run-tests: support per-line conditional output in tests

Duplicating entire tests just because the output is different is both error
prone and can make the tests harder to read.  This harnesses the existing '(?)'
infrastructure, both to improve readability, and because it seemed like the path
of least resistance.

The form is:

  $ test_cmd
  output (hghave-feature !) # required if hghave.has_feature(), else optional
  out2 (no-hghave-feature2 !) # req if not hghave.has_feature2(), else optional

I originally extended the '(?)' syntax.  For example, this:

  2 r4/.hg/cache/checkisexec (execbit ?)

pretty naturally reads as "checkisexec, if execbit".  In some ways though, this
inverts the meaning of '?'.  For '(?)', the line is purely optional.  In the
example, it is mandatory iff execbit.  Otherwise, it is carried forward as
optional, to preserve the test output.  I tried it the other way, (listing
'no-exec' in the example), but that is too confusing to read.  Kostia suggested
using '!', and that seems fine.

tests/run-tests.py

@@ -497,6 +497,12 b' def vlog(*msg):'
 # sans \t, \n and \r
 CDATA_EVIL = re.compile(br"[\000-\010\013\014\016-\037]")
 
+# Match feature conditionalized output lines in the form, capturing the feature
+# list in group 2, and the preceeding line output in group 1:
+#
+#   output..output (feature !)\n
+optline = re.compile(b'(.+) \((.+?) !\)\n$')
+
 def cdatasafe(data):
     """Make a string safe to include in a CDATA block.
 
@@ -1271,8 +1277,19 b' class TTest(Test):'
                     if r:
                         els.pop(i)
                         break
-                    if el and el.endswith(b" (?)\n"):
-                        optional.append(i)
+                    if el:
+                        if el.endswith(b" (?)\n"):
+                            optional.append(i)
+                        else:
+                            m = optline.match(el)
+                            if m:
+                                conditions = [c for c in m.group(2).split(' ')]
+
+                                if self._hghave(conditions)[0]:
+                                    lout = el
+                                else:
+                                    optional.append(i)
+
                     i += 1
 
                 if r:
@@ -1298,8 +1315,10 b' class TTest(Test):'
                 # clean up any optional leftovers
                 while expected.get(pos, None):
                     el = expected[pos].pop(0)
-                    if el and not el.endswith(b" (?)\n"):
-                        break
+                    if el:
+                        if (not optline.match(el)
+                            and not el.endswith(b" (?)\n")):
+                            break
                     postout.append(b'  ' + el)
 
             if lcmd:
@@ -1371,6 +1390,12 b' class TTest(Test):'
             if el.endswith(b" (?)\n"):
                 retry = "retry"
                 el = el[:-5] + b"\n"
+            else:
+                m = optline.match(el)
+                if m:
+                    el = m.group(1) + b"\n"
+                    retry = "retry"
+
             if el.endswith(b" (esc)\n"):
                 if PYTHON3:
                     el = el[:-7].decode('unicode_escape') + '\n'

tests/test-run-tests.t

@@ -39,6 +39,19 b' error paths'
   $ rm hg
 #endif
 
+Features for testing optional lines
+===================================
+
+  $ cat > hghaveaddon.py <<EOF
+  > import hghave
+  > @hghave.check("custom", "custom hghave feature")
+  > def has_custom():
+  >     return True
+  > @hghave.check("missing", "missing hghave feature")
+  > def has_missing():
+  >     return False
+  > EOF
+
 an empty test
 =======================
 
@@ -67,6 +80,13 b' a succesful test'
   >   def (?)
   >   456 (?)
   >   xyz
+  >   $ printf 'zyx\nwvu\ntsr\n'
+  >   abc (?)
+  >   zyx (custom !)
+  >   wvu
+  >   no_print (no-custom !)
+  >   tsr (no-missing !)
+  >   missing (missing !)
   > EOF
 
   $ rt
@@ -341,6 +361,12 b' Running In Debug Mode'
   xyz
   + echo *SALT* 15 0 (glob)
   *SALT* 15 0 (glob)
+  + printf *zyx\nwvu\ntsr\n* (glob)
+  zyx
+  wvu
+  tsr
+  + echo *SALT* 22 0 (glob)
+  *SALT* 22 0 (glob)
   .
   # Ran 2 tests, 0 skipped, 0 warned, 0 failed.