merge: implement --tool arguments using new ui.forcemerge configurable

ui.forcemerge is set before calling into merge or resolve commands, then unset
to prevent ui pollution for further operations.

ui.forcemerge takes precedence over HGMERGE, but mimics HGMERGE behavior if the
given --tool is not found by the merge-tools machinery.  This makes it possible
to do:  hg resolve --tool="python mymerge.py" FILE

With this approach, HGMERGE and ui.merge are not harmed by --tool

mercurial/commands.py

@@ -2586,12 +2586,6 b' def merge(ui, repo, node=None, **opts):'
     if not node:
         node = opts.get('rev')
 
-    t = opts.get('tool')
-    if t:
-        if 'HGMERGE' in os.environ:
-            os.environ['HGMERGE'] = ''
-        ui.setconfig('ui', 'merge', t)
-
     if not node:
         branch = repo.changectx(None).branch()
         bheads = repo.branchheads(branch)
@@ -2632,7 +2626,12 b' def merge(ui, repo, node=None, **opts):'
         displayer.close()
         return 0
 
-    return hg.merge(repo, node, force=opts.get('force'))
+    try:
+        # ui.forcemerge is an internal variable, do not document
+        ui.setconfig('ui', 'forcemerge', opts.get('tool', ''))
+        return hg.merge(repo, node, force=opts.get('force'))
+    finally:
+        ui.setconfig('ui', 'forcemerge', '')
 
 def outgoing(ui, repo, dest=None, **opts):
     """show changesets not found in the destination
@@ -2979,12 +2978,6 b' def resolve(ui, repo, *pats, **opts):'
         raise util.Abort(_('no files or directories specified; '
                            'use --all to remerge all files'))
 
-    t = opts.get('tool')
-    if t:
-        if 'HGMERGE' in os.environ:
-            os.environ['HGMERGE'] = ''
-        ui.setconfig('ui', 'merge', t)
-
     ms = mergemod.mergestate(repo)
     m = cmdutil.match(repo, pats, opts)
     ret = 0
@@ -3010,9 +3003,13 b' def resolve(ui, repo, *pats, **opts):'
                 a = repo.wjoin(f)
                 util.copyfile(a, a + ".resolve")
 
-                # resolve file
-                if ms.resolve(f, wctx, mctx):
-                    ret = 1
+                try:
+                    # resolve file
+                    ui.setconfig('ui', 'forcemerge', opts.get('tool', ''))
+                    if ms.resolve(f, wctx, mctx):
+                        ret = 1
+                finally:
+                    ui.setconfig('ui', 'forcemerge', '')
 
                 # replace filemerge's .orig file with our resolve file
                 util.rename(a + ".resolve", a + ".orig")

mercurial/filemerge.py

@@ -54,7 +54,17 b' def _picktool(repo, ui, path, binary, sy'
             return True
         return False
 
-    # HGMERGE takes precedence
+    # forcemerge comes from command line arguments, highest priority
+    force = ui.config('ui', 'forcemerge')
+    if force:
+        toolpath = _findtool(ui, force)
+        if toolpath:
+            return (force, '"' + toolpath + '"')
+        else:
+            # mimic HGMERGE if given tool not found
+            return (force, force)
+
+    # HGMERGE takes next precedence
     hgmerge = os.environ.get("HGMERGE")
     if hgmerge:
         return (hgmerge, hgmerge)

tests/test-merge-symlinks.t

@@ -37,7 +37,7 b' a file, once as a link. Bundle was gener'
 Merge them and display *_ISLINK vars
 merge heads
 
-  $ HGMERGE="python ../echo.py" hg merge
+  $ hg merge --tool="python ../echo.py"
   HG_FILE l
   HG_MY_ISLINK 1
   HG_OTHER_ISLINK 0

tests/test-merge-tools.t

@@ -506,6 +506,49 b' Premerge'
   $ echo
   
 
+ui.merge specifies internal:other but is overruled by --tool=false
+
+  $ domerge -r 2 --config ui.merge=internal:other --tool=false
+  [merge-tools]
+  false.whatever=
+  true.priority=1
+  true.executable=cat
+  # hg update -C 1
+  # hg merge -r 2 --config ui.merge=internal:other --tool=false
+  merging f
+  merging f failed!
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
+  # cat f
+  revision 1
+  space
+  # hg stat
+  M f
+  ? f.orig
+  
+HGMERGE specifies internal:other but is overruled by --tool=false
+
+  $ HGMERGE=internal:other ; export HGMERGE
+  $ domerge -r 2 --tool=false
+  [merge-tools]
+  false.whatever=
+  true.priority=1
+  true.executable=cat
+  # hg update -C 1
+  # hg merge -r 2 --tool=false
+  merging f
+  merging f failed!
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
+  # cat f
+  revision 1
+  space
+  # hg stat
+  M f
+  ? f.orig
+  
+  $ unset HGMERGE # make sure HGMERGE doesn't interfere with remaining tests
+
 Default is silent simplemerge:
 
   $ domerge -r 3

tests/test-rename-merge2.t

@@ -7,7 +7,6 b''
   > f.write("merge %s %s %s" % (sys.argv[1], sys.argv[2], sys.argv[3]))
   > f.close()
   > EOF
-  $ HGMERGE="python ../merge"; export HGMERGE
 
 perform a test merge with possible renaming
 args:
@@ -49,7 +48,7 b' args:'
   >     echo "--------------"
   >     echo "test L:$1 R:$2 W:$3 - $4"
   >     echo "--------------"
-  >     hg merge -y --debug --traceback
+  >     hg merge -y --debug --traceback --tool="python ../merge"
   > 
   >     echo "--------------"
   >     hg status -camC -X rev

tests/test-resolve.t

@@ -21,7 +21,7 b' create a second head'
 
 failing merge
 
-  $ HGMERGE=internal:fail hg merge
+  $ hg merge --tool=internal:fail
   0 files updated, 0 files merged, 0 files removed, 1 files unresolved
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
   [1]