source mode: support specifying interfaces

CHANGELOG.md

@@ -4,7 +4,9 @@ All notable changes to this project will be documented in this file.
 This project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
-- No changes yet.
+### Added
+- Source mode: support for specifying a subset of interfaces to mock
+  via a comma-separated list argument.
 
 ## 0.6.0 (18 Aug 2025)
 ### Added

README.md

@@ -61,13 +61,18 @@ mockgen -archive=pkg.a database/sql/driver Conn,Driver
 ### Source mode
 
 Source mode generates mock interfaces from a source file.
-It is enabled by using the -source flag. Other flags that
-may be useful in this mode are -imports and -aux_files.
+It is enabled by using the -source flag.
+By default, it generates mocks for all interfaces in the file.
+You can specify a comma-separated list of interfaces to generate
+using a single non-flag argument.
+Other flags that may be useful in this mode are -imports,
+-aux_files and -exclude_interfaces.
 
 Example:
 
 ```bash
 mockgen -source=foo.go [other options]
+mockgen -source=foo.go [other options] SomeInterface,OtherInterface
 ```
 
 ### Package mode

mockgen/internal/tests/exclude/interfaces.go

@@ -1,6 +1,7 @@
 package exclude
 
 //go:generate mockgen -source=interfaces.go -destination=mock.go -package=exclude -exclude_interfaces=IgnoreMe,IgnoreMe2
+//go:generate mockgen -source=interfaces.go -destination=ignore/mock.go IgnoreMe
 
 type IgnoreMe interface {
 	A() bool

mockgen/mockgen.go

@@ -95,7 +95,16 @@ func main() {
 	case *modelGob != "": // gob mode
 		pkg, err = gobMode(*modelGob)
 	case *source != "": // source mode
-		pkg, err = sourceMode(*source)
+		if flag.NArg() > 1 {
+			usage()
+			log.Fatal("Expected at most one argument with -source")
+		}
+		var ifaces []string
+		if flag.NArg() == 1 {
+			ifaces = strings.Split(flag.Arg(0), ",")
+		}
+
+		pkg, err = sourceMode(*source, ifaces)
 	case *archive != "": // archive mode
 		checkArgs()
 		packageName = flag.Arg(0)
@@ -256,10 +265,15 @@ func usage() {
 const usageText = `mockgen has three modes of operation: archive, source and package.
 
 Source mode generates mock interfaces from a source file.
-It is enabled by using the -source flag. Other flags that
-may be useful in this mode are -imports, -aux_files and -exclude_interfaces.
+It is enabled by using the -source flag.
+By default, it generates mocks for all interfaces in the file.
+You can specify a comma-separated list of interfaces to generate
+using a single non-flag argument.
+Other flags that may be useful in this mode are -imports, -aux_files and
+-exclude_interfaces.
 Example:
 	mockgen -source=foo.go [other options]
+	mockgen -source=foo.go [other options] SomeInterface,OtherInterface
 
 Package mode works by specifying the package and interface names.
 It is enabled by passing two non-flag arguments: an import path, and a

mockgen/parse.go

@@ -36,7 +36,35 @@ import (
 )
 
 // sourceMode generates mocks via source file.
-func sourceMode(source string) (*model.Package, error) {
+//
+// ifaces is a list of interface names to generate mocks for.
+// If nil or empty, all interfaces in the source file are used.
+func sourceMode(source string, ifaces []string) (*model.Package, error) {
+	var wantIface func(name string) bool
+	if len(ifaces) == 0 {
+		wantIface = func(name string) bool { return true }
+	} else {
+		wantIfaces := make(map[string]struct{})
+		for _, n := range ifaces {
+			wantIfaces[n] = struct{}{}
+		}
+		wantIface = func(name string) bool {
+			_, ok := wantIfaces[name]
+			return ok
+		}
+	}
+
+	if *excludeInterfaces != "" {
+		oldWantIface := wantIface
+		excludeNamesSet := parseExcludeInterfaces(*excludeInterfaces)
+		wantIface = func(name string) bool {
+			if _, ok := excludeNamesSet[name]; ok {
+				return false
+			}
+			return oldWantIface(name)
+		}
+	}
+
 	srcDir, err := filepath.Abs(filepath.Dir(source))
 	if err != nil {
 		return nil, fmt.Errorf("failed getting source directory: %v", err)
@@ -59,6 +87,7 @@ func sourceMode(source string) (*model.Package, error) {
 		importedInterfaces: newInterfaceCache(),
 		auxInterfaces:      newInterfaceCache(),
 		srcDir:             srcDir,
+		wantIface:          wantIface,
 	}
 
 	// Handle -imports.
@@ -75,10 +104,6 @@ func sourceMode(source string) (*model.Package, error) {
 		}
 	}
 
-	if *excludeInterfaces != "" {
-		p.excludeNamesSet = parseExcludeInterfaces(*excludeInterfaces)
-	}
-
 	// Handle -aux_files.
 	if err := p.parseAuxFiles(*auxFiles); err != nil {
 		return nil, err
@@ -167,7 +192,7 @@ type fileParser struct {
 	auxFiles           []*ast.File
 	auxInterfaces      *interfaceCache
 	srcDir             string
-	excludeNamesSet    map[string]struct{}
+	wantIface          func(name string) bool
 }
 
 func (p *fileParser) errorf(pos token.Pos, format string, args ...any) error {
@@ -228,7 +253,7 @@ func (p *fileParser) parseFile(importPath string, file *ast.File) (*model.Packag
 
 	var is []*model.Interface
 	for ni := range iterInterfaces(file) {
-		if _, ok := p.excludeNamesSet[ni.name.String()]; ok {
+		if p.wantIface != nil && !p.wantIface(ni.name.String()) {
 			continue
 		}
 		i, err := p.parseInterface(ni.name.String(), importPath, ni)

mockgen/parse_test.go

@@ -109,7 +109,7 @@ func checkGreeterImports(t *testing.T, imports map[string]importedPackage) {
 func Benchmark_parseFile(b *testing.B) {
 	source := "internal/tests/performance/big_interface/big_interface.go"
 	for n := 0; n < b.N; n++ {
-		sourceMode(source)
+		sourceMode(source, nil)
 	}
 }
 
@@ -143,3 +143,19 @@ func TestParseArrayWithConstLength(t *testing.T) {
 		}
 	}
 }
+
+func TestSourceMode_interfaceSubset(t *testing.T) {
+	pkg, err := sourceMode("internal/tests/exclude/interfaces.go", []string{"IgnoreMe"})
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	if want, got := 1, len(pkg.Interfaces); want != got {
+		t.Fatalf("Expected %d interfaces but got %d", want, got)
+	}
+
+	iface := pkg.Interfaces[0]
+	if want, got := "IgnoreMe", iface.Name; want != got {
+		t.Fatalf("Expected interface name to be %s but got %s", want, got)
+	}
+}