debugtagscache: verify that filenode is correct Previous patch from Matt demonstrates that `debugtagscache` does not warn about filenode being unknown which can be caused by a corrupted cache. We start by showing that it's an unknown node. Differential Revision: https://phab.mercurial-scm.org/D10015

tests: demonstrate a case where a corrupt tag cache causes an abort I happened to hit this trying to cover other cases around valid vs missing entries. I have no idea if this is something that could occur more naturally (similar to how a missing file node in `hgtagsfnodes1` can occur after a strip). There is a test just above this added in f5a7cf0adb12 mentioning it "overwrites the junk", though that tests truncation instead of actual garbage. But since this is just a cache, it probably shouldn't abort with a cryptic message like this. The two options I see both have downsides- either rebuild the cache (and potentially take a long time), or hint to the user to run a debug command. Differential Revision: https://phab.mercurial-scm.org/D9812

debugcommands: prevent using `is False` I was touching this code in a future patch and marmoute warned about usage of `is False` here. Quoting marmoute: ``` "is False" is going to check if the object you have the very same object in memory than the one Python allocated for False (in practice 0) This will "mostly work" on cpython because of implementation details, but is semantically wrong and can start breaking unexpectedly ``` Differential Revision: https://phab.mercurial-scm.org/D10014

hgtagsfnodes: refactor code to compute fnode into separate fn I plan to use this code at one more place while fixing a bug caused by an invalid fnode present in cache. Differential Revision: https://phab.mercurial-scm.org/D10013

error: remove shortening of node in error message This strips the complete 20 bytes node which was not found. Having the the full node in error message is important as it makes debugging easier. If a short node is to be displayed, that should be done by callers. Differential Revision: https://phab.mercurial-scm.org/D9994

copies: filter out copies grafted from another branch Consider this simple history: ``` @ 3 modify y | o 2 copy x to y, modify x | | o 1 copy x to y, modify x |/ o 0 add x ``` If we now rebase commit 3 onto 1, Mercurial will look for copies between commit 2 and commit 1. It does that by going backwards from 2 to 0 and then forwards from 0 to 1. It will find that x was copied to y, since that was what happened on the path between them (namely in commit 1). That leads Mercurial to do a 3-way merge between y@3 and y@1 with x@2 as base. We want to use y@2 as base instead. That's also what happened until commit 1d6d1a15. This patch fixes the regression by adding another filtering step when chaining copies via a diffbase. The new filtering step removes copies that were the same between the two branches (same source and destination, but not necessarily the same contents). Differential Revision: https://phab.mercurial-scm.org/D10120