qapi: Fix argument description indentation stripping

When an argument's description starts on the line after the "#arg: "
line, indentation is stripped only from the description's first line,
as demonstrated by the previous commit.  Moreover, subsequent lines
with less indentation are not rejected.

Make the first line's indentation the expected indentation for the
remainder of the description.  This fixes indentation stripping, and
also requires at least that much indentation.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230428105429.1687850-12-armbru@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>

scripts/qapi/parser.py

@@ -483,7 +483,9 @@ def append(self, line: str) -> None:
             # Blank lines are always OK.
             if line:
                 indent = must_match(r'\s*', line).end()
-                if indent < self._indent:
+                if self._indent < 0:
+                    self._indent = indent
+                elif indent < self._indent:
                     raise QAPIParseError(
                         self._parser,
                         "unexpected de-indent (expected at least %d spaces)" %
@@ -631,9 +633,9 @@ def _append_args_line(self, line: str) -> None:
             indent = must_match(r'@\S*:\s*', line).end()
             line = line[indent:]
             if not line:
-                # Line was just the "@arg:" header; following lines
-                # are not indented
-                indent = 0
+                # Line was just the "@arg:" header
+                # The next non-blank line determines expected indent
+                indent = -1
             else:
                 line = ' ' * indent + line
             self._start_args_section(name[1:-1], indent)
@@ -666,9 +668,9 @@ def _append_features_line(self, line: str) -> None:
             indent = must_match(r'@\S*:\s*', line).end()
             line = line[indent:]
             if not line:
-                # Line was just the "@arg:" header; following lines
-                # are not indented
-                indent = 0
+                # Line was just the "@arg:" header
+                # The next non-blank line determines expected indent
+                indent = -1
             else:
                 line = ' ' * indent + line
             self._start_features_section(name[1:-1], indent)
@@ -712,8 +714,8 @@ def _append_various_line(self, line: str) -> None:
             indent = must_match(r'\S*:\s*', line).end()
             line = line[indent:]
             if not line:
-                # Line was just the "Section:" header; following lines
-                # are not indented
+                # Line was just the "Section:" header
+                # The next non-blank line determines expected indent
                 indent = 0
             else:
                 line = ' ' * indent + line

tests/qapi-schema/doc-good.out

@@ -159,7 +159,7 @@ doc symbol=cmd
 
     arg=arg1
 description starts on a new line,
-    indented
+indented
     arg=arg2
 the second argument
     arg=arg3