[PATCH v5] [GSOC] ref-filter: fix read invalid union member bug

From: ZheNing Hu <adlternative@gmail.com>

used_atom.u is an union, and it has different members depending on what atom the auxiliary data the union part of the "struct used_atom" wants to record. At most only one of the members can be valid at any one time. Since the code checks u.remote_ref without even making sure if the atom is "push" or "push:" (which are only two cases that u.remote_ref.push becomes valid), but u.remote_ref shares the same storage for other members of the union, the check was reading from an invalid member, which was the bug.

Modify the condition here to check whether the atom name equals to "push" or starts with "push:", to avoid reading the value of invalid member of the union.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: ZheNing Hu <adlternative@gmail.com>
---
    [GSOC] ref-filter: fix read invalid union member bug
    
    I and Junio discussed the situation that this bug might actually occur.
    
    The damage that can be found currently is using %(colors:#aa22ac) or
    some other %(colors) atoms. But Junio found that testing
    %(colors:#aa22ac) alone did not show the expected bug in the commit
    before the repair.
    
    So I conducted an experiment:
    
    When we use git push, Git will add some config, these configurations
    will affect the result of the execution process related to atom %(push)
    in populate_value().
    
    Change from last version: added a new test, which added two
    configurations:
    
    git config branch.main.remote origin git config branch.main.merge
    refs/heads/main
    
    used to simulate the configuration changes brought by git push.
    
    Finally, a test on the broken atom %(colors:#aa22ac). In the commit
    before the repair, breakage occurs. In the commit after the repair,
    breakage disappeared.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-949%2Fadlternative%2Fref-filter-enum-bug-fix-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-949/adlternative/ref-filter-enum-bug-fix-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/949

Range-diff vs v4:

 1:  8c6c0368a590 ! 1:  b546477e8c87 [GSOC] ref-filter: fix read invalid union member bug
     @@ t/t6302-for-each-ref-filter.sh: test_expect_success '%(color) must fail' '
       	test_must_fail git for-each-ref --format="%(color)%(refname)"
       '
       
     -+test_expect_success '%(color:#aa22ac) must success' '
     ++test_expect_success '%(color:#aa22ac) must successed' '
     ++	test_when_finished "cd .. && rm -rf ./test" &&
     ++	mkdir test &&
     ++	cd test &&
     ++	git init &&
      +	cat >expect <<-\EOF &&
      +	refs/heads/main
     -+	refs/heads/side
     -+	refs/odd/spot
     -+	refs/tags/annotated-tag
     -+	refs/tags/doubly-annotated-tag
     -+	refs/tags/doubly-signed-tag
     -+	refs/tags/four
     -+	refs/tags/one
     -+	refs/tags/signed-tag
     -+	refs/tags/three
     -+	refs/tags/two
      +	EOF
     ++	git add . &&
     ++	git branch -M main &&
     ++	git commit -m "test" &&
     ++	git remote add origin nowhere &&
     ++	git config branch.main.remote origin &&
     ++	git config branch.main.merge refs/heads/main &&
      +	git for-each-ref --format="%(color:#aa22ac)%(refname)" >actual &&
      +	test_cmp expect actual
      +'

 ref-filter.c                   |  2 +-
 t/t6302-for-each-ref-filter.sh | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)