bugfix: Scopes shouldn't dynamically maintain include lists (#49494)

Fixes #49403.

When one scope included another, we were appending to a list stored on the scope to
track what was included, and we would clear the list when the scope was removed.

This assumes that the scopes are always strictly pushed then popped, but the order can
be violated when serializing config scopes across processes (and then activating
environments in subprocesses), or if, e.g., instead of removing each scope we simply
cleared the list of config scopes. Removal can be skipped, which can cause the list of
includes on a cached scope (like the one we use for environments) to grow every time it
is pushed, and this triggers an assertion error.

There isn't actually a need to construct and destroy the include list. We can just
compute it once and cache it -- it's the same every time.

- [x] Cache included scope list on scope objects
- [x] Do not dynamically append/clear the included scope list

Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>

lib/spack/spack/config.py

@@ -142,7 +142,23 @@ def __init__(self, name: str) -> None:
         self.sections = syaml.syaml_dict()
 
         #: names of any included scopes
-        self.included_scopes: List[str] = []
+        self._included_scopes: Optional[List["ConfigScope"]] = None
+
+    @property
+    def included_scopes(self) -> List["ConfigScope"]:
+        """Memoized list of included scopes, in the order they appear in this scope."""
+        if self._included_scopes is None:
+            self._included_scopes = []
+
+            includes = self.get_section("include")
+            if includes:
+                include_paths = [included_path(data) for data in includes["include"]]
+                for path in include_paths:
+                    included_scope = include_path_scope(path)
+                    if included_scope:
+                        self._included_scopes.append(included_scope)
+
+        return self._included_scopes
 
     def get_section_filename(self, section: str) -> str:
         raise NotImplementedError
@@ -460,36 +476,30 @@ def push_scope(
             scope: scope to be added
             priority: priority of the scope
         """
-        tty.debug(f"[CONFIGURATION: PUSH SCOPE]: {str(scope)}, priority={priority}", level=2)
-
         # TODO: As a follow on to #48784, change this to create a graph of the
         # TODO: includes AND ensure properly sorted such that the order included
         # TODO: at the highest level is reflected in the value of an option that
         # TODO: is set in multiple included files.
         # before pushing the scope itself, push any included scopes recursively, at same priority
-        includes = scope.get_section("include")
-        if includes:
-            include_paths = [included_path(data) for data in includes["include"]]
-            for path in reversed(include_paths):
-                included_scope = include_path_scope(path)
-                if not included_scope:
-                    continue
+        for included_scope in reversed(scope.included_scopes):
+            if _depth + 1 > MAX_RECURSIVE_INCLUDES:  # make sure we're not recursing endlessly
+                mark = ""
+                if hasattr(included_scope, "path") and syaml.marked(included_scope.path):
+                    mark = included_scope.path._start_mark  # type: ignore
+                raise RecursiveIncludeError(
+                    f"Maximum include recursion exceeded in {included_scope.name}", str(mark)
+                )
 
-                if _depth + 1 > MAX_RECURSIVE_INCLUDES:  # make sure we're not recursing endlessly
-                    mark = path.path._start_mark if syaml.marked(path.path) else ""  # type: ignore
-                    raise RecursiveIncludeError(
-                        f"Maximum include recursion exceeded in {path.path}", str(mark)
-                    )
-
-                # record this inclusion so that remove_scope() can use it
-                scope.included_scopes.append(included_scope.name)
-                self.push_scope(included_scope, priority=priority, _depth=_depth + 1)
+            # record this inclusion so that remove_scope() can use it
+            self.push_scope(included_scope, priority=priority, _depth=_depth + 1)
 
+        tty.debug(f"[CONFIGURATION: PUSH SCOPE]: {str(scope)}, priority={priority}", level=2)
         self.scopes.add(scope.name, value=scope, priority=priority)
 
     @_config_mutator
     def remove_scope(self, scope_name: str) -> Optional[ConfigScope]:
         """Removes a scope by name, and returns it. If the scope does not exist, returns None."""
+
         try:
             scope = self.scopes.remove(scope_name)
             tty.debug(f"[CONFIGURATION: REMOVE SCOPE]: {str(scope)}", level=2)
@@ -498,10 +508,11 @@ def remove_scope(self, scope_name: str) -> Optional[ConfigScope]:
             return None
 
         # transitively remove included scopes
-        for inc in scope.included_scopes:
-            assert inc in self.scopes, f"Included scope '{inc}' was never added to configuration!"
-            self.remove_scope(inc)
-        scope.included_scopes.clear()  # clean up includes for bookkeeping
+        for included_scope in scope.included_scopes:
+            assert (
+                included_scope.name in self.scopes
+            ), f"Included scope '{included_scope.name}' was never added to configuration!"
+            self.remove_scope(included_scope.name)
 
         return scope