Project item conflict diagnostics through enclosing scopes

internal/engine/imports.go

@@ -214,6 +214,9 @@ func loadImportedWithAccessTrackedAndProcessingPolicy(access *filesystemAccess,
 
 	closeErr := access.close()
 	if len(diagnostics) != 0 {
+		if mainIsItem {
+			diagnostics = prependCompositionDiagnosticPaths(diagnostics, destination.Index(0))
+		}
 		return nil, cloneSourceInfos(state.sources), diagnostics
 	}
 	if closeErr != nil {
@@ -227,7 +230,7 @@ func loadImportedWithAccessTrackedAndProcessingPolicy(access *filesystemAccess,
 		}
 		completed, failures := composeDocuments(documents...)
 		if len(failures) != 0 {
-			return nil, cloneSourceInfos(state.sources), prependDiagnosticPaths(failures, destination.Index(0))
+			return nil, cloneSourceInfos(state.sources), prependCompositionDiagnosticPaths(failures, destination.Index(0))
 		}
 		if versionState != nil {
 			protectionRule := versionState.localRule
@@ -525,7 +528,7 @@ func (s *importTraversal) visitItemSource(canonical string, declaration importDe
 	itemScope := s.scope
 	s.scope, s.itemScope, s.itemPrefix, s.itemFallback = parentScope, parentItemScope, parentPrefix, parentFallback
 	if len(diagnostics) != 0 {
-		return diagnostics
+		return projectItemDiagnosticPaths(diagnostics, parentScope, destination)
 	}
 	documents := make([]*document.Node, 0, len(itemScope.contributions))
 	for _, contribution := range itemScope.contributions {
@@ -533,11 +536,7 @@ func (s *importTraversal) visitItemSource(canonical string, declaration importDe
 	}
 	completed, diagnostics := composeDocuments(documents...)
 	if len(diagnostics) != 0 {
-		prefix := destination.Index(0)
-		if parentItemScope {
-			prefix = appendDestination(parentPrefix, prefix)
-		}
-		return prependDiagnosticPaths(diagnostics, prefix)
+		return projectItemDiagnosticPaths(diagnostics, parentScope, destination)
 	}
 	itemScope.destination = Path{}
 	completed.acquisition = []acquisitionScope{cloneAcquisitionScope(itemScope)}
@@ -580,9 +579,12 @@ func importedVersionClaim(documents []*document.Node, composed *composedDocument
 	return nil
 }
 
-func prependDiagnosticPaths(diagnostics []Diagnostic, prefix Path) []Diagnostic {
+func prependCompositionDiagnosticPaths(diagnostics []Diagnostic, prefix Path) []Diagnostic {
 	cloned := append([]Diagnostic(nil), diagnostics...)
 	for index := range cloned {
+		if !isCompositionDiagnostic(cloned[index]) {
+			continue
+		}
 		cloned[index].Path = appendDestination(prefix, cloned[index].Path)
 		cloned[index].Primary = cloneLocation(cloned[index].Primary)
 		cloned[index].Related = cloneLocations(cloned[index].Related)
@@ -590,6 +592,56 @@ func prependDiagnosticPaths(diagnostics []Diagnostic, prefix Path) []Diagnostic
 	return cloned
 }
 
+func isCompositionDiagnostic(diagnostic Diagnostic) bool {
+	return diagnostic.Code == CodeComposeConflict || diagnostic.Code == CodeComposeInvalid
+}
+
+// On a composition failure only the earlier contributions are needed to locate
+// this item. Project one enclosing scope at a time as traversal unwinds; syntax
+// and access diagnostics keep their original source-local coordinates.
+func projectItemDiagnosticPaths(diagnostics []Diagnostic, parent acquisitionScope, destination Path) []Diagnostic {
+	for _, diagnostic := range diagnostics {
+		if isCompositionDiagnostic(diagnostic) {
+			index := priorSequenceLength([]acquisitionScope{parent}, destination)
+			return prependCompositionDiagnosticPaths(diagnostics, destination.Index(index))
+		}
+	}
+	return diagnostics
+}
+
+// This scan is confined to failed loads, not the successful construction path.
+func priorSequenceLength(scopes []acquisitionScope, path Path) int {
+	length := 0
+	for _, scope := range scopes {
+		for _, contribution := range scope.contributions {
+			if node, present := documentAtPath(contribution.document, path); present && node.Kind == document.Sequence {
+				length += len(node.Sequence)
+			}
+		}
+	}
+	return length
+}
+
+func projectPriorInputDiagnosticPaths(diagnostics []Diagnostic, scopes []acquisitionScope) []Diagnostic {
+	cloned := cloneDiagnostics(diagnostics)
+	for index := range cloned {
+		if !isCompositionDiagnostic(cloned[index]) {
+			continue
+		}
+		for position, segment := range cloned[index].Path.segments {
+			if segment.kind != pathSegmentIndex {
+				continue
+			}
+			container := Path{segments: cloned[index].Path.segments[:position]}
+			cloned[index].Path.segments[position].index += priorSequenceLength(scopes, container)
+			// Registration does not address paths through item indexes. A prior
+			// input shifts the outer collection, not its item-local sequences.
+			break
+		}
+	}
+	return cloned
+}
+
 func projectNestedEvidence(composed *composedDocument, scope acquisitionScope) {
 	if composed == nil {
 		return

internal/engine/load_request.go

@@ -175,7 +175,7 @@ func acquireUnderlayGroupWithPolicyVersion(group loadGroup, index int, rule *Ver
 		}
 		mergeResourceContexts(&contexts, acquired.contexts)
 		if len(diagnostics) != 0 {
-			return nil, sources, contexts, diagnostics
+			return nil, sources, contexts, projectPriorInputDiagnosticPaths(diagnostics, scopes)
 		}
 		if acquired.document == nil {
 			continue