merge: do early copy to deal with issue636 Without copies/renames, merges source names are 1:1 with their targets. Copies and renames introduce the possibility that there will be two merges with the same input but different output. By doing the copy to the destination name before the merge, the actual merge becomes 1:1 again, and no source is the input to two different merges. - add a preliminary scan to applyupdates to do copies - for the merge action, pass the old name (for finding ancestors) and the new name (for input to the merge) to filemerge - eliminate the old post-merge copy - lookup file contents from new name in filemerge - pass new name to external merge helper - report merge failure at new name - add a test

new file mode 100755
--- /dev/null
+++ b/tests/test-double-merge
@@ -0,0 +1,30 @@
+#!/bin/sh
+
+hg init repo
+cd repo
+
+echo line 1 > foo
+hg ci -qAm 'add foo' -d "1000000 0"
+
+# copy foo to bar and change both files
+hg cp foo bar
+echo line 2-1 >> foo
+echo line 2-2 >> bar
+hg ci -m 'cp foo bar; change both' -d "1000000 0"
+
+# in another branch, change foo in a way that doesn't conflict with
+# the other changes
+hg up -qC 0
+echo line 0 >| foo
+hg cat foo >> foo
+hg ci -m 'change foo' -d "1000000 0"
+
+# we get conflicts that shouldn't be there
+hg merge --debug
+
+echo "-- foo --"
+cat foo
+
+echo "-- bar --"
+cat bar
+