fix: escape proto comments correctly in generated descriptions and schemas (#100)

cmd/protoc-gen-go-mcp/mcp.go

@@ -129,7 +129,7 @@ func generateMCPTool(g *protogen.GeneratedFile, method *protogen.Method, mcpServ
 	g.P("func (s *", unexport(mcpServerName), ") ", method.GoName, "Tool() *", mcpPackage.Ident("Tool"), " {")
 	g.P("return &", mcpPackage.Ident("Tool"), "{")
 	g.P("Name: \"", method.GoName, "\",")
-	g.P("Description: \"", methodDescription, "\",")
+	g.P("Description: ", strconv.Quote(methodDescription), ",")
 	g.P("InputSchema: ", jsonPackage.Ident("RawMessage"), "(", quoteBacktickString(string(schemaJSON)), "),")
 	g.P("}")
 	g.P("}")
@@ -172,36 +172,50 @@ func generateHandler(g *protogen.GeneratedFile, method *protogen.Method, mcpServ
 }
 
 // processCommentToString turns a (possibly multi-line, possibly
-// block-style) leading proto comment into a single-line, double-quote-safe
-// string suitable for embedding in a Go string literal.
+// block-style) leading proto comment into a single-line string with its
+// raw text otherwise untouched: callers are responsible for escaping it
+// for whatever they embed it in (a Go string literal via strconv.Quote, a
+// JSON Schema "description" via encoding/json), so this never escapes
+// quotes or backslashes itself - doing so here would corrupt the text when
+// a caller's own encoding escapes it a second time.
 func processCommentToString(comments protogen.Comments) string {
-	// Remove comment markers and clean up the text
+	// protogen.Comments strings for a line comment ("// foo") already
+	// have the "// " prefix stripped from the first line and a trailing
+	// newline, but each continuation line still has its own "// " (the
+	// source text between consecutive "//" markers, including that
+	// prefix, becomes part of the comment string); a block comment
+	// ("/* foo */") instead keeps its "/* " prefix and " */" suffix on
+	// the string as a whole, with no per-line marker to strip. Strip the
+	// block markers first, then strip any remaining per-line "// " below
+	// (a no-op for an already-prefix-stripped block comment).
 	commentText := string(comments)
 
-	// Remove leading comment markers and spaces
 	commentText = strings.TrimPrefix(commentText, "// ")
 	commentText = strings.TrimPrefix(commentText, "/* ")
-
-	// Replace newlines with spaces
-	commentText = strings.ReplaceAll(commentText, "\n// ", " ")
-	commentText = strings.ReplaceAll(commentText, "\n", " ")
-
-	// Remove trailing comment markers
 	commentText = strings.TrimSuffix(commentText, " */")
 
-	// Clean up extra whitespace
-	commentText = strings.TrimSpace(commentText)
+	// Join every line (dropping any remaining "// " line-comment prefix)
+	// into a single space-separated line.
+	lines := strings.Split(commentText, "\n")
+	for i, line := range lines {
+		lines[i] = strings.TrimPrefix(line, "// ")
+	}
+	commentText = strings.Join(lines, " ")
 
-	// Replace multiple spaces with a single space
-	spaceRegex := regexp.MustCompile(`\s+`)
-	commentText = spaceRegex.ReplaceAllString(commentText, " ")
+	commentText = strings.TrimSpace(commentText)
 
