Merge pull request #10 from m-mizutani/feature/unstack

Add Unstack method

README.md

@@ -73,7 +73,16 @@ if err := someAction("no_such_file.txt"); err != nil {
 exit status 1
 ```
 
-NOTE: If the error is wrapped by `goerr` multiply, `%+v` will print the stack trace of the deepest error.
+**NOTE**: If the error is wrapped by `goerr` multiply, `%+v` will print the stack trace of the deepest error.
+
+**Tips**: If you want not to print the stack trace for current stack frame, you can use `Unstack` method. Also, `UnstackN` method removes the top multiple stack frames.
+
+```go
+if err := someAction("no_such_file.txt"); err != nil {
+	// Unstack() removes the current stack frame from the error message.
+	return goerr.Wrap(err, "failed to someAction").Unstack()
+}
+```
 
 ### Add/Extract contextual variables
 

errors.go

@@ -158,6 +158,18 @@ func (x *Error) With(key string, value any) *Error {
 	return x
 }
 
+// Unstack trims stack trace by 1. It can be used for internal helper or utility functions.
+func (x *Error) Unstack() *Error {
+	x.st = unstack(x.st, 1)
+	return x
+}
+
+// UnstackN trims stack trace by n. It can be used for internal helper or utility functions.
+func (x *Error) UnstackN(n int) *Error {
+	x.st = unstack(x.st, n)
+	return x
+}
+
 // Is returns true if target is goerr.Error and Error.id of two errors are matched. It's for errors.Is. If Error.id is empty, it always returns false.
 func (x *Error) Is(target error) bool {
 	var err *Error

errors_test.go

@@ -177,3 +177,47 @@ func TestLoggerWithNil(t *testing.T) {
 		t.Errorf("Expected log output to contain '\"error\":null', got '%s'", out.String())
 	}
 }
+
+func TestUnstack(t *testing.T) {
+	t.Run("original stack", func(t *testing.T) {
+		err := oops()
+		st := err.Stacks()
+		if st == nil {
+			t.Error("Expected stack trace to be nil")
+		}
+		if len(st) == 0 {
+			t.Error("Expected stack trace length to be 0")
+		}
+		if st[0].Func != "github.com/m-mizutani/goerr_test.oops" {
+			t.Errorf("Not expected stack trace func name (github.com/m-mizutani/goerr_test.oops): %s", st[0].Func)
+		}
+	})
+
+	t.Run("unstacked", func(t *testing.T) {
+		err := oops().Unstack()
+		st1 := err.Stacks()
+		if st1 == nil {
+			t.Error("Expected stack trace to be non-nil")
+		}
+		if len(st1) == 0 {
+			t.Error("Expected stack trace length to be non-zero")
+		}
+		if st1[0].Func != "github.com/m-mizutani/goerr_test.TestUnstack.func2" {
+			t.Errorf("Not expected stack trace func name (github.com/m-mizutani/goerr_test.TestUnstack.func2): %s", st1[0].Func)
+		}
+	})
+
+	t.Run("unstackN with 2", func(t *testing.T) {
+		err := oops().UnstackN(2)
+		st2 := err.Stacks()
+		if st2 == nil {
+			t.Error("Expected stack trace to be non-nil")
+		}
+		if len(st2) == 0 {
+			t.Error("Expected stack trace length to be non-zero")
+		}
+		if st2[0].Func != "testing.tRunner" {
+			t.Errorf("Not expected stack trace func name (testing.tRunner): %s", st2[0].Func)
+		}
+	})
+}

stack.go

@@ -105,16 +105,16 @@ func (f frame) name() string {
 
 // Format of frame formats the frame according to the fmt.Formatter interface.
 //
-//    %s    source file
-//    %d    source line
-//    %n    function name
-//    %v    equivalent to %s:%d
+//	%s    source file
+//	%d    source line
+//	%n    function name
+//	%v    equivalent to %s:%d
 //
 // Format accepts flags that alter the printing of some verbs, as follows:
 //
-//    %+s   function name and path of source file relative to the compile time
-//          GOPATH separated by \n\t (<funcname>\n\t<path>)
-//    %+v   equivalent to %+s:%d
+//	%+s   function name and path of source file relative to the compile time
+//	      GOPATH separated by \n\t (<funcname>\n\t<path>)
+//	%+v   equivalent to %+s:%d
 func (f frame) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 's':
@@ -149,12 +149,12 @@ func (f frame) MarshalText() ([]byte, error) {
 
 // Format formats the stack of Frames according to the fmt.Formatter interface.
 //
-//    %s	lists source files for each Frame in the stack
-//    %v	lists the source file and line number for each Frame in the stack
+//	%s	lists source files for each Frame in the stack
+//	%v	lists the source file and line number for each Frame in the stack
 //
 // Format accepts flags that alter the printing of some verbs, as follows:
 //
-//    %+v   Prints filename, function, and line number for each Frame in the stack.
+//	%+v   Prints filename, function, and line number for each Frame in the stack.
 func (st StackTrace) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 'v':
@@ -208,6 +208,20 @@ func (s *stack) StackTrace() StackTrace {
 	return frames
 }
 
+func unstack(st *stack, n int) *stack {
+	switch {
+	case n <= 0:
+		var ret stack
+		return &ret
+	case n >= len(*st):
+		return st
+
+	default:
+		ret := (*st)[n:]
+		return &ret
+	}
+}
+
 func callers() *stack {
 	const depth = 32
 	var pcs [depth]uintptr