feat: remove examples/foo.go and add fixer.go for enhanced functionality

- **Why remove examples/foo.go?** The functions within were likely deemed unnecessary or have been refactored into a more comprehensive solution.

- **Why add fixer.go?** Introduces a utility for modifying Go source files, possibly to automate code refactoring or corrections, enhancing the development workflow.

refactor(main.go): streamline flag parsing and function removal logic
feat(main.go): add JSON schema support for dead code analysis
feat(schema.go): introduce JSON schema for deadcode output analysis
feat(testdata): add test files and examples for dead code analysis

feat(testdata/stringer.go): add new myString struct implementing fmt.Stringer

This commit introduces a new file `stringer.go` within the `testdata` directory, which defines a `myString` struct. This struct implements the `fmt.Stringer` interface, ensuring that instances of `myString` can be easily converted to a string using the `String()` method. This addition aims to enhance the codebase by providing a clear and idiomatic way to convert `myString` instances to strings, following Go's convention of using the `Stringer` interface for string representations of types.

fixer.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"os"
+)
+
+func fix(filename, functionName string) error {
+	start, end, err := lookup(filename, functionName)
+	if err != nil {
+		return err
+	}
+
+	if err := rewrite(filename, start, end); err != nil {
+		return err
+	}
+	return nil
+}
+
+func lookup(filename, functionName string) (int, int, error) {
+	fset := token.NewFileSet()
+	node, err := parser.ParseFile(fset, filename, nil, parser.ParseComments)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	var start, end int
+	ast.Inspect(node, func(n ast.Node) bool {
+		funcDecl, ok := n.(*ast.FuncDecl)
+		if ok && funcDecl.Name.Name == functionName {
+			start = fset.Position(funcDecl.Pos()).Line
+			end = fset.Position(funcDecl.End()).Line
+			return false
+		}
+		return true
+	})
+	if start == 0 || end == 0 {
+		return 0, 0, fmt.Errorf("func %s not found in %s", functionName, filename)
+	}
+	return start, end, nil
+}
+
+func rewrite(filename string, start, end int) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	buf := new(bytes.Buffer)
+	scanner := bufio.NewScanner(file)
+	for l := 1; scanner.Scan(); {
+		if l < start || l > end {
+			if _, err := buf.Write(append(scanner.Bytes(), '\n')); err != nil {
+				return err
+			}
+		}
+		l++
+	}
+	if err := scanner.Err(); err != nil {
+		return err
+	}
+
+	// run gofmt
+	b, err := format.Source(buf.Bytes())
+	if err != nil {
+		return err
+	}
+	// write to file
+	info, err := file.Stat()
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(filename, b, info.Mode()); err != nil {
+		return err
+	}
+	return nil
+}

main.go

@@ -1,81 +1,59 @@
 package main
 
 import (
-	"bufio"
-	"bytes"
+	"encoding/json"
 	"flag"
-	"go/ast"
-	"go/format"
-	"go/parser"
-	"go/token"
+	"io"
 	"log"
 	"os"
 )
 
+// flags
 var (
-	fileName, functionName string
+	jsonFlag     = flag.String("json", "", "JSON file generated by deadcode")
+	fileFlag     = flag.String("file", "", "File to remove function from")
+	functionFlag = flag.String("function", "", "Function to remove")
 )
 
 func main() {
-	flag.StringVar(&fileName, "f", "", "File to remove function from (shorthand)")
-	flag.StringVar(&fileName, "file", "", "File to remove function from")
-	flag.StringVar(&functionName, "fn", "", "File to remove function from (shorthand)")
-	flag.StringVar(&functionName, "function", "", "Function to remove")
 	flag.Parse()
 
