Editorial: Do not use [[DFSAncestorIndex]] in InnerModuleLinking

nicolo-ribaudo · nicolo-ribaudo · commit ef3e71673ca6 · 2025-07-04T15:44:34.000+02:00
[[DFSAncestorIndex]] index is only set once per module during a given
traversal process, and it represents the module's index in _stack_.
Instead explicitly storing it, we can compute it given _stack_ when
needed (i.e. when we process an edge that "closes" a loop).
diff --git a/spec.html b/spec.html
@@ -27162,7 +27162,7 @@ <h1>
               </h1>
               <dl class="header">
                 <dt>description</dt>
-                <dd>It is used by Link to perform the actual linking process for _module_, as well as recursively on all other modules in the dependency graph. The _stack_ parameter, as well as a module's [[DFSAncestorIndex]] field, keep track of the depth-first search (DFS) traversal. In particular, [[DFSAncestorIndex]] is used to discover strongly connected components (SCCs), such that all modules in an SCC transition to ~linked~ together.</dd>
+                <dd>It is used by Link to perform the actual linking process for _module_, as well as recursively on all other modules in the dependency graph. The _stack_ parameter keeps track of the depth-first search (DFS) traversal and, together with the return value, it is used to discover strongly connected components (SCCs), such that all modules in an SCC transition to ~linked~ together.</dd>
               </dl>
 
               <emu-alg>
@@ -27174,12 +27174,11 @@ <h1>
                   1. Return _moduleIndex_.
                 1. If _module_.[[Status]] is ~linking~, then
                   1. Assert: _module_ occurs exactly once in _stack_.
-                  1. Assert: _module_.[[DFSAncestorIndex]] is not ~empty~.
-                  1. Return _module_.[[DFSAncestorIndex]].
+                  1. NOTE: Once a _module_ is added to _stack_, its index never changes. Implementations may thus cache _module_'s index when it's first inserted, rather than computing it here.
+                  1. Return the integer _i_ such that _stack_[_i_] = _module_.
                 1. Assert: _module_.[[Status]] is ~unlinked~.
                 1. Set _module_.[[Status]] to ~linking~.
                 1. Let _sccAncestorIndex_ be _moduleIndex_.
-                1. Set _module_.[[DFSAncestorIndex]] to _sccAncestorIndex_.
                 1. Append _module_ to _stack_.
                 1. For each ModuleRequest Record _request_ of _module_.[[RequestedModules]], do
                   1. Let _requiredModule_ be GetImportedModule(_module_, _request_).
