feat(mcp): build flagset from mcp input schema to parse args

cmd/src/mcp.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"strings"
 
 	"github.com/sourcegraph/src-cli/internal/mcp"
 )
@@ -16,7 +17,7 @@ func init() {
 }
 func mcpMain(args []string) error {
 	fmt.Println("NOTE: This command is still experimental")
-	tools, err := mcp.LoadToolDefinitions()
+	tools, err := mcp.LoadDefaultToolDefinitions()
 	if err != nil {
 		return err
 	}
@@ -38,6 +39,33 @@ func mcpMain(args []string) error {
 }
 
 func handleMcpTool(tool *mcp.ToolDef, args []string) error {
-	fmt.Printf("handling tool %q args: %+v", tool.Name, args)
+	fs, vars, err := mcp.BuildArgFlagSet(tool)
+	if err != nil {
+		return err
+	}
+
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	inputSchema := tool.InputSchema
+
+	for _, reqName := range inputSchema.Required {
+		if vars[reqName] == nil {
+			return fmt.Errorf("no value provided for required flag --%s", reqName)
+		}
+	}
+
+	if len(args) < len(inputSchema.Required) {
+		return fmt.Errorf("not enough arguments provided - the following flags are required:\n%s", strings.Join(inputSchema.Required, "\n"))
+	}
+
+	mcp.DerefFlagValues(vars)
+
+	fmt.Println("Flags")
+	for name, val := range vars {
+		fmt.Printf("--%s=%v\n", name, val)
+	}
+
 	return nil
 }

internal/mcp/mcp_args.go

@@ -0,0 +1,75 @@
+package mcp
+
+import (
+	"flag"
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/sourcegraph/sourcegraph/lib/errors"
+)
+
+var _ flag.Value = (*strSliceFlag)(nil)
+
+type strSliceFlag struct {
+	vals []string
+}
+
+func (s *strSliceFlag) Set(v string) error {
+	s.vals = append(s.vals, v)
+	return nil
+}
+
+func (s *strSliceFlag) String() string {
+	return strings.Join(s.vals, ",")
+}
+
+func DerefFlagValues(vars map[string]any) {
+	for k, v := range vars {
+		rfl := reflect.ValueOf(v)
+		if rfl.Kind() == reflect.Pointer {
+			vv := rfl.Elem().Interface()
+			if slice, ok := vv.(strSliceFlag); ok {
+				vv = slice.vals
+			}
+			vars[k] = vv
+		}
+	}
+}
+
+func BuildArgFlagSet(tool *ToolDef) (*flag.FlagSet, map[string]any, error) {
+	if tool == nil {
+		return nil, nil, errors.New("cannot build flagset on nil Tool Definition")
+	}
+	fs := flag.NewFlagSet(tool.Name, flag.ContinueOnError)
+	flagVars := map[string]any{}
+
+	for name, pVal := range tool.InputSchema.Properties {
+		switch pv := pVal.(type) {
+		case *SchemaPrimitive:
+			switch pv.Kind {
+			case "integer":
+				dst := fs.Int(name, 0, pv.Description)
+				flagVars[name] = dst
+
+			case "boolean":
+				dst := fs.Bool(name, false, pv.Description)
+				flagVars[name] = dst
+			case "string":
+				dst := fs.String(name, "", pv.Description)
+				flagVars[name] = dst
+			default:
+				return nil, nil, fmt.Errorf("unknown schema primitive kind %q", pv.Kind)
+
+			}
+		case *SchemaArray:
+			strSlice := new(strSliceFlag)
+			fs.Var(strSlice, name, pv.Description)
+			flagVars[name] = strSlice
+		case *SchemaObject:
+			// not supported yet
+		}
+	}
+
+	return fs, flagVars, nil
+}

internal/mcp/mcp_args_test.go

@@ -0,0 +1,97 @@
+package mcp
+
+import (
+	"testing"
+)
+
+func TestFlagSetParse(t *testing.T) {
+	toolJSON := []byte(`{
+	  "tools": [
+		{
+		  "name": "sg_test_tool",
+		  "description": "test description",
+		  "inputSchema": {
+			"type": "object",
+			"$schema": "https://localhost/schema-draft/2025-07",
+			"required": ["values"],
+			"properties": {
+			  "repos": {
+				"type": "array",
+				"items": {
+				  "type": "string"
+				}
+			  },
+			  "tag": {
+				"type": "string",
+				"items": true
+			  },
+			  "count": {
+				"type": "integer"
+	          },
+	          "boolFlag": {
+				"type": "boolean"
+	          }
+			}
+		  },
+		  "outputSchema": {
+			"type": "object",
+			"$schema": "https://localhost/schema-draft/2025-07",
+			"properties": {
+			  "result": { "type": "string" }
+			}
+		  }
+		}
+	  ]
+	}`)
+
+	defs, err := loadToolDefinitions(toolJSON)
+	if err != nil {
+		t.Fatalf("failed to load tool json: %v", err)
+	}
+
+	flagSet, vars, err := BuildArgFlagSet(defs["test-tool"])
+	if err != nil {
+		t.Fatalf("failed to build flagset from mcp tool definition: %v", err)
+	}
+
+	if len(vars) == 0 {
+		t.Fatalf("vars from buildArgFlagSet should not be empty")
+	}
+
+	args := []string{"-repos=A", "-repos=B", "-count=10", "-boolFlag", "-tag=testTag"}
+
+	if err := flagSet.Parse(args); err != nil {
+		t.Fatalf("flagset parsing failed: %v", err)
+	}
+	DerefFlagValues(vars)
+
+	if v, ok := vars["repos"].([]string); ok {
+		if len(v) != 2 {
+			t.Fatalf("expected flag 'repos' values to have length %d but got %d", 2, len(v))
+		}
+	} else {
+		t.Fatalf("expected flag 'repos' to have type of []string but got %T", v)
+	}
+	if v, ok := vars["tag"].(string); ok {
+		if v != "testTag" {
+			t.Fatalf("expected flag 'tag' values to have value %q but got %q", "testTag", v)
+		}
+	} else {
+		t.Fatalf("expected flag 'tag' to have type of string but got %T", v)
+	}
+	if v, ok := vars["count"].(int); ok {
+		if v != 10 {
+			t.Fatalf("expected flag 'count' values to have value %d but got %d", 10, v)
+		}
+	} else {
+		t.Fatalf("expected flag 'count' to have type of int but got %T", v)
+	}
+	if v, ok := vars["boolFlag"].(bool); ok {
+		if v != true {
+			t.Fatalf("expected flag 'boolFlag' values to have value %v but got %v", true, v)
+		}
+	} else {
+		t.Fatalf("expected flag 'boolFlag' to have type of bool but got %T", v)
+	}
+
+}

internal/mcp/mcp_parse.go

@@ -68,7 +68,7 @@ type parser struct {
 	errors []error
 }
 
-func LoadToolDefinitions() (map[string]*ToolDef, error) {
+func LoadDefaultToolDefinitions() (map[string]*ToolDef, error) {
 	return loadToolDefinitions(mcpToolListJSON)
 }