-	if fileName == "" || functionName == "" {
-		flag.Usage()
-		os.Exit(1)
-	}
-
-	fset := token.NewFileSet()
-	node, err := parser.ParseFile(fset, fileName, nil, parser.ParseComments)
-	if err != nil {
-		log.Fatalf("Failed to parse file: %v", err)
-	}
-
-	var start, end int
-	ast.Inspect(node, func(n ast.Node) bool {
-		fn, ok := n.(*ast.FuncDecl)
-		if ok && fn.Name.Name == functionName {
-			start = fset.Position(fn.Pos()).Line
-			end = fset.Position(fn.End()).Line
-			return false
+	// run specific fixer
+	if f, fn := *fileFlag, *functionFlag; f != "" && fn != "" {
+		if err := fix(f, fn); err != nil {
+			log.Fatal(err)
 		}
-		return true
-	})
-
-	file, err := os.Open(fileName)
-	if err != nil {
-		log.Fatalf("Failed to open file: %v", err)
-	}
-	defer file.Close()
-
-	buf := new(bytes.Buffer)
-	scanner := bufio.NewScanner(file)
-	for l := 1; scanner.Scan(); {
-		if l < start || l > end {
-			if _, err := buf.Write(append(scanner.Bytes(), '\n')); err != nil {
-				log.Fatalf("Failed to write to buffer: %v", err)
-			}
+		return
+	}
+	// run fixer by reading JSON
+	var r io.Reader
+	switch v := *jsonFlag; v {
+	case "", "-":
+		r = os.Stdin
+	default:
+		f, err := os.Open(v)
+		if err != nil {
+			log.Fatalf("failed to open file %s: %v", v, err)
 		}
-		l++
+		defer f.Close()
+		r = f
 	}
-	if err := scanner.Err(); err != nil {
-		log.Fatalf("Failed to read file: %v", err)
+	if err := run(r); err != nil {
+		log.Fatal(err)
 	}
+}
 
-	// run gofmt
-	b, err := format.Source(buf.Bytes())
-	if err != nil {
-		log.Fatalf("Failed to format source: %v", err)
+func run(r io.Reader) error {
+	packages := []Package{}
+	if err := json.NewDecoder(r).Decode(&packages); err != nil {
+		return err
 	}
-	// write to file
-	info, err := file.Stat()
-	if err != nil {
-		log.Fatalf("Failed to get file info: %v", err)
-	}
-	if err := os.WriteFile(fileName, b, info.Mode()); err != nil {
-		log.Fatalf("Failed to write to file: %v", err)
+	for _, p := range packages {
+		for _, f := range p.Funcs {
+			if err := fix(f.Position.File, f.Name); err != nil {
+				return err
+			}
+		}
 	}
+	return nil
 }

schema.go

@@ -0,0 +1,28 @@
+package main
+
+// This file contains the JSON schema for the deadcode output.
+// https://pkg.go.dev/golang.org/x/tools@v0.20.0/cmd/deadcode#hdr-JSON_schema
+
+type Package struct {
+	Name  string     // declared name
+	Path  string     // full import path
+	Funcs []Function // list of dead functions within it
+}
+
+type Function struct {
+	Name      string   // name (sans package qualifier)
+	Position  Position // file/line/column of function declaration
+	Generated bool     // function is declared in a generated .go file
+}
+
+type Edge struct {
+	Initial  string   // initial entrypoint (main or init); first edge only
+	Kind     string   // = static | dynamic
+	Position Position // file/line/column of call site
+	Callee   string   // target of the call
+}
+
+type Position struct {
+	File      string // name of file
+	Line, Col int    // line and byte index, both 1-based
+}

testdata/main.go

@@ -0,0 +1,10 @@
+package main
+
+func main() {
+	Reachable()
+}
+
+func init() {
+	s := myString{Value: "hello"}
+	s.Reachable()
+}

testdata/main_test.go

@@ -0,0 +1,7 @@
+package main
+
+import "testing"
+
+func TestReachableByTest(t *testing.T) {
+	ReachableByTest()
+}

testdata/reachable.go

@@ -0,0 +1,15 @@
+package main
+
+import "fmt"
+
+func Reachable() {
+	fmt.Println("reachable")
+}
+
+func Unreachable() {
+	fmt.Println("unreachable")
+}
+
+func ReachableByTest() {
+	fmt.Println("reachableByTest")
+}

testdata/stringer.go

@@ -0,0 +1,17 @@
+package main
+
+import "fmt"
+
+var _ fmt.Stringer = myString{}
+
+type myString struct {
+	Value string
+}
+
+func (s myString) String() string {
+	return s.Value
+}
+
+func (s myString) Reachable() {
+	return
+}