Share indexed fallback locations during effective projection

docs/roadmap/remediation.md

@@ -887,7 +887,14 @@ do not replace the agreed scheduling algorithm or add global caches.
 
 ## 22. Index Fallback Location Lookup During Effective Projection — P2
 
-Status: [ ] Open.
+Status: [x] Complete.
+
+Completion: effective location projection lazily builds one read-only fallback
+document lookup and shares it across field and entry visits. The ordinary
+nearest-location helper retains its existing behavior. Added broad mixed
+authored/default mappings, ancestor fallback, literal key/index mismatch,
+synthetic CLI coordinates, and detached-projection coverage. Existing secret
+and validation diagnostics and `./scripts/check.sh` pass.
 
 Owner: `documentWithMetadataLocations` in
 [`override_context.go`](../../internal/engine/override_context.go), using

internal/engine/metadata_locations_test.go

@@ -0,0 +1,79 @@
+package engine
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+func TestMetadataLocationsAcrossBroadAuthoredAndDefaultMappings(t *testing.T) {
+	type config map[string]map[string]string
+	defaults := config{}
+	var body strings.Builder
+	for index := range 96 {
+		name := fmt.Sprintf("authored-%03d", index)
+		fmt.Fprintf(&body, "%s: {present: source}\n", name)
+		defaults[name] = map[string]string{"absent": "default"}
+		defaults[fmt.Sprintf("default-%03d", index)] = map[string]string{"absent": "default"}
+	}
+	input := parseDocumentForDecode(t, body.String())
+	decoded, issues := decodeConfiguration(mustSchemaFor[config](t), reflect.ValueOf(defaults), input)
+	if len(issues) != 0 {
+		t.Fatal(issues)
+	}
+	located := documentWithMetadataLocations(decoded.final, metadataFromDecoded(decoded), input)
+	inputIndex := buildDocumentLookup(input)
+	locatedIndex := buildDocumentLookup(located)
+	for index := range 96 {
+		authored := Keys(fmt.Sprintf("authored-%03d", index))
+		mapping, _ := documentAtPathWithLookup(input, authored, inputIndex)
+		present, _ := documentAtPathWithLookup(input, authored.Key("present"), inputIndex)
+		for _, test := range []struct {
+			path Path
+			want document.Location
+		}{
+			{authored.Key("present"), present.Location},
+			{authored.Key("absent"), mapping.Location},
+			{Keys(fmt.Sprintf("default-%03d", index), "absent"), input.Location},
+		} {
+			node, found := documentAtPathWithLookup(located, test.path, locatedIndex)
+			if !found || node.Location != test.want {
+				t.Fatalf("location at %s = %#v, want %#v", test.path, node, test.want)
+			}
+		}
+	}
+	walkDocument(located, Path{}, func(_ Path, node *document.Node) {
+		for _, entry := range node.Mapping {
+			if entry.KeyLocation != entry.Value.Location || entry.ValueLocation != entry.Value.Location {
+				t.Fatal("entry and value locations disagree")
+			}
+		}
+	})
+	before := decoded.final.Mapping[0].Value.Mapping[0].Value.Text
+	located.Mapping[0].Value.Mapping[0].Value.Text = "changed snapshot"
+	if decoded.final.Mapping[0].Value.Mapping[0].Value.Text != before || input.Mapping[0].Value.Mapping[0].Value.Text != "source" {
+		t.Fatal("location projection changed a borrowed input")
+	}
+}
+
+func TestIndexedNearestLocationsPreserveMissingAndSyntheticCoordinates(t *testing.T) {
+	root := parseDocumentForDecode(t, "mapping: {'0': value}\nitems: [{value: source}]\nscalar: stop\n")
+	lookup := buildDocumentLookup(root)
+	for _, path := range []Path{Path{}, Keys("missing"), Keys("mapping", "missing"), Keys("mapping", "0"), Keys("mapping").Index(0), Keys("items").Index(4), Keys("items").Index(0).Key("missing"), Keys("scalar", "child"), Path{}.Index(-1)} {
+		want, wantOK := nearestDocumentLocation(root, path)
+		got, gotOK := nearestDocumentLocationWithLookup(root, path, lookup)
+		if got != want || gotOK != wantOK {
+			t.Fatalf("nearest location changed for %s: %#v/%t, want %#v/%t", path, got, gotOK, want, wantOK)
+		}
+	}
+	final := parseDocumentForDecode(t, "value: cli\n")
+	synthetic := Location{SourceID: "cli-1"}
+	metadata := Metadata{fields: map[string]FieldInfo{"/value": {Origin: Origin{Layer: LayerCLI, Locations: []Location{synthetic}}}}}
+	located := documentWithMetadataLocations(final, metadata, root)
+	if location := located.Mapping[0].Value.Location; location.SourceID != "cli-1" || location.Line != 0 || location.Column != 0 {
+		t.Fatalf("synthetic CLI location was replaced by fallback: %#v", location)
+	}
+}

