drawdag: update test repos by drawing the changelog DAG in ASCII

Currently, we have "debugbuilddag" which is a powerful tool to build test
cases but not intuitive. We may end up running "hg log" in the test to make
the test more readable.

This patch adds a "drawdag" extension with a "debugdrawdag" command for
similar testing purpose. Unlike the cryptic "debugbuilddag" command, it
reads an ASCII graph that is intuitive to human, so the test case can be
more readable.

Unlike "debugbuilddag", "drawdag" does not require an empty repo. So it can
be used to add new changesets to an existing repo.

Since the "drawdag" logic is not that trivial and only makes sense for
testing purpose, the extension is added to the "tests" directory, to make
the core logic clean. If we find it useful (for example, to demonstrate
cases and help user understand some cases) and want to ship it by default in
the future, we can move it to a ship-by-default "debugdrawdag" at that time.

tests/drawdag.py

@@ -0,0 +1,311 b''
+# drawdag.py - convert ASCII revision DAG to actual changesets
+#
+# Copyright 2016 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""
+create changesets from an ASCII graph for testing purpose.
+
+For example, given the following input::
+
+    c d
+    |/
+    b
+    |
+    a
+
+4 changesets and 4 local tags will be created.
+`hg log -G -T "{rev} {desc} (tag: {tags})"` will output::
+
+    o  3 d (tag: d tip)
+    |
+    | o  2 c (tag: c)
+    |/
+    o  1 b (tag: b)
+    |
+    o  0 a (tag: a)
+
+For root nodes (nodes without parents) in the graph, they can be revsets
+pointing to existing nodes.  The ASCII graph could also have disconnected
+components with same names referring to the same changeset.
+
+Therefore, given the repo having the 4 changesets (and tags) above, with the
+following ASCII graph as input::
+
+    foo    bar       bar  foo
+     |     /          |    |
+    ancestor(c,d)     a   baz
+
+The result (`hg log -G -T "{desc}"`) will look like::
+
+    o    foo
+    |\
+    +---o  bar
+    | | |
+    | o |  baz
+    |  /
+    +---o  d
+    | |
+    +---o  c
+    | |
+    o |  b
+    |/
+    o  a
+
+Note that if you take the above `hg log` output directly as input. It will work
+as expected - the result would be an isomorphic graph::
+
+    o    foo
+    |\
+    | | o  d
+    | |/
+    | | o  c
+    | |/
+    | | o  bar
+    | |/|
+    | o |  b
+    | |/
+    o /  baz
+     /
+    o  a
+
+This is because 'o' is specially handled in the input: instead of using 'o' as
+the node name, the word to the right will be used.
+"""
+from __future__ import absolute_import, print_function
+
+import collections
+import itertools
+
+from mercurial.i18n import _
+from mercurial import (
+    cmdutil,
+    context,
+    error,
+    node,
+    scmutil,
+)
+
+cmdtable = {}
+command = cmdutil.command(cmdtable)
+
+_pipechars = '\\/+-|'
+_nonpipechars = ''.join(chr(i) for i in xrange(33, 127)
+                        if chr(i) not in _pipechars)
+
+def _isname(ch):
+    """char -> bool. return True if ch looks like part of a name, False
+    otherwise"""
+    return ch in _nonpipechars
+
+def _parseasciigraph(text):
+    """str -> {str : [str]}. convert the ASCII graph to edges"""
+    lines = text.splitlines()
+    edges = collections.defaultdict(list)  # {node: []}
+
+    def get(y, x):
+        """(int, int) -> char. give a coordinate, return the char. return a
+        space for anything out of range"""
+        if x < 0 or y < 0:
+            return ' '
+        try:
+            return lines[y][x]
+        except IndexError:
+            return ' '
+
+    def getname(y, x):
+        """(int, int) -> str. like get(y, x) but concatenate left and right
+        parts. if name is an 'o', try to replace it to the right"""
+        result = ''
+        for i in itertools.count(0):
+            ch = get(y, x - i)
+            if not _isname(ch):
+                break
+            result = ch + result
+        for i in itertools.count(1):
+            ch = get(y, x + i)
+            if not _isname(ch):
+                break
+            result += ch
+        if result == 'o':
+            # special handling, find the name to the right
+            result = ''
+            for i in itertools.count(2):
+                ch = get(y, x + i)
+                if ch == ' ' or ch in _pipechars:
+                    if result or x + i >= len(lines[y]):
+                        break
+                else:
+                    result += ch
+            return result or 'o'
+        return result
+
+    def parents(y, x):
+        """(int, int) -> [str]. follow the ASCII edges at given position,
+        return a list of parents"""
+        visited = set([(y, x)])
+        visit = []
+        result = []
+
+        def follow(y, x, expected):
+            """conditionally append (y, x) to visit array, if it's a char
+            in excepted. 'o' in expected means an '_isname' test.
+            if '-' (or '+') is not in excepted, and get(y, x) is '-' (or '+'),
+            the next line (y + 1, x) will be checked instead."""
+            ch = get(y, x)
+            if any(ch == c and c not in expected for c in '-+'):
+                y += 1
