[PATCH v2 09/21] qapi: add must_match helper

[John Snow <jsnow@redhat.com>]

Mypy cannot generally understand that these regex functions cannot
possibly fail. Add a "must_match" helper that makes this clear for
mypy.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/common.py |  8 +++++++-
 scripts/qapi/main.py   |  6 ++----
 scripts/qapi/parser.py | 13 +++++++------
 3 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
index cbd3fd81d36..6ad1eeb61d4 100644
--- a/scripts/qapi/common.py
+++ b/scripts/qapi/common.py
@@ -12,7 +12,7 @@
 # See the COPYING file in the top-level directory.
 
 import re
-from typing import Optional, Sequence
+from typing import Match, Optional, Sequence
 
 
 #: Magic string that gets removed along with all space to its right.
@@ -210,3 +210,9 @@ def gen_endif(ifcond: Sequence[str]) -> str:
 #endif /* %(cond)s */
 ''', cond=ifc)
     return ret
+
+
+def must_match(pattern: str, string: str) -> Match[str]:
+    match = re.match(pattern, string)
+    assert match is not None
+    return match
diff --git a/scripts/qapi/main.py b/scripts/qapi/main.py
index 703e7ed1ed5..f2ea6e0ce4a 100644
--- a/scripts/qapi/main.py
+++ b/scripts/qapi/main.py
@@ -8,11 +8,11 @@
 """
 
 import argparse
-import re
 import sys
 from typing import Optional
 
 from .commands import gen_commands
+from .common import must_match
 from .error import QAPIError
 from .events import gen_events
 from .introspect import gen_introspect
@@ -22,9 +22,7 @@
 
 
 def invalid_prefix_char(prefix: str) -> Optional[str]:
-    match = re.match(r'([A-Za-z_.-][A-Za-z0-9_.-]*)?', prefix)
-    # match cannot be None, but mypy cannot infer that.
-    assert match is not None
+    match = must_match(r'([A-Za-z_.-][A-Za-z0-9_.-]*)?', prefix)
     if match.end() != len(prefix):
         return prefix[match.end()]
     return None
diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
index 5ef1b8935e6..39de24785ac 100644
--- a/scripts/qapi/parser.py
+++ b/scripts/qapi/parser.py
@@ -18,6 +18,7 @@
 import os
 import re
 
+from .common import must_match
 from .error import QAPISemError, QAPISourceError
 from .source import QAPISourceInfo
 
@@ -238,8 +239,8 @@ def accept(self, skip_comment=True):
             elif not self.tok.isspace():
                 # Show up to next structural, whitespace or quote
                 # character
-                match = re.match('[^[\\]{}:,\\s\'"]+',
-                                 self.src[self.cursor-1:])
+                match = must_match('[^[\\]{}:,\\s\'"]+',
+                                   self.src[self.cursor-1:])
                 raise QAPIParseError(self, "stray '%s'" % match.group(0))
 
     def get_members(self):
@@ -369,7 +370,7 @@ def append(self, line):
             # Strip leading spaces corresponding to the expected indent level
             # Blank lines are always OK.
             if line:
-                indent = re.match(r'\s*', line).end()
+                indent = must_match(r'\s*', line).end()
                 if indent < self._indent:
                     raise QAPIParseError(
                         self._parser,
@@ -505,7 +506,7 @@ def _append_args_line(self, line):
             # from line and replace it with spaces so that 'f' has the
             # same index as it did in the original line and can be
             # handled the same way we will handle following lines.
-            indent = re.match(r'@\S*:\s*', line).end()
+            indent = must_match(r'@\S*:\s*', line).end()
             line = line[indent:]
             if not line:
                 # Line was just the "@arg:" header; following lines
@@ -540,7 +541,7 @@ def _append_features_line(self, line):
             # from line and replace it with spaces so that 'f' has the
             # same index as it did in the original line and can be
             # handled the same way we will handle following lines.
-            indent = re.match(r'@\S*:\s*', line).end()
+            indent = must_match(r'@\S*:\s*', line).end()
             line = line[indent:]
             if not line:
                 # Line was just the "@arg:" header; following lines
@@ -586,7 +587,7 @@ def _append_various_line(self, line):
             # from line and replace it with spaces so that 'f' has the
             # same index as it did in the original line and can be
             # handled the same way we will handle following lines.
-            indent = re.match(r'\S*:\s*', line).end()
+            indent = must_match(r'\S*:\s*', line).end()
             line = line[indent:]
             if not line:
                 # Line was just the "Section:" header; following lines
-- 
2.30.2