-	// Escape quotes to prevent JSON issues
-	commentText = strings.ReplaceAll(commentText, "\"", "\\\"")
+	// Collapse runs of whitespace (including the spaces just introduced
+	// for blank comment lines) into a single space.
+	commentText = whitespaceRunRegexp.ReplaceAllString(commentText, " ")
 
 	return commentText
 }
 
+// whitespaceRunRegexp matches one or more consecutive whitespace
+// characters, used by processCommentToString to collapse them to a single
+// space.
+var whitespaceRunRegexp = regexp.MustCompile(`\s+`)
+
 func generateMcpServerStruct(g *protogen.GeneratedFile, mcpServerName string, clientName string) {
 	g.P("type ", unexport(mcpServerName), " struct {")
 	g.P(clientName)

cmd/protoc-gen-go-mcp/mcp_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/compiler/protogen"
 )
 
 func TestUnexport(t *testing.T) {
@@ -15,3 +16,49 @@ func TestQuoteBacktickString(t *testing.T) {
 	assert.Equal(t, "`abc`", quoteBacktickString("abc"))
 	assert.Equal(t, `"a`+"`"+`b"`, quoteBacktickString("a`b"))
 }
+
+// TestProcessCommentToString covers the two bugs in issue #100: a
+// backslash or backtick in a proto comment must come through completely
+// untouched (callers, not this function, are responsible for escaping the
+// text for whatever they embed it in), and a double quote must likewise
+// come through unescaped rather than backslash-escaped here (which used to
+// make json.Marshal double-escape it when schema.go embedded the result in
+// a JSON Schema "description").
+func TestProcessCommentToString(t *testing.T) {
+	tests := []struct {
+		name string
+		in   protogen.Comments
+		want string
+	}{
+		{
+			name: "quote",
+			in:   protogen.Comments(` Must match "chill" exactly.` + "\n"),
+			want: `Must match "chill" exactly.`,
+		},
+		{
+			name: "backslash",
+			in:   protogen.Comments(` Must match \d+.` + "\n"),
+			want: `Must match \d+.`,
+		},
+		{
+			name: "backtick",
+			in:   protogen.Comments(" Use the `vibe` field.\n"),
+			want: "Use the `vibe` field.",
+		},
+		{
+			name: "multiline joins with a single space",
+			in:   protogen.Comments(" First line.\n Second line.\n"),
+			want: "First line. Second line.",
+		},
+		{
+			name: "block comment",
+			in:   protogen.Comments("/* Block \"comment\" with \\backslash\\. */"),
+			want: `Block "comment" with \backslash\.`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, processCommentToString(tt.in))
+		})
+	}
+}

examples/gen/example/v1/e2e_test.go

@@ -250,12 +250,12 @@ func TestToolsList(t *testing.T) {
 	// fields, named with their protojson (lowerCamel) JSON name, not
 	// nested under a property named after the request message.
 	setVibe := byName["SetVibe"]
-	require.Equal(t, `This is a block comment with multiple lines to test block handling "Hello World"`, setVibe.Description)
+	require.Equal(t, "This is a block comment with multiple lines to test block handling \"Hello World\", a `backtick`, and a path like C:\\vibes\\new", setVibe.Description)
 	require.Equal(t, "object", setVibe.InputSchema["type"])
 	require.Equal(t, false, setVibe.InputSchema["additionalProperties"])
 	require.Equal(t, map[string]any{
 		"vibe": map[string]any{
-			"description": "The vibe of the server to be set",
+			"description": "The vibe of the server to be set. Must match \\d+ or a `code` like \"chill\", and must not contain a literal newline.",
 			"type":        "string",
 		},
 	}, setVibe.InputSchema["properties"])

examples/protos/example.proto

@@ -6,7 +6,8 @@ option go_package = "examples/gen/example/v1;examplev1";
 
 // The request to set the vibe of the server
 message SetVibeRequest {
-  //The vibe of the server to be set
+  // The vibe of the server to be set. Must match \d+ or a `code` like
+  // "chill", and must not contain a literal newline.
   string vibe = 1;
 }
 
@@ -150,7 +151,7 @@ service VibeService {
  * This is a block comment
  * with multiple lines
  * to test block handling
- * "Hello World"
+ * "Hello World", a `backtick`, and a path like C:\vibes\new
  */
   rpc SetVibe(SetVibeRequest) returns (SetVibeResponse) {}
   // Get Vibe