+                return follow(y + 1, x, expected)
+            if ch in expected or ('o' in expected and _isname(ch)):
+                visit.append((y, x))
+
+        #  -o-  # starting point:
+        #  /|\ # follow '-' (horizontally), and '/|\' (to the bottom)
+        follow(y + 1, x, '|')
+        follow(y + 1, x - 1, '/')
+        follow(y + 1, x + 1, '\\')
+        follow(y, x - 1, '-')
+        follow(y, x + 1, '-')
+
+        while visit:
+            y, x = visit.pop()
+            if (y, x) in visited:
+                continue
+            visited.add((y, x))
+            ch = get(y, x)
+            if _isname(ch):
+                result.append(getname(y, x))
+                continue
+            elif ch == '|':
+                follow(y + 1, x, '/|o')
+                follow(y + 1, x - 1, '/')
+                follow(y + 1, x + 1, '\\')
+            elif ch == '+':
+                follow(y, x - 1, '-')
+                follow(y, x + 1, '-')
+                follow(y + 1, x - 1, '/')
+                follow(y + 1, x + 1, '\\')
+                follow(y + 1, x, '|')
+            elif ch == '\\':
+                follow(y + 1, x + 1, '\\|o')
+            elif ch == '/':
+                follow(y + 1, x - 1, '/|o')
+            elif ch == '-':
+                follow(y, x - 1, '-+o')
+                follow(y, x + 1, '-+o')
+        return result
+
+    for y, line in enumerate(lines):
+        for x, ch in enumerate(line):
+            if ch == '#':  # comment
+                break
+            if _isname(ch):
+                edges[getname(y, x)] += parents(y, x)
+
+    return dict(edges)
+
+class simplefilectx(object):
+    def __init__(self, path, data):
+        self._data = data
+        self._path = path
+
+    def data(self):
+        return self._data
+
+    def path(self):
+        return self._path
+
+    def renamed(self):
+        return None
+
+    def flags(self):
+        return ''
+
+class simplecommitctx(context.committablectx):
+    def __init__(self, repo, name, parentctxs, added=None):
+        opts = {
+            'changes': scmutil.status([], added or [], [], [], [], [], []),
+            'date': '0 0',
+            'extra': {'branch': 'default'},
+        }
+        super(simplecommitctx, self).__init__(self, name, **opts)
+        self._repo = repo
+        self._name = name
+        self._parents = parentctxs
+        self._parents.sort(key=lambda c: c.node())
+        while len(self._parents) < 2:
+            self._parents.append(repo[node.nullid])
+
+    def filectx(self, key):
+        return simplefilectx(key, self._name)
+
+    def commit(self):
+        return self._repo.commitctx(self)
+
+def _walkgraph(edges):
+    """yield node, parents in topologically order"""
+    visible = set(edges.keys())
+    remaining = {}  # {str: [str]}
+    for k, vs in edges.iteritems():
+        for v in vs:
+            if v not in remaining:
+                remaining[v] = []
+        remaining[k] = vs[:]
+    while remaining:
+        leafs = [k for k, v in remaining.items() if not v]
+        if not leafs:
+            raise error.Abort(_('the graph has cycles'))
+        for leaf in sorted(leafs):
+            if leaf in visible:
+                yield leaf, edges[leaf]
+            del remaining[leaf]
+            for k, v in remaining.iteritems():
+                if leaf in v:
+                    v.remove(leaf)
+
+@command('debugdrawdag', [])
+def debugdrawdag(ui, repo, **opts):
+    """read an ASCII graph from stdin and create changesets
+
+    The ASCII graph is like what :hg:`log -G` outputs, with each `o` replaced
+    to the name of the node. The command will create dummy changesets and local
+    tags with those names to make the dummy changesets easier to be referred
+    to.
+
+    If the name of a node is a single character 'o', It will be replaced by the
+    word to the right. This makes it easier to reuse
+    :hg:`log -G -T '{desc}'` outputs.
+
+    For root (no parents) nodes, revset can be used to query existing repo.
+    Note that the revset cannot have confusing characters which can be seen as
+    the part of the graph edges, like `|/+-\`.
+    """
+    text = ui.fin.read()
+
+    # parse the graph and make sure len(parents) <= 2 for each node
+    edges = _parseasciigraph(text)
+    for k, v in edges.iteritems():
+        if len(v) > 2:
+            raise error.Abort(_('%s: too many parents: %s')
+                              % (k, ' '.join(v)))
+
+    committed = {None: node.nullid}  # {name: node}
+
+    # for leaf nodes, try to find existing nodes in repo
+    for name, parents in edges.iteritems():
+        if len(parents) == 0:
+            try:
+                committed[name] = scmutil.revsingle(repo, name)
+            except error.RepoLookupError:
+                pass
+
+    # commit in topological order
+    for name, parents in _walkgraph(edges):
+        if name in committed:
+            continue
+        pctxs = [repo[committed[n]] for n in parents]
+        ctx = simplecommitctx(repo, name, pctxs, [name])
+        n = ctx.commit()
+        committed[name] = n
+        repo.tag(name, n, message=None, user=None, date=None, local=True)