fix: handle return values in generate-nodebug

This basically matched the existing nodebug version of
gserver/component, modulo generated comments.

Author: mark-rushakoff

gassert/cmd/generate-nodebug/main.go

@@ -159,9 +159,19 @@ package %s`, srcName, f.Name.Name)
 		if err := printer.Fprint(w, fset, fd); err != nil {
 			return err
 		}
-		// We fully removed the function body, so now put empty braces in place.
-		if _, err := io.WriteString(w, " {}"); err != nil {
-			return err
+		// We fully removed the function body.
+		// Whether we leave the body empty or put a naked return,
+		// depends on whether the function has any return values.
+		if fd.Type.Results == nil {
+			if _, err := io.WriteString(w, " {}"); err != nil {
+				return err
+			}
+		} else {
+			// There are results, but we can already be sure they are named,
+			// so a naked return suffices here.
+			if _, err := io.WriteString(w, " {\n\treturn\n}"); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -188,6 +198,25 @@ func stripFunction(fd *ast.FuncDecl) {
 		}
 	}
 
+	// We don't modify the params at all.
+	// If they are named, we keep the names for readability,
+	// and if not, we don't care.
+
+	if fd.Type.Results != nil {
+		for _, field := range fd.Type.Results.List {
+			// Zero-length names means the return value is unnamed.
+			// That is the only time we want to replace the name with an underscore,
+			// in order to use a naked return.
+			// Otherwise we keep the existing names.
+			if len(field.Names) == 0 {
+				field.Names = []*ast.Ident{
+					// We aren't marking the position, but it seems to work fine.
+					&ast.Ident{Name: "_"},
+				}
+			}
+		}
+	}
+
 	// TODO: there are probably comments that would currently leak through,
 	// if they are next to fd.Type.TypeParams or fd.Type.Results.
 }

gassert/cmd/generate-nodebug/main_test.go

@@ -296,3 +296,78 @@ func invariantThirdParty(a pkg1.A) {}
 
 	require.Equal(t, exp, out.String())
 }
+
+func TestRewriteSource_functionsWithReturnValues(t *testing.T) {
+	t.Parallel()
+
+	src := []byte(`//go:build debug
+
+package pathological
+
+import (
+	"io"
+	"errors"
+
+	"example.com/pkg1"
+	"example.com/pkg2"
+)
+
+func invariantReaderNamedReturns(r io.Reader) (n int, err error) {
+	return 1, errors.New("uh oh")
+}
+
+func invariantReaderUnnamedReturns(r io.Reader) (int, error) {
+	return 2, nil
+}
+
+func invariantMultipleUnnamedReturnsSameType() (string, string, string) {
+	return "", "", ""
+}
+
+func invariantMultipleNamedReturnsSameType() (a, b uint) {
+	return 10, 20
+}
+
+func invariantWriterBareSingleReturn(w io.Writer) pkg1.A {
+	return pkg2.DoSomething(w)
+}
+`)
+
+	var out bytes.Buffer
+	require.NoError(t, RewriteSource("r_debug.go", src, &out))
+
+	exp := `//go:build !debug
+
+// Code generated by github.com/rollchains/gordian/gassert/cmd/generate-nodebug r_debug.go; DO NOT EDIT.
+
+package pathological
+
+import (
+	"io"
+
+	"example.com/pkg1"
+)
+
+func invariantReaderNamedReturns(r io.Reader) (n int, err error) {
+	return
+}
+
+func invariantReaderUnnamedReturns(r io.Reader) (_ int, _ error) {
+	return
+}
+
+func invariantMultipleUnnamedReturnsSameType() (_ string, _ string, _ string) {
+	return
+}
+
+func invariantMultipleNamedReturnsSameType() (a, b uint) {
+	return
+}
+
+func invariantWriterBareSingleReturn(w io.Writer) (_ pkg1.A) {
+	return
+}
+`
+
+	require.Equal(t, exp, out.String())
+}

gcosmos/gserver/component.go

@@ -40,6 +40,8 @@ import (
 	"github.com/spf13/viper"
 )
 
+//go:generate go run github.com/rollchains/gordian/gassert/cmd/generate-nodebug component_debug.go
+
 // The various interfaces we expect a Component to satisfy.
 var (
 	_ serverv2.ServerComponent[transaction.Tx] = (*Component)(nil)