feat: extract set_fields rule forces Int fields on gff_json merge targets

Glob targets now match via matchPathPattern, so one rule can cover
areas/*.are.json. set_fields runs after preserve/merge so the forced
value always wins.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/pipeline/extract.go

@@ -350,26 +350,48 @@ func mergeExtractedGFFJSON(p *project.Project, target string, extracted *gff.Doc
 	}
 
 	raw, err := os.ReadFile(target)
-	if err != nil {
-		if errors.Is(err, os.ErrNotExist) {
-			return nil
-		}
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
 		return fmt.Errorf("read existing source %s: %w", target, err)
 	}
-	var existing gff.Document
-	if err := json.Unmarshal(raw, &existing); err != nil {
-		return fmt.Errorf("parse existing source %s: %w", target, err)
+	if err == nil {
+		var existing gff.Document
+		if err := json.Unmarshal(raw, &existing); err != nil {
+			return fmt.Errorf("parse existing source %s: %w", target, err)
+		}
+
+		for _, label := range rule.PreserveFields {
+			if field, ok := gffField(existing.Root, label); ok {
+				setGFFField(&extracted.Root, field)
+			}
+		}
+		for _, listRule := range rule.MergeLists {
+			if err := mergeGFFListByKey(&extracted.Root, existing.Root, listRule); err != nil {
+				return err
+			}
+		}
 	}
 
-	for _, label := range rule.PreserveFields {
-		if field, ok := gffField(existing.Root, label); ok {
-			setGFFField(&extracted.Root, field)
+	// set_fields runs last so a forced value also wins over preserve_fields.
+	for _, setRule := range rule.SetFields {
+		if err := setGFFIntField(&extracted.Root, setRule); err != nil {
+			return fmt.Errorf("set_fields on %s: %w", target, err)
 		}
 	}
-	for _, listRule := range rule.MergeLists {
-		if err := mergeGFFListByKey(&extracted.Root, existing.Root, listRule); err != nil {
-			return err
+	return nil
+}
+
+// setGFFIntField forces an existing Int field to a fixed value; a field the
+// document does not have is left absent rather than invented.
+func setGFFIntField(s *gff.Struct, rule project.ExtractSetFieldRule) error {
+	for index, field := range s.Fields {
+		if field.Label != rule.Field {
+			continue
 		}
+		if _, ok := field.Value.(gff.IntValue); !ok {
+			return fmt.Errorf("field %q is %s, not Int", rule.Field, field.Type)
+		}
+		s.Fields[index].Value = gff.IntValue(rule.Value)
+		return nil
 	}
 	return nil
 }
@@ -384,7 +406,7 @@ func extractGFFJSONMergeRule(p *project.Project, target string) (project.Extract
 		return project.ExtractGFFJSONMergeRule{}, false, nil
 	}
 	for _, rule := range p.EffectiveConfig().Extract.Merge.GFFJSON {
-		if rule.Target == rel {
+		if rule.Target == rel || matchPathPattern(rel, rule.Target) {
 			return rule, true, nil
 		}
 	}

internal/pipeline/pipeline_test.go

@@ -3503,6 +3503,100 @@ extract:
 	}
 }
 
+func TestExtractSetsConfiguredGFFJSONFields(t *testing.T) {
+	root := t.TempDir()
+	mustMkdir(t, filepath.Join(root, "src", "module"))
+	mustMkdir(t, filepath.Join(root, "src", "areas"))
+	mustMkdir(t, filepath.Join(root, "assets"))
+	mustMkdir(t, filepath.Join(root, "build"))
+
+	mustWriteFile(t, filepath.Join(root, "nwn-tool.yaml"), `
+module:
+  name: Test Module
+  resref: testmod
+paths:
+  source: src
+  assets: assets
+  build: build
+extract:
+  merge:
+    gff_json:
+      - target: areas/*.are.json
+        set_fields:
+          - field: ChanceRain
+            value: 0
+          - field: ChanceSnow
+            value: 0
+`)
+
+	mustWriteFile(t, filepath.Join(root, "src", "module", "module.ifo.json"), `{
+  "file_type": "IFO ",
+  "file_version": "V3.2",
+  "root": {
+    "struct_type": 0,
+    "fields": [
+      {
+        "label": "Mod_Name",
+        "type": "CExoString",
+        "value": "Test Module"
+      }
+    ]
+  }
+}
+`)
+	mustWriteFile(t, filepath.Join(root, "src", "areas", "area_a.are.json"), `{
+  "file_type": "ARE ",
+  "file_version": "V3.2",
+  "root": {
+    "struct_type": 0,
+    "fields": [
+      {
+        "label": "ChanceRain",
+        "type": "Int",
+        "value": 40
+      },
+      {
+        "label": "WindPower",
+        "type": "Int",
+        "value": 2
+      }
+    ]
+  }
+}
+`)
+
+	p, err := project.Load(root)
+	if err != nil {
+		t.Fatalf("load project: %v", err)
+	}
+	if err := p.ValidateLayout(); err != nil {
+		t.Fatalf("validate layout: %v", err)
+	}
+	if err := p.Scan(); err != nil {
+		t.Fatalf("scan: %v", err)
+	}
+	if _, err := BuildModule(p); err != nil {
+		t.Fatalf("build module: %v", err)
+	}
+	if err := p.Scan(); err != nil {
+		t.Fatalf("rescan before extract: %v", err)
+	}
+	if _, err := Extract(p); err != nil {
+		t.Fatalf("extract: %v", err)
+	}
+
+	document := readGFFJSON(t, filepath.Join(root, "src", "areas", "area_a.are.json"))
+	if got, want := fieldValue(t, document.Root, "ChanceRain"), gff.IntValue(0); got != want {
+		t.Fatalf("expected forced ChanceRain %#v, got %#v", want, got)
+	}
+	if got, want := fieldValue(t, document.Root, "WindPower"), gff.IntValue(2); got != want {
+		t.Fatalf("expected untouched WindPower %#v, got %#v", want, got)
+	}
+	if _, ok := gffField(document.Root, "ChanceSnow"); ok {
+		t.Fatalf("expected absent ChanceSnow to stay absent")
+	}
+}
+
 func TestExtractNormalizesResourceNamesToLowercase(t *testing.T) {
 	root := t.TempDir()
 	mustMkdir(t, filepath.Join(root, "src", "blueprints", "items"))