fix(schema): make the container-location root fallback live

containerLocationMap stored `loc ?? rootLocation` into a [ObjectIdentifier:
String?]. Because the value type is itself optional the coalescing bound at the
outer optional and rootLocation was never used (the compiler flagged it), so a
container with no location of its own (the compile root) mapped to nil even when
a circular import had loaded the root under a schemaLocation. An explicit String?
annotation keeps the coalescing at the String level so the root inherits
rootLocation.

Conformance is unchanged: 1448 unit tests pass and the full XSTS suite still
settles at 0/43/0/31. The SchemaNameUniqueness root-index dedup case is kept, not
removed: an experiment removing it on the theory it was now redundant regressed
three valid schemas to rejected, so it does real work beyond the fixed fallback.

CHANGELOG.md

@@ -28,6 +28,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Fixed a dead `rootLocation` fallback in `XSDParser.containerLocationMap`. The
+  map value type is itself `String?`, so `loc ?? rootLocation` bound the
+  coalescing at the outer optional and never used `rootLocation` (the compiler
+  flagged it), leaving the compile root mapped to nil even when a circular import
+  had loaded it under a `schemaLocation`. An explicit `String?` annotation keeps
+  the coalescing at the `String` level so the root inherits its location.
+  Conformance is unchanged (XSTS still settles at 0/43/0/31); the
+  `SchemaNameUniqueness` root-index dedup case is retained, not removed, because
+  removing it on the theory it was now redundant regressed three valid schemas to
+  rejected, so it does real work beyond the fixed fallback.
+
 - Bounded the content-model matcher's active-configuration set per counter
   (`ContentNFA`/`ContentMatcher`). Each occurrence counter now saturates at
   `min(maximum, inputLength + 1)`, and an unbounded counter at its `minimum`

Sources/Schema/XSDParser.swift

@@ -64,7 +64,11 @@ extension PureXML.Schema.XSDParser {
     ) -> [ObjectIdentifier: String?] {
         var containerLocations: [ObjectIdentifier: String?] = [:]
         for (loc, tree) in containerTuples {
-            containerLocations[ObjectIdentifier(tree)] = loc ?? rootLocation
+            // The map value is itself `String?`, so the explicit annotation keeps
+            // `??` at the `String` level; without it the fallback binds at the
+            // outer optional and the compile root (no location) maps to nil.
+            let location: String? = loc ?? rootLocation
+            containerLocations[ObjectIdentifier(tree)] = location
         }
         return containerLocations
     }