Git fetcher: Don't create refs when fetching by revision #12386
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Git interprets them as part of the file name, so passing parameters like 'rev' breaks. Only relevant for testing (when _NIX_FORCE_HTTP is set) and local bare repos.
This causes Git to create a local ref named refs/head/<rev>, e.g. $ git -C ~/.cache/nix/gitv3/11irpim06vj4h6c0w8yls6kx4hvl0qd0gr1fvk47n76g6wf1s1vk ls-remote --symref . 5c4410e3b9891c05ab40d723de78c6f0be45ad30 refs/heads/5c4410e3b9891c05ab40d723de78c6f0be45ad30 7f6bde8a20de4cccc2256f088bc5af9dbe38881d refs/heads/7f6bde8a20de4cccc2256f088bc5af9dbe38881d which confuses readHead(), leading to errors like fatal: Refusing to point HEAD outside of refs/ warning: could not update cached head 'd275d93aa0bb8a004939b2f1e87f559f989453be' for 'file:///tmp/repo'
If we previously fetched by revision, the output of "git ls-remote" won't start with the expected line like ref: refs/heads/master HEAD but will be something like 5c4410e3b9891c05ab40d723de78c6f0be45ad30 refs/heads/5c4410e3b9891c05ab40d723de78c6f0be45ad30 This then causes Nix to treat that revision as a refname, which then leads to warnings like warning: could not update cached head '5c4410e3b9891c05ab40d723de78c6f0be45ad30' for 'file:///tmp/repo'
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Motivation
This fixes a couple of issues with the Git fetcher:
When fetching by revision, don't create a ref named
refs/head/<revision>. (This was caused by doinggit fetch <revision>:<revision>.) This is unnecessary and triggers the next bug.When parsing the output of
git ls-remote --symref, make sure that the first line referencesHEAD, otherwise a line likewill cause
5c44...(created by the previous bug) to be interpreted as a ref, leading to errors likefile://URLs. Git interprets them as part of the file name, so passing parameters likerevbreaks. Only relevant for testing (when_NIX_FORCE_HTTPis set) and local bare repos.Context
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