames 
the file and that stops --follow from following the rename. See below 
for a simple reproduction using git's test suite. I'm afraid I'm not 
familiar with the --follow code so I've no idea how to fix this.

Best Wishes

Phillip

---- >8 ----
#!/bin/sh

test_description='Demonstrate `git log --follow --grep` failure'

. ./test-lib.sh

test_expect_failure '--grep breaks --follow' '
	test_commit first file-a "$(seq 1 100)" &&
	git rm file-a &&
	test_commit second file-b "$(seq 2 101)" &&
	test_commit third file-b "$(seq 3 102)" &&
	git log --follow --grep "^first" file-b >actual &&
	git log first >expect &&
	test_cmp expect actual
'

test_expect_success '--grep breaks --follow' '
	git log --follow -E --grep "^(first|second)" file-b >actual &&
	git log second >expect &&
	test_cmp expect actual
'

test_done