Reapply #2639 (with fix for #2680)

[trevor-scheer]

This PR ports #2684 to the 2.5.x release line.

This commit reapplies #2639 with an additional fix related to reproducing and resolving #2680.

The bug existed in the SelectionSet.contains logic in the final check to provide a ContainsResult. Here the lengths of the compared selection sets are used to determine subset or strictly equal. In the case that the __typename field was ignored up above, the comparison becomes invalid unless we offset the comparison by 1 to account for the non-existent field.

[changeset-bot]

🦋 Changeset detected

Latest commit: c6eddfa

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@apollo/query-planner	Patch
@apollo/federation-internals	Patch
@apollo/gateway	Patch
@apollo/composition	Patch
@apollo/query-graphs	Patch
@apollo/subgraph	Patch
apollo-federation-integration-testsuite	Patch

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[glasser]

This part is the fix, right?

@@ -1856,8 +1856,12 @@ export class SelectionSet {
     }
 
     let isEqual = true;
+    let didIgnoreTypename = false;
     for (const [key, thatSelection] of that._keyedSelections) {
       if (key === typenameFieldName && ignoreMissingTypename) {
+        if (!this._keyedSelections.has(typenameFieldName)) {
+          didIgnoreTypename = true;
+        }
         continue;
       }
 
@@ -1869,7 +1873,7 @@ export class SelectionSet {
       isEqual &&= selectionResult === ContainsResult.EQUAL;
     }
 
-    return isEqual && that._selections.length === this._selections.length
+    return isEqual && that._selections.length === (this._selections.length + (didIgnoreTypename ? 1 : 0))
       ? ContainsResult.EQUAL
       : ContainsResult.STRICTLY_CONTAINED;
   }

[trevor-scheer]

@glasser correct

[glasser]

oh that's more obvious in the non-backport :)