revset: add "matching" keyword

This keyword can be used to find revisions that "match" one or more fields of a
given set of revisions.

A revision matches another if all the selected fields (description, author,
branch, date, files, phase, parents, substate, user, summary and/or metadata)
match the corresponding values of those fields on the source revision.

By default this keyword looks for revisions that whose metadata match
(description, author and date) making it ideal to look for duplicate revisions.

matching takes 2 arguments (the second being optional):

1.- rev: a revset represeting a _single_ revision (e.g. tip, ., p1(.), etc)
2.- [field(s) to match]: an optional string containing the field or fields
(separated by spaces) to match.
    Valid fields are most regular context fields and some special fields:
    * regular fields:
      - description, author, branch, date, files, phase, parents,
      substate, user.
      Note that author and user are synonyms.
    * special fields: summary, metadata.
      - summary: matches the first line of the description.
      - metatadata: It is equivalent to matching 'description user date'
        (i.e. it matches the main metadata fields).

Examples:

1.- Look for revisions with the same metadata (author, description and date)
as the 11th revision:

hg log -r "matching(11)"

2.- Look for revisions with the same description as the 11th revision:

hg log -r "matching(11, description)"

3.- Look for revisions with the same 'summary' (i.e. same first line on their
description) as the 11th revision:

hg log -r "matching(11, summary)"

4.- Look for revisions with the same author as the current revision:

hg log -r "matching(., author)"

You could use 'user' rather than 'author' to get the same result.

5.- Look for revisions with the same description _AND_ author as the tip of the
repository:

hg log -r "matching(tip, 'author description')"

6.- Look for revisions touching the same files as the parent of the tip of the
repository

hg log -r "matching(p1(tip), files)"

7.- Look for revisions whose subrepos are on the same state as the tip of the
repository or its parent

hg log -r "matching(p1(tip):tip, substate)"

8.- Look for revisions whose author and subrepo states both match those of any
of the revisions on the stable branch:

hg log -r "matching(branch(stable), 'author substate')"

mercurial/revset.py

@@ -858,6 +858,84 b' def rev(repo, subset, x):'
         raise error.ParseError(_("rev expects a number"))
     return [r for r in subset if r == l]
 
+def matching(repo, subset, x):
+    """``matching(revision [, field])``
+    Changesets in which a given set of fields match the set of fields in the
+    selected revision or set.
+    To match more than one field pass the list of fields to match separated
+    by spaces (e.g. 'author description').
+    Valid fields are most regular revision fields and some special fields:
+    * regular fields:
+      - description, author, branch, date, files, phase, parents,
+      substate, user.
+      Note that author and user are synonyms.
+    * special fields: summary, metadata.
+      - summary: matches the first line of the description.
+      - metatadata: It is equivalent to matching 'description user date'
+        (i.e. it matches the main metadata fields).
+    metadata is the default field which is used when no fields are specified.
+    You can match more than one field at a time.
+    """
+    l = getargs(x, 1, 2, _("matching takes 1 or 2 arguments"))
+
+    revs = getset(repo, xrange(len(repo)), l[0])
+
+    fieldlist = ['metadata']
+    if len(l) > 1:
+            fieldlist = getstring(l[1],
+                _("matching requires a string "
+                "as its second argument")).split()
+
+    # Make sure that there are no repeated fields, and expand the
+    # 'special' 'metadata' field type
+    fields = []
+    for field in fieldlist:
+        if field == 'metadata':
+            fields += ['user', 'description', 'date']
+        else:
+            if field == 'author':
+                field = 'user'
+            fields.append(field)
+    fields = set(fields)
+
+    # We may want to match more than one field
+    # Each field will be matched with its own "getfield" function
+    # which will be added to the getfieldfuncs array of functions
+    getfieldfuncs = []
+    _funcs = {
+        'user': lambda r: repo[r].user(),
+        'branch': lambda r: repo[r].branch(),
+        'date': lambda r: repo[r].date(),
+        'description': lambda r: repo[r].description(),
+        'files': lambda r: repo[r].files(),
+        'parents': lambda r: repo[r].parents(),
+        'phase': lambda r: repo[r].phase(),
+        'substate': lambda r: repo[r].substate,
+        'summary': lambda r: repo[r].description().splitlines()[0],
+    }
+    for info in fields:
+        getfield = _funcs.get(info, None)
+        if getfield is None:
+            raise error.ParseError(
+                _("unexpected field name passed to matching: %s") % info)
+        getfieldfuncs.append(getfield)
+
+    # convert the getfield array of functions into a "getinfo" function
+    # which returns an array of field values (or a single value if there
+    # is only one field to match)
+    if len(getfieldfuncs) == 1:
+        getinfo = getfieldfuncs[0]
+    else:
+        getinfo = lambda r: [f(r) for f in getfieldfuncs]
+
+    matches = []
+    for rev in revs:
+        target = getinfo(rev)
+        matches += [r for r in subset if getinfo(r) == target]
+    if len(revs) > 1:
+        matches = sorted(set(matches))
+    return matches
+
 def reverse(repo, subset, x):
     """``reverse(set)``
     Reverse order of set.
@@ -1019,6 +1097,7 b' symbols = {'
     "roots": roots,
     "sort": sort,
     "secret": secret,
+    "matching": matching,
     "tag": tag,
     "tagged": tagged,
     "user": user,