[FIX] runbot_merge: EmailMessage.get_content misbehaves

`get_content` round-trips the text part through `ascii` with
`error=replace`, so if the input is not ascii it screws up
tremendously, which leads to either failing to apply patches (the more
likely situation) or corrupting the patches.

`get_payload`, if called without `decode`, pretty much just returns
the payload unless it needs a decoding pass (e.g. because it contains
raw surrogates, but that should not be an issue for us). So this is
really what we want.

While at it, increase `patch`'s verbosity in case it can give us more
info.

runbot_merge/models/patcher.py

@@ -99,7 +99,7 @@ def parse_format_patch(p: Patch) -> ParseResult:
     name, email = parseaddr(m['from'])
     author = (name, email, m['date'])
     msg = re.sub(r'^\[PATCH( \d+/\d+)?\] ', '', m['subject'])
-    body, _, rest = m.get_content().partition('---\n')
+    body, _, rest = m.get_payload().partition('---\n')
     if body:
         msg += '\n\n' + body
 
@@ -300,14 +300,14 @@ class Patch(models.Model):
              tempfile.TemporaryDirectory() as tmpdir:
             tf.extractall(tmpdir)
             patch = subprocess.run(
-                ['patch', f'-p{prefix}', '-d', tmpdir],
+                ['patch', f'-p{prefix}', '--directory', tmpdir, '--verbose'],
                 input=p.patch,
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
                 encoding='utf-8',
             )
             if patch.returncode:
-                raise PatchFailure(patch.stdout)
+                raise PatchFailure("\n---------\n".join(filter(None, [p.patch, patch.stdout.strip(), patch.stderr.strip()])))
             new_tree = r.update_tree(self.target.name, files)
 
         sha = r.stdout().with_config(encoding='utf-8')\

runbot_merge/tests/test_patching.py

@@ -2,7 +2,7 @@ import xmlrpc.client
 
 import pytest
 
-from utils import Commit, read_tracking_value
+from utils import Commit, read_tracking_value, matches
 
 # basic udiff / show style patch, updates `b` from `1` to `2`
 BASIC_UDIFF = """\
@@ -255,7 +255,7 @@ def test_patch_conflict(env, project, repo, users):
         [],
     ), (
         "Unable to apply patch",
-        "<p>patching file b<br>Hunk #1 FAILED at 1.<br>1 out of 1 hunk FAILED -- saving rejects to file b.rej<br></p>",
+        matches("$$"),  # feedback from patch can vary
         [],
     ), (
         False, '', [('active', 1, 0)]