merge: introduce a preresolve function The section of code that writes out the version of the file cached in the merge state should only be run at preresolve time. This is so that if the premerge keeps around conflict markers, those don't get overwritten before the main merge.

merge.mergestate._resolve: also return completed status We'll need this for a new 'preresolve' function we're adding.

merge.mergestate: add a wrapper around resolve The resolve function will be broken up into separate pre-resolve and resolve steps.

simplemerge: move conflict warning message to filemerge The current output for a failed merge with conflict markers looks something like: merging foo warning: conflicts during merge. merging foo incomplete! (edit conflicts, then use 'hg resolve --mark') merging bar warning: conflicts during merge. merging bar incomplete! (edit conflicts, then use 'hg resolve --mark') We're going to change the way merges are done to perform all premerges before all merges, so that the output above would look like: merging foo merging bar warning: conflicts during merge. merging foo incomplete! (edit conflicts, then use 'hg resolve --mark') warning: conflicts during merge. merging bar incomplete! (edit conflicts, then use 'hg resolve --mark') The 'warning: conflicts during merge' line has no context, so is pretty confusing. This patch will change the future output to: merging foo merging bar warning: conflicts while merging foo! (edit, then use 'hg resolve --mark') warning: conflicts while merging bar! (edit, then use 'hg resolve --mark') The hint on how to resolve the conflicts makes this a bit unwieldy, but solving that is tricky because we already hint that people run 'hg resolve' to retry unresolved merges. The 'hg resolve --mark' mostly applies to conflict marker based resolution.

filemerge: clean up some dead code We now exit early if we do a premerge, so extra checks are no longer necessary.

run-tests: add b-prefix on two strings to fix python3 support

filemerge: break overall filemerge into separate premerge and merge steps This means that in ms.resolve we must call merge after calling premerge. This doesn't yet mean that all premerges happen before any merges -- however, this does get us closer to our goal. The output differences are because we recompute the merge tool. The only user-visible difference caused by this patch is that if the tool is missing we'll print the warning twice. Not a huge deal, though.

filemerge: only copy to backup during premerge step The premerge might leave the original file in an unclean state. Therefore it's important to only copy the file in the beginning.