internal/engine/override_context.go

@@ -171,16 +171,23 @@ func documentWithMetadataLocations(root *document.Node, metadata Metadata, fallb
 	if len(fallback) != 0 {
 		fallbackRoot = fallback[0]
 	}
+	var lookup *documentLookup
+	fallbackLocation := func(path Path) (document.Location, bool) {
+		if lookup == nil {
+			lookup = buildDocumentLookup(fallbackRoot)
+		}
+		return nearestDocumentLocationWithLookup(fallbackRoot, path, lookup)
+	}
 	var visit func(*document.Node, Path)
 	visit = func(node *document.Node, path Path) {
 		pointer := path.String()
 		if info, exists := metadata.fields[pointer]; exists {
 			if location, ok := metadataFieldLocation(metadata, pointer, info.Origin); ok {
 				node.Location = location
-			} else if location, ok := nearestDocumentLocation(fallbackRoot, path); ok {
+			} else if location, ok := fallbackLocation(path); ok {
 				node.Location = location
 			}
-		} else if location, ok := nearestDocumentLocation(fallbackRoot, path); ok {
+		} else if location, ok := fallbackLocation(path); ok {
 			node.Location = location
 		}
 		switch node.Kind {
@@ -192,11 +199,11 @@ func documentWithMetadataLocations(root *document.Node, metadata Metadata, fallb
 					if location, ok := metadataFieldLocation(metadata, childPath.String(), info.Origin); ok {
 						entry.KeyLocation = location
 						entry.ValueLocation = location
-					} else if location, ok := nearestDocumentLocation(fallbackRoot, childPath); ok {
+					} else if location, ok := fallbackLocation(childPath); ok {
 						entry.KeyLocation = location
 						entry.ValueLocation = location
 					}
-				} else if location, ok := nearestDocumentLocation(fallbackRoot, childPath); ok {
+				} else if location, ok := fallbackLocation(childPath); ok {
 					entry.KeyLocation = location
 					entry.ValueLocation = location
 				}

internal/engine/validation.go

@@ -124,6 +124,10 @@ func validationMutationDiagnostic(path Path) Diagnostic {
 }
 
 func nearestDocumentLocation(root *document.Node, path Path) (document.Location, bool) {
+	return nearestDocumentLocationWithLookup(root, path, nil)
+}
+
+func nearestDocumentLocationWithLookup(root *document.Node, path Path, lookup *documentLookup) (document.Location, bool) {
 	if root == nil || !path.valid() {
 		return document.Location{}, false
 	}
@@ -135,18 +139,22 @@ func nearestDocumentLocation(root *document.Node, path Path) (document.Location,
 			if segment.kind == pathSegmentIndex {
 				return nearest, locationKnown(nearest)
 			}
-			found := false
+			position := -1
-			for _, entry := range current.Mapping {
+			if lookup != nil {
-				if entry.Key == segment.key {
+				position = lookup.find(current, segment.key)
-					current = entry.Value
+			} else {
-					nearest = current.Location
+				for index, entry := range current.Mapping {
-					found = true
+					if entry.Key == segment.key {
-					break
+						position = index
+						break
+					}
 				}
 			}
-			if !found {
+			if position < 0 {
 				return nearest, locationKnown(nearest)
 			}
+			current = current.Mapping[position].Value
+			nearest = current.Location
 		case document.Sequence:
 			index, ok := schemaIndex(segment)
 			if !ok || index >= len(current.Sequence) {