simplemerge: stop merging file flags As 384df4db6520 (merge: merge file flags together with file content, 2013-01-09) explains, we shouldn't do a 3-way merge of the symlink. However, since 84614212ae39 (flags: actually merge flags in simplemerge, 2020-05-16), we do that in `simplemerge.simplemerge()`. What's more, the merging of the executable flag there isn't actually necessary; it was made a no-op by the very next commit, i.e. 4234c9af515d (flags: read flag from dirstate/disk for workingcopyctx (issue5743), 2020-05-16). I found the overall flag-merging code (not the bit in `simplemerge.py`) very hard to follow, but I think I now finally understand how it works. `mergestate.resolve()` calculates the merged file flags and sets them on the local side of the merge (confusingly by calling `_restore_backup()`). Then it calls `filemerge.filemerge()`, which in turn calls `simplemerge.simplemerge()` (if premerge is enabled). That means that the flags on the local side `fcs.flags()` are already correct when the flag-merging code in `simplemerge.simplemerge()` runs. Interestingly, that code still works when the local side already has the merged value, it just doesn't change the value. Here's a truth table to explain why: ``` BLOMCAR 0000000 0011111 0101011 0111111 1000000 1010000 1100000 1111101 ``` B: Base L: Local O: Other M: Merged flags from `mergestate.resolve()`, i.e. what's called "local" when we get to `simplemerge.simplemerge()` C: `commonflags` in `simplemerge.simplemerge()`, i.e. `M & O` A: `addedflags` in `simplemerge.simplemerge()`, i.e. `(M ^ O) - B` R: Re-merged flags `simplemerge.simplemerge()`, i.e. `C | A` As you can see, the re-merged flags are always unchanged compared to the initial merged flags (R equals M). Therefore, this patch effectively backs out 84614212ae39. (I might later refactor this code to have the flags explicitly passed in.) `simplemerge.simplemerge()` is also called from `contrib/simplemerge.py`, but that code never passes any flags. Differential Revision: https://phab.mercurial-scm.org/D11879