mformat: regenerate long lines even if they're already multiline

If kwargs_force_multiline is enabled, an ArgumentNode in a kwarg value can
already be marked multiline by the time we notice that the line needs to
be broken for length.  Ensure we still break the line in this case.

Fixes: #13512

mesonbuild/mformat.py

@@ -769,9 +769,8 @@ class ComputeLineLengths(FullAstVisitor):
     def split_if_needed(self, node: mparser.ArgumentNode) -> None:
         if len(node) and not node.is_multiline and self.length > self.config.max_line_length:
             arg = self.argument_stack[self.level] if len(self.argument_stack) > self.level else node
-            if not arg.is_multiline:
-                arg.is_multiline = True
-                self.need_regenerate = True
+            arg.is_multiline = True
+            self.need_regenerate = True
 
     def visit_ArgumentNode(self, node: mparser.ArgumentNode) -> None:
         self.argument_stack.append(node)

test cases/format/4 config/indentation.meson

@@ -71,3 +71,18 @@ if meson.project_version().version_compare('>1.2')
     endforeach
   endif
 endif
+
+subproject(
+  '@0@-@1@-@2@-@3@'.format(
+    meson.project_name(),
+    meson.project_version(),
+    meson.project_build_root(),
+    meson.project_source_root(),
+  ),
+  default_options : [
+    'aaaaaaaa=bbbbbbbbbb',
+    'cccccccccccc=ddddddddddddd',
+    'eeeeeeeeeeeeeee=fffffffffffff',
+    'gggggggggggggggggggggg=hhhhhhhhhhhhhhhhhhhh',
+  ],
+)