Ensure fields are created for de-aliased struct types

This means that there is a target for defs and refs to refer to after the original fields go away because their corresponding structs have also gone away on a database downgrade.

Author: smowton

go/extractor/extractor.go

@@ -1702,21 +1702,29 @@ func extractTypeWithFlags(tw *trap.Writer, tp types.Type, transparentAliases boo
 			for i := 0; i < tp.NumFields(); i++ {
 				field := tp.Field(i).Origin()
 
-				if !transparentAliases {
-					// ensure the field is associated with a label - note that
-					// struct fields do not have a parent scope, so they are not
-					// dealt with by `extractScopes`.
-
-					// Skip this when extracting a type with transparent aliases;
-					// this is not the definitive version of the type.
-					fieldlbl, exists := tw.Labeler.FieldID(field, i, lbl)
-					if !exists {
-						extractObject(tw, field, fieldlbl)
-					}
+				// ensure the field is associated with a label - note that
+				// struct fields do not have a parent scope, so they are not
+				// dealt with by `extractScopes`.
+
+				// For the transparentAliases case we bypass the object-label cache
+				// because we're extracting a field relative to a synthetic field
+				// that has a different type and therefore label, whereas the label
+				// cache is indexed by object, not type-label.
+				var fieldlbl trap.Label
+				var exists bool
+				if transparentAliases {
+					fieldlbl = tw.Labeler.FieldIDNoCache(field, i, lbl)
+					exists = false
+				} else {
+					fieldlbl, exists = tw.Labeler.FieldID(field, i, lbl)
+				}
 
-					dbscheme.FieldStructsTable.Emit(tw, fieldlbl, lbl)
+				if !exists {
+					extractObject(tw, field, fieldlbl)
 				}
 
+				dbscheme.FieldStructsTable.Emit(tw, fieldlbl, lbl)
+
 				name := field.Name()
 				if field.Embedded() {
 					name = ""

go/extractor/trap/labels.go

@@ -210,6 +210,16 @@ func (l *Labeler) ReceiverObjectID(object types.Object, methlbl Label) (Label, b
 	return label, exists
 }
 
+func (l *Labeler) FieldIDNoCache(field *types.Var, idx int, structlbl Label) Label {
+	name := field.Name()
+	// there can be multiple fields with the blank identifier, so use index to
+	// distinguish them
+	if field.Name() == "_" {
+		name = fmt.Sprintf("_%d", idx)
+	}
+	return l.GlobalID(fmt.Sprintf("{%v},%s;field", structlbl, name))
+}
+
 // FieldID associates a label with the given field and returns it, together with
 // a flag indicating whether the field already had a label associated with it;
 // the field must belong to `structlbl`, since that label is used to construct
@@ -218,13 +228,7 @@ func (l *Labeler) ReceiverObjectID(object types.Object, methlbl Label) (Label, b
 func (l *Labeler) FieldID(field *types.Var, idx int, structlbl Label) (Label, bool) {
 	label, exists := l.objectLabels[field]
 	if !exists {
-		name := field.Name()
-		// there can be multiple fields with the blank identifier, so use index to
-		// distinguish them
-		if field.Name() == "_" {
-			name = fmt.Sprintf("_%d", idx)
-		}
-		label = l.GlobalID(fmt.Sprintf("{%v},%s;field", structlbl, name))
+		label = l.FieldIDNoCache(field, idx, structlbl)
 		l.objectLabels[field] = label
 	}
 	return label, exists