feat: errors/errorsutil: add ErrorWithLocation{}, `NewErrorWithLo…

…cation()`

errors/errorsutil/error_with_location.go

@@ -0,0 +1,32 @@
+package errorsutil
+
+import (
+	"fmt"
+	"runtime"
+)
+
+// ErrorWithLocation represents an error message with code file and line locaiton.
+// It is automatically populated when instantiated with `NewErrorWithLocation()`,
+// and follows the `errors.Error` interface.
+type ErrorWithLocation struct {
+	Msg  string
+	File string
+	Line int
+}
+
+func (e *ErrorWithLocation) Error() string {
+	return fmt.Sprintf("%s (at %s:%d)", e.Msg, e.File, e.Line)
+}
+
+func NewErrorWithLocation(msg string) error {
+	_, file, line, ok := runtime.Caller(1)
+	if !ok {
+		file = "unknown"
+		line = -1
+	}
+	return &ErrorWithLocation{
+		Msg:  msg,
+		File: file,
+		Line: line,
+	}
+}

errors/errorsutil/error_with_location_test.go

@@ -0,0 +1,34 @@
+package errorsutil
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+var errorWithLocationTests = []struct {
+	fn           func() error
+	errMsgSuffix string
+}{
+	{func() error { _, err := time.Parse(time.RFC3339, "Mon, 2024-12-31"); return err }, "github.com/grokify/mogo/errors/errorsutil/error_with_location_test.go:22"},
+}
+
+func TestErrorWithLocation(t *testing.T) {
+	for _, tt := range errorWithLocationTests {
+		try := tt.fn()
+		if try == nil {
+			panic("no error")
+		}
+		tryWithLocation := NewErrorWithLocation(try.Error())
+		idx, idxCalc, ok := isSuffixOnly(tryWithLocation.Error(), tt.errMsgSuffix)
+		if !ok {
+			t.Errorf("errorsutil.NewErrorWithLocation(\"%s\"): mismatch want suffix (%s) got (%s), idx (%d) idxCalc (%d)", tryWithLocation.Error(), tt.errMsgSuffix, tryWithLocation.Error(), idx, idxCalc)
+		}
+	}
+}
+
+func isSuffixOnly(s, substr string) (int, int, bool) {
+	idx := strings.Index(s, substr)
+	idxCalc := len(s) - len(substr) - 1
+	return idx, idxCalc, idx == idxCalc
+}