resolve: fix mark-check when a file was deleted on one side (issue6020)

wvfs.open raises an error if one of the files does not exist. Ignoring the error
if it's ENOENT is done in several other places in this code, so I'm in good
company :)

Differential Revision: https://phab.mercurial-scm.org/D5243

mercurial/commands.py

@@ -4935,8 +4935,7 b' def resolve(ui, repo, *pats, **opts):'
 
             if mark:
                 if markcheck:
-                    with repo.wvfs(f) as fobj:
-                        fdata = fobj.read()
+                    fdata = repo.wvfs.tryread(f)
                     if filemerge.hasconflictmarkers(fdata) and \
                         ms[f] != mergemod.MERGE_RECORD_RESOLVED:
                         hasconflictmarkers.append(f)

tests/test-resolve.t

@@ -629,3 +629,169 b' Test that commands.resolve.confirm respe'
 
 Done with commands.resolve.confirm tests:
   $ cd ..
+
+Test that commands.resolve.mark-check works even if there are deleted files:
+  $ hg init resolve-deleted
+  $ cd resolve-deleted
+  $ echo r0 > file1
+  $ hg ci -qAm r0
+  $ echo r1 > file1
+  $ hg ci -qm r1
+  $ hg co -qr 0
+  $ hg rm file1
+  $ hg ci -qm "r2 (delete file1)"
+
+(At this point we have r0 creating file1, and sibling commits r1 and r2, which
+ modify and delete file1, respectively)
+
+  $ hg merge -r 1
+  file 'file1' was deleted in local [working copy] but was modified in other [merge rev].
+  What do you want to do?
+  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? u
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+  $ hg resolve --list
+  U file1
+Because we left it as 'unresolved' the file should still exist.
+  $ [ -f file1 ] || echo "File does not exist?"
+BC behavior: `hg resolve --mark` accepts that the file is still there, and
+doesn't have a problem with this situation.
+  $ hg resolve --mark --config commands.resolve.mark-check=abort
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+The file is still there:
+  $ [ -f file1 ] || echo "File does not exist?"
+Let's check mark-check=warn:
+  $ hg resolve --unmark file1
+  $ hg resolve --mark --config commands.resolve.mark-check=warn
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+The file is still there:
+  $ [ -f file1 ] || echo "File does not exist?"
+Let's resolve the issue by deleting the file via `hg resolve`
+  $ hg resolve --unmark file1
+  $ echo 'd' | hg resolve file1 --config ui.interactive=1
+  file 'file1' was deleted in local [working copy] but was modified in other [merge rev].
+  What do you want to do?
+  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? d
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+The file is deleted:
+  $ [ -f file1 ] && echo "File still exists?" || true
+Doing `hg resolve --mark` doesn't break now that the file is missing:
+  $ hg resolve --mark --config commands.resolve.mark-check=abort
+  (no more unresolved files)
+  $ hg resolve --mark --config commands.resolve.mark-check=warn
+  (no more unresolved files)
+Resurrect the file, and delete it outside of hg:
+  $ hg resolve --unmark file1
+  $ hg resolve file1
+  file 'file1' was deleted in local [working copy] but was modified in other [merge rev].
+  What do you want to do?
+  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? u
+  [1]
+  $ [ -f file1 ] || echo "File does not exist?"
+  $ hg resolve --list
+  U file1
+  $ rm file1
+  $ hg resolve --mark --config commands.resolve.mark-check=abort
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+  $ hg resolve --unmark file1
+  $ hg resolve file1
+  file 'file1' was deleted in local [working copy] but was modified in other [merge rev].
+  What do you want to do?
+  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? u
+  [1]
+  $ [ -f file1 ] || echo "File does not exist?"
+  $ hg resolve --list
+  U file1
+  $ rm file1
+  $ hg resolve --mark --config commands.resolve.mark-check=warn
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+
+
+For completeness, let's try that in the opposite direction (merging r2 into r1,
+instead of r1 into r2):
+  $ hg update -qCr 1
+  $ hg merge -r 2
+  file 'file1' was deleted in other [merge rev] but was modified in local [working copy].
+  What do you want to do?
+  use (c)hanged version, (d)elete, or leave (u)nresolved? u
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+  $ hg resolve --list
+  U file1
+Because we left it as 'unresolved' the file should still exist.
+  $ [ -f file1 ] || echo "File does not exist?"
+BC behavior: `hg resolve --mark` accepts that the file is still there, and
+doesn't have a problem with this situation.
+  $ hg resolve --mark --config commands.resolve.mark-check=abort
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+The file is still there:
+  $ [ -f file1 ] || echo "File does not exist?"
+Let's check mark-check=warn:
+  $ hg resolve --unmark file1
+  $ hg resolve --mark --config commands.resolve.mark-check=warn
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+The file is still there:
+  $ [ -f file1 ] || echo "File does not exist?"
+Let's resolve the issue by deleting the file via `hg resolve`
+  $ hg resolve --unmark file1
+  $ echo 'd' | hg resolve file1 --config ui.interactive=1
+  file 'file1' was deleted in other [merge rev] but was modified in local [working copy].
+  What do you want to do?
+  use (c)hanged version, (d)elete, or leave (u)nresolved? d
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+The file is deleted:
+  $ [ -f file1 ] && echo "File still exists?" || true
+Doing `hg resolve --mark` doesn't break now that the file is missing:
+  $ hg resolve --mark --config commands.resolve.mark-check=abort
+  (no more unresolved files)
+  $ hg resolve --mark --config commands.resolve.mark-check=warn
+  (no more unresolved files)
+Resurrect the file, and delete it outside of hg:
+  $ hg resolve --unmark file1
+  $ hg resolve file1
+  file 'file1' was deleted in other [merge rev] but was modified in local [working copy].
+  What do you want to do?
+  use (c)hanged version, (d)elete, or leave (u)nresolved? u
+  [1]
+  $ [ -f file1 ] || echo "File does not exist?"
+  $ hg resolve --list
+  U file1
+  $ rm file1
+  $ hg resolve --mark --config commands.resolve.mark-check=abort
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+  $ hg resolve --unmark file1
+  $ hg resolve file1
+  file 'file1' was deleted in other [merge rev] but was modified in local [working copy].
+  What do you want to do?
+  use (c)hanged version, (d)elete, or leave (u)nresolved? u
+  [1]
+  $ [ -f file1 ] || echo "File does not exist?"
+  $ hg resolve --list
+  U file1
+  $ rm file1
+  $ hg resolve --mark --config commands.resolve.mark-check=warn
+  (no more unresolved files)
+  $ hg resolve --list
+  R file1
+
+  $ cd ..