branchmap: add a test that shows bad interaction with strip

Differential Revision: https://phab.mercurial-scm.org/D12549

tests/test-strip-branch-cache.t

@@ -0,0 +1,56 b''
+Define helpers.
+
+  $ hg_log () { hg log -G -T "{rev}:{node|short}"; }
+  $ commit () { echo "foo - ${2:-$1}" > $1; hg commit -Aqm "Edited $1"; }
+  $ strip() { hg --config extensions.strip= strip -q -r "$1" ; }
+
+Setup hg repo.
+
+  $ hg init repo
+  $ cd repo
+  $ touch x; hg add x; hg commit -m "initial"
+  $ hg clone -q . ../clone
+  $ commit a
+
+  $ cd ../clone
+
+  $ commit b
+
+  $ hg pull -q ../repo
+
+  $ cat .hg/cache/branch2-visible
+  222ae9789a75703f9836e44de7db179cbfd420ee 2
+  a3498d6e39376d2456425dd8c692367bdbf00fa2 o default
+  222ae9789a75703f9836e44de7db179cbfd420ee o default
+
+  $ hg_log
+  o  2:222ae9789a75
+  |
+  | @  1:a3498d6e3937
+  |/
+  o  0:7ab0a3bd758a
+  
+
+  $ strip '1:'
+
+The branchmap cache is not adjusted on strip.
+Now mentions a changelog entry that has been stripped.
+
+  $ cat .hg/cache/branch2-visible
+  222ae9789a75703f9836e44de7db179cbfd420ee 2
+  a3498d6e39376d2456425dd8c692367bdbf00fa2 o default
+  222ae9789a75703f9836e44de7db179cbfd420ee o default
+
+  $ commit c
+
+Not adjusted on commit, either.
+
+  $ cat .hg/cache/branch2-visible
+  222ae9789a75703f9836e44de7db179cbfd420ee 2
+  a3498d6e39376d2456425dd8c692367bdbf00fa2 o default
+  222ae9789a75703f9836e44de7db179cbfd420ee o default
+
+On pull we end up with the same tip, and so wrongly reuse the invalid cache and crash.
+
+  $ hg pull ../repo 2>&1 | grep 'ValueError:'
+  ValueError: node a3498d6e39376d2456425dd8c692367bdbf00fa2 does not exist (known-bad-output !)