Propagate DuplicateProtoPathError as typed error from new compiler path

go.mod

@@ -18,7 +18,7 @@ require (
 	connectrpc.com/connect v1.19.2
 	connectrpc.com/grpcreflect v1.3.0
 	connectrpc.com/otelconnect v0.9.0
-	github.com/bufbuild/protocompile v0.14.2-0.20260427235036-6b040a6b602b
+	github.com/bufbuild/protocompile v0.14.2-0.20260428232503-17b06932e73e
 	github.com/bufbuild/protoplugin v0.0.0-20260414125817-25d1d281b46b
 	github.com/cli/browser v1.3.0
 	github.com/gofrs/flock v0.13.0

go.sum

@@ -42,8 +42,8 @@ github.com/bmatcuk/doublestar/v4 v4.10.0 h1:zU9WiOla1YA122oLM6i4EXvGW62DvKZVxIe6
 github.com/bmatcuk/doublestar/v4 v4.10.0/go.mod h1:xBQ8jztBU6kakFMg+8WGxn0c6z1fTSPVIjEY1Wr7jzc=
 github.com/brianvoe/gofakeit/v6 v6.28.0 h1:Xib46XXuQfmlLS2EXRuJpqcw8St6qSZz75OUo0tgAW4=
 github.com/brianvoe/gofakeit/v6 v6.28.0/go.mod h1:Xj58BMSnFqcn/fAQeSK+/PLtC5kSb7FJIq4JyGa8vEs=
-github.com/bufbuild/protocompile v0.14.2-0.20260427235036-6b040a6b602b h1:cPYlWl0BN1bITspyWdVW5B1Z3e7WYWFeJIiIpOi3O6g=
-github.com/bufbuild/protocompile v0.14.2-0.20260427235036-6b040a6b602b/go.mod h1:DhgqsRznX/F0sGkUYtTQJRP+q8xMReQRQ3qr+n1opWU=
+github.com/bufbuild/protocompile v0.14.2-0.20260428232503-17b06932e73e h1:wwAUu3QGBzfHahrk6uEymIqvs1XwG55GtHjc/ooOTYM=
+github.com/bufbuild/protocompile v0.14.2-0.20260428232503-17b06932e73e/go.mod h1:DhgqsRznX/F0sGkUYtTQJRP+q8xMReQRQ3qr+n1opWU=
 github.com/bufbuild/protoplugin v0.0.0-20260414125817-25d1d281b46b h1:b7wvo9ZhjLzCp7tGbOUMvgtYTnd33zGSAmMxcdxMnhQ=
 github.com/bufbuild/protoplugin v0.0.0-20260414125817-25d1d281b46b/go.mod h1:c5D8gWRIZ2HLWO3gXYTtUfw/hbJyD8xikv2ooPxnklQ=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=

private/bufpkg/bufimage/build_image.go

@@ -128,8 +128,19 @@ func compileImage(
 		return nil, err
 	}
 
+	// Validate that there is a single result for all files.
+	if len(results) != 1 {
+		return nil, fmt.Errorf("expected a single result from query, instead got: %d", len(results))
+	}
+
+	// Check for fatal errors before processing diagnostics so that callers can
+	// inspect typed errors (e.g. DuplicateProtoPathError) via errors.As. Spanless
+	// diagnostics that accompany these fatal errors are suppressed in the loop below.
+	if results[0].Fatal != nil {
+		return nil, results[0].Fatal
+	}
+
 	var fileAnnotations []bufanalysis.FileAnnotation
-	var rawErrors []error
 	for _, diagnostic := range diagnostics.Diagnostics {
 		if diagnostic.Level() > report.Error {
 			// We only surface [report.Error] level or more severe diagnostics as build errors.
@@ -138,12 +149,9 @@ func compileImage(
 		}
 		primary := diagnostic.Primary()
 		if primary.IsZero() {
-			// Diagnostics without a source span (e.g. file-open errors such as
-			// DuplicateProtoPathError) cannot be represented as FileAnnotations.
-			// Surface them as raw errors so callers see the full message.
-			if diagnostic.File() != "" {
-				rawErrors = append(rawErrors, errors.New(diagnostic.Message()))
-			}
+			// Spanless diagnostics (e.g. from file-open errors like DuplicateProtoPathError)
+			// are companion messages to fatal errors already handled above. Suppress them here
+			// so their typed errors are preserved for callers rather than being lost as strings.
 			continue
 		}
 		start := primary.Location(primary.Start, length.Bytes)
@@ -174,21 +182,9 @@ func compileImage(
 			),
 		)
 	}
-	if len(rawErrors) > 0 {
-		return nil, errors.Join(rawErrors...)
-	}
 	if len(fileAnnotations) > 0 {
 		return nil, bufanalysis.NewFileAnnotationSet(fileAnnotations...)
 	}
-
-	// Validate that there is a single result for all files
-	if len(results) != 1 {
-		return nil, fmt.Errorf("expected a single result from query, instead got: %d", len(results))
-	}
-
-	if results[0].Fatal != nil {
-		return nil, results[0].Fatal
-	}
 	fds, resolver, err := resolverForFDS(results[0].Value)
 	if err != nil {
 		return nil, err