tests: demonstrate broken manifest generation with the pure module stable

tests: demonstrate broken manifest generation with the pure module

This will be fixed next.  But I don't fully understand how 'b.txt' is actually
removed properly in the second test, given what's broken.  Also, I'm not sure
why 'bb.txt' is flagged as not being in the manifest, when it clearly appears
to be.

--- a/mercurial/manifest.py	Mon May 20 10:08:28 2019 +0200
+++ b/mercurial/manifest.py	Thu May 23 21:39:19 2019 -0400
@@ -35,6 +35,9 @@
 parsers = policy.importmod(r'parsers')
 propertycache = util.propertycache
 
+# Allow tests to more easily test the alternate path in manifestdict.fastdelta()
+FASTDELTA_TEXTDIFF_THRESHOLD = 1000
+
 def _parse(data):
     # This method does a little bit of excessive-looking
     # precondition checking. This is so that the behavior of this
@@ -558,7 +561,7 @@
         addbuf = util.buffer(base)
 
         changes = list(changes)
-        if len(changes) < 1000:
+        if len(changes) < FASTDELTA_TEXTDIFF_THRESHOLD:
             # start with a readonly loop that finds the offset of
             # each line and creates the deltas
             for f, todelete in changes:

--- a/tests/test-manifest.t	Mon May 20 10:08:28 2019 +0200
+++ b/tests/test-manifest.t	Thu May 23 21:39:19 2019 -0400
@@ -201,3 +201,94 @@
   total cache data size 425 bytes, on-disk 425 bytes
   $ hg log -r '0' --debug | grep 'manifest:'
   manifest:    0:fce2a30dedad1eef4da95ca1dc0004157aa527cf
+
+Test file removal (especially with pure).  The tests are crafted such that there
+will be contiguous spans of existing entries to ensure that is handled properly.
+(In this case, a.txt, aa.txt and c.txt, cc.txt, and ccc.txt)
+
+  $ cat > $TESTTMP/manifest.py <<EOF
+  > from mercurial import (
+  >     extensions,
+  >     manifest,
+  > )
+  > def extsetup(ui):
+  >     manifest.FASTDELTA_TEXTDIFF_THRESHOLD = 0
+  > EOF
+  $ cat >> $HGRCPATH <<EOF
+  > [extensions]
+  > manifest = $TESTTMP/manifest.py
+  > EOF
+
+BROKEN: Pure removes should actually remove all dropped entries
+
+  $ hg init repo
+  $ cd repo
+  $ echo a > a.txt
+  $ echo aa > aa.txt
+  $ echo b > b.txt
+  $ echo c > c.txt
+  $ echo c > cc.txt
+  $ echo c > ccc.txt
+  $ echo b > d.txt
+  $ echo c > e.txt
+  $ hg ci -Aqm 'a-e'
+
+  $ hg rm b.txt d.txt
+  $ hg ci -m 'remove b and d'
+
+  $ hg debugdata -m 1
+  a.txt\x00b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 (esc)
+  aa.txt\x00a4bdc161c8fbb523c9a60409603f8710ff49a571 (esc)
+  \x00.txt\x001e88685f5ddec574a34c70af492f95b6debc8741 (esc) (pure !)
+  c.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+  cc.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+  ccc.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+  \x00.txt\x001e88685f5ddec574a34c70af492f95b6debc8741 (esc) (pure !)
+  e.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+
+  $ hg up -C . 2>&1 | grep ValueError || true
+      raise ValueError("Manifest lines not in sorted order.") (pure !)
+  ValueError: Manifest lines not in sorted order. (pure !)
+
+  $ hg verify || true
+  checking changesets
+  checking manifests
+   manifest@1: reading delta c1f6b2f803ac: Non-hexadecimal digit found (pure !)
+  crosschecking files in changesets and manifests
+  checking files
+  checked 2 changesets with 8 changes to 8 files
+  1 integrity errors encountered! (pure !)
+  (first damaged changeset appears to be 1) (pure !)
+
+  $ hg rollback -q --config ui.rollback=True
+  $ hg rm b.txt d.txt
+  $ echo bb > bb.txt
+
+BROKEN: A mix of adds and removes should remove all dropped entries.
+
+  $ hg ci -Aqm 'remove b and d; add bb'
+
+  $ hg debugdata -m 1
+  a.txt\x00b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 (esc)
+  aa.txt\x00a4bdc161c8fbb523c9a60409603f8710ff49a571 (esc)
+  bb.txt\x0004c6faf8a9fdd848a5304dfc1704749a374dff44 (esc)
+  c.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+  cc.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+  ccc.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+  \x00.txt\x001e88685f5ddec574a34c70af492f95b6debc8741 (esc) (pure !)
+  e.txt\x00149da44f2a4e14f488b7bd4157945a9837408c00 (esc)
+
+  $ hg up -C . 2>&1 | grep ValueError || true
+      raise ValueError("Manifest lines not in sorted order.") (pure !)
+  ValueError: Manifest lines not in sorted order. (pure !)
+
+  $ hg verify || true
+  checking changesets
+  checking manifests
+   manifest@1: reading delta 0a0385480090: Manifest lines not in sorted order. (pure !)
+  crosschecking files in changesets and manifests
+   bb.txt@1: in changeset but not in manifest (pure !)
+  checking files
+  checked 2 changesets with 9 changes to 9 files
+  2 integrity errors encountered! (pure !)
+  (first damaged changeset appears to be 1) (pure !)