Split up into separate pakages (#50)

This is a re-structuring. The functionality remains the same.

a base stackfmt package. This package is just for stack traces and does not do anything with errors.
A separate slogerr package for those looking to add structured errors.
An errwrap package for wrapping and unwrapping errors
Maintain the existing errors package. This is designed as a replacement for the existing errors package that introduces wrapping with stack traces
The errors package will re-export some items from other packages.
However, it is exporting much less overall.

.github/workflows/build.yaml

@@ -15,7 +15,7 @@ jobs:
       - id: govulncheck
         uses: golang/govulncheck-action@v1
         with:
-           go-version-input: 1.21.1
+           go-version-input: 1.23.4
            go-package: ./...
            cache: true
 
@@ -24,19 +24,19 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Golang
-        uses: actions/setup-go@v4
+        uses: actions/setup-go@v5
         with:
-          go-version: '1.21.1'
+          go-version: '1.23.4'
           cache: false
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v3
+        uses: golangci/golangci-lint-action@v6
         with:
           # Require: The version of golangci-lint to use.
           # When `install-mode` is `binary` (default) the value can be v1.2 or v1.2.3 or `latest` to use the latest version.
           # When `install-mode` is `goinstall` the value can be v1.2.3, `latest`, or the hash of a commit.
-          version: v1.54
+          version: v1.60
           args: --timeout=5m --allow-parallel-runners
 
   build:
@@ -51,7 +51,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v4
         with:
-          go-version: '1.21'
+          go-version: '1.23.4'
 
       - name: build and test
         shell: bash

base.go

@@ -0,0 +1,47 @@
+package errors
+
+import (
+	"fmt"
+	"reflect"
+)
+
+func formatterPlusV(s fmt.State, verb rune, err error) {
+	if f, ok := err.(fmt.Formatter); ok {
+		f.Format(s, verb)
+	} else {
+		fmt.Fprintf(s, "%+v", err)
+	}
+}
+
+type unwrapper interface {
+	Unwrap() error
+}
+
+type unwraps interface {
+	Unwrap() []error
+}
+
+type errorUnwrap interface {
+	Unwrap() error
+	// ErrorNoUnwrap is the error message component of the wrapping
+	// It will be a prefix of Error()
+	// If there is no message in the wrapping then this can return an empty string
+	ErrorNoUnwrap() string
+}
+
+func isNil(err error) bool {
+	if err == nil {
+		return true
+	}
+
+	v := reflect.ValueOf(err)
+	k := v.Kind()
+	switch k {
+	case reflect.Pointer, reflect.UnsafePointer, reflect.Interface:
+		return v.IsNil()
+	case reflect.Slice, reflect.Array, reflect.Map:
+		return v.IsNil() || v.Len() == 0
+	}
+
+	return false
+}