# HG changeset patch
# User Anton Shestakov <av6@dwimlabs.net>
# Date 1671109645 -14400
# Node ID e8d85d51c7b2efad48b6a8f1e23bd1a023516854
# Parent  f168c0fdbde9bd9f9c30b85d94f865371a807fd8
topic: monkey-patch ctx.branch() correctly in override_context_branch

There's a `for p in ctx.parents()` loop in this block of code, and it's used to
monkey-patch .branch() method for both parents of ctx. It assigns each parent
of ctx to variable `p` (implicitly) and p.branch method to variable `pbranch`
(explicitly).

This worked fine when there's only one p1, but when there were 2 parents, this
code was broken, and our tests didn't catch this because the use of
override_context_branch context manager is quite limited.

The problem is that the newly created function uses `p` and `pbranch`, and the
closures for the new p1.branch() and p2.branch() didn't get created until the
for-loop finished, and the values `p` and `pbranch` could change before that.
In other words, the new .branch method of p1 was effectively identical to p2's
because the values that were available to it were from the second cycle of the
for-loop, when it the loop was at p2.

Now we pass the values to a function that creates the new .branch methods, and
since these values are provided to overridebranch() as arguments, they get
enclosed when the function returns.

This was seen (and tested) during topic namespaces-related work, when
override_context_branch usage was expanded to include some local operations.

diff -r f168c0fdbde9 -r e8d85d51c7b2 hgext3rd/topic/discovery.py
--- a/hgext3rd/topic/discovery.py	Tue Dec 13 20:03:23 2022 +0400
+++ b/hgext3rd/topic/discovery.py	Thu Dec 15 17:07:25 2022 +0400
@@ -25,6 +25,17 @@
 def override_context_branch(repo, publishedset=()):
     unfi = repo.unfiltered()
 
+    def overridebranch(p, origbranch):
+        def branch():
+            b = origbranch()
+            if p.rev() in publishedset:
+                return b
+            t = p.topic()
+            if t:
+                b = b"%s:%s" % (b, t)
+            return b
+        return branch
+
     class repocls(unfi.__class__):
         # awful hack to see branch as "branch:topic"
         def __getitem__(self, key):
@@ -47,17 +58,8 @@
                 for p in parents:
                     if getattr(p, '_topic_ext_branch_hack', False):
                         continue
-                    pbranch = p.branch
 
-                    def branch():
-                        branch = pbranch()
-                        if p.rev() in publishedset:
-                            return branch
-                        topic = p.topic()
-                        if topic:
-                            branch = b"%s:%s" % (branch, topic)
-                        return branch
-                    p.branch = branch
+                    p.branch = overridebranch(p, p.branch)
                     p._topic_ext_branch_hack = True
                 return parents