Actually warn on pulling from an unrelated repository

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Actually warn on pulling from an unrelated repository

add some comments to findincoming
track the base nodes of the fetch set
report if the base set only contains nullid
add a test case

manifest hash: 3fc038a6041b0967a20503f5ec8876efc038841a
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tests/test-unrelated-pull

@@ -0,0 +1,17 b''
+mkdir a
+cd a
+hg init
+echo 123 > a
+hg add a
+hg commit -t "a" -u a -d "0 0"
+
+cd ..
+mkdir b
+cd b
+hg init 
+echo 321 > b
+hg add b
+hg commit -t "b" -u b -d "0 0"
+
+hg pull ../a
+hg heads

tests/test-unrelated-pull.out

@@ -0,0 +1,19 b''
+pulling from ../a
+searching for changes
+warning: pulling from an unrelated repository!
+adding changesets
+adding manifests
+adding file revisions
+modified 1 files, added 1 changesets and 1 new revisions
+(run 'hg update' to get a working copy)
+changeset:   1:9a79c33a9db37480e40fbd2a65d62ebd2a3c441c
+tag:         tip
+user:        a
+date:        Thu Jan  1 00:00:00 1970
+summary:     a
+
+changeset:   0:01f8062b2de51c0fa6428c5db1d1b3ea780189df
+user:        b
+date:        Thu Jan  1 00:00:00 1970
+summary:     b
+

mercurial/hg.py

@@ -852,6 +852,7 b' class localrepository:'
         m = self.changelog.nodemap
         search = []
         fetch = []
+        base = {}
         seen = {}
         seenbranch = {}
 
@@ -861,6 +862,7 b' class localrepository:'
             return [nullid]
 
         # otherwise, assume we're closer to the tip than the root
+        # and start by examining the heads
         self.ui.status("searching for changes\n")
         heads = remote.heads()
         unknown = []
@@ -874,6 +876,10 b' class localrepository:'
         rep = {}
         reqcnt = 0
 
+        # search through remote branches
+        # a 'branch' here is a linear segment of history, with four parts:
+        # head, root, first parent, second parent
+        # (a branch always has two parents (or none) by definition)
         unknown = remote.branches(unknown)
         while unknown:
             r = []
@@ -899,6 +905,7 b' class localrepository:'
                             self.ui.debug("found new changeset %s\n" %
                                           short(n[1]))
                             fetch.append(n[1]) # earliest unknown
+                            base[n[2]] = 1 # latest known
                             continue
 
                     for a in n[2:4]:
@@ -919,6 +926,7 b' class localrepository:'
                         if b[0] not in m and b[0] not in seen:
                             unknown.append(b)
 
+        # do binary search on the branches we found
         while search:
             n = search.pop(0)
             reqcnt += 1
@@ -933,6 +941,7 b' class localrepository:'
                         self.ui.debug("found new branch changeset %s\n" %
                                           short(p))
                         fetch.append(p)
+                        base[i] = 1
                     else:
                         self.ui.debug("narrowed branch search to %s:%s\n"
                                       % (short(p), short(i)))
@@ -940,11 +949,12 b' class localrepository:'
                     break
                 p, f = i, f * 2
 
+        # sanity check our fetch list
         for f in fetch:
             if f in m:
                 raise RepoError("already have changeset " + short(f[:4]))
 
-        if fetch == [nullid]:
+        if base.keys() == [nullid]:
             self.ui.warn("warning: pulling from an unrelated repository!\n")
 
         self.ui.note("adding new changesets starting at " +