diff hgext/show.py @ 34191:e6b5e7329ff2

show: use consistent (and possibly shorter) node lengths

`hg show` makes heavy use of shortest() to limit the length of the node
hash.

For the "stack" and "work" views, you are often looking at multiple
lines of similar output for "lines" of work. It is visually appeasing
for things to vertically align. A naive use of {shortest(node, N)}
could result in variable length nodes and for the first character of
the description to vary by a column or two.

We implement a function to determine the longest shortest prefix for
a set of revisions. The new function is used to determine the printed
node length for all `hg show` views.

.. feature::

   show: use consistent node length in views

Our previous shortest node length of 5 was arbitrarily chosen.

shortest() already does the work of ensuring that a partial node
isn't ambiguous with an integer revision, which is our primary risk
of a collision for very short nodes. It should be safe to go with the
shortest node possible.

Existing code is also optimized to handle nodes as short as 4.

So, we decrease the minimum hash length from 5 to 4.

We also add a test demonstrating that prefix collisions increase the
node length.

.. feature::

   show: decrease minimum displayed hash length from 5 to 4

Differential Revision: https://phab.mercurial-scm.org/D558

--- a/hgext/show.py	Thu Aug 03 21:51:34 2017 -0700
+++ b/hgext/show.py	Wed Sep 13 21:15:46 2017 -0700
@@ -161,9 +161,10 @@
             ui.write(_('(no bookmarks set)\n'))
         return
 
+    revs = [repo[node].rev() for node in marks.values()]
     active = repo._activebookmark
     longestname = max(len(b) for b in marks)
-    # TODO consider exposing longest shortest(node).
+    nodelen = longestshortest(repo, revs)
 
     for bm, node in sorted(marks.items()):
         fm.startitem()
@@ -172,7 +173,7 @@
         fm.write('node', fm.hexfunc(node), fm.hexfunc(node))
         fm.data(active=bm == active,
                 longestbookmarklen=longestname,
-                nodelen=5)
+                nodelen=nodelen)
 
 @showview('stack', csettopic='stack')
 def showstack(ui, repo, displayer):
@@ -236,6 +237,9 @@
     else:
         newheads = set()
 
+    allrevs = set(stackrevs) | newheads | set([baserev])
+    nodelen = longestshortest(repo, allrevs)
+
     try:
         cmdutil.findcmd('rebase', commands.table)
         haverebase = True
@@ -247,7 +251,7 @@
     # our simplicity and the customizations required.
     # TODO use proper graph symbols from graphmod
 
-    shortesttmpl = formatter.maketemplater(ui, '{shortest(node, 5)}')
+    shortesttmpl = formatter.maketemplater(ui, '{shortest(node, %d)}' % nodelen)
     def shortest(ctx):
         return shortesttmpl.render({'ctx': ctx, 'node': ctx.hex()})
 
@@ -278,7 +282,7 @@
                 ui.write('  ')
 
             ui.write(('o  '))
-            displayer.show(ctx, nodelen=5)
+            displayer.show(ctx, nodelen=nodelen)
             displayer.flush(ctx)
             ui.write('\n')
 
@@ -318,7 +322,7 @@
             ui.write('  ')
 
         ui.write(symbol, '  ')
-        displayer.show(ctx, nodelen=5)
+        displayer.show(ctx, nodelen=nodelen)
         displayer.flush(ctx)
         ui.write('\n')
 
@@ -335,7 +339,7 @@
         ui.write(_('(stack base)'), '\n', label='stack.label')
         ui.write(('o  '))
 
-        displayer.show(basectx, nodelen=5)
+        displayer.show(basectx, nodelen=nodelen)
         displayer.flush(basectx)
         ui.write('\n')
 
@@ -394,12 +398,13 @@
     """changesets that aren't finished"""
     # TODO support date-based limiting when calling revset.
     revs = repo.revs('sort(_underway(), topo)')
+    nodelen = longestshortest(repo, revs)
 
     revdag = graphmod.dagwalker(repo, revs)
 
     ui.setconfig('experimental', 'graphshorten', True)
     cmdutil.displaygraph(ui, repo, revdag, displayer, graphmod.asciiedges,
-                         props={'nodelen': 5})
+                         props={'nodelen': nodelen})
 
 def extsetup(ui):
     # Alias `hg <prefix><view>` to `hg show <view>`.
@@ -420,6 +425,27 @@
 
             ui.setconfig('alias', name, 'show %s' % view, source='show')
 
+def longestshortest(repo, revs, minlen=4):
+    """Return the length of the longest shortest node to identify revisions.
+
+    The result of this function can be used with the ``shortest()`` template
+    function to ensure that a value is unique and unambiguous for a given
+    set of nodes.
+
+    The number of revisions in the repo is taken into account to prevent
+    a numeric node prefix from conflicting with an integer revision number.
+    If we fail to do this, a value of e.g. ``10023`` could mean either
+    revision 10023 or node ``10023abc...``.
+    """
+    tmpl = formatter.maketemplater(repo.ui, '{shortest(node, %d)}' % minlen)
+    lens = [minlen]
+    for rev in revs:
+        ctx = repo[rev]
+        shortest = tmpl.render({'ctx': ctx, 'node': ctx.hex()})
+        lens.append(len(shortest))
+
+    return max(lens)
+
 # Adjust the docstring of the show command so it shows all registered views.
 # This is a bit hacky because it runs at the end of module load. When moved
 # into core or when another extension wants to provide a view, we'll need