feat(context): adding lazy evaluated value

README.md

@@ -222,7 +222,7 @@ The `oops.OopsError` builder must finish with either `.Errorf(...)`, `.Wrap(...)
 
 | Builder method                    | Getter                                  | Description                                                                                                                                                                                |
 | --------------------------------- | --------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
-| `.With(string, any)`              | `err.Context() map[string]any`          | Supply a list of attributes key+value                                                                                                                                                      |
+| `.With(string, any)`              | `err.Context() map[string]any`          | Supply a list of attributes key+value. Values of type `func() any {}` are accepted and evaluated lazily.                                                                                   |
 | `.Code(string)`                   | `err.Code() string`                     | Set a code or slug that describes the error. Error messages are intented to be read by humans, but such code is expected to be read by machines and be transported over different services |
 | `.Time(time.Time)`                | `err.Time() time.Time`                  | Set the error time (default: `time.Now()`)                                                                                                                                                 |
 | `.Since(time.Time)`               | `err.Duration() time.Duration`          | Set the error duration                                                                                                                                                                     |
@@ -255,6 +255,7 @@ err3 := oops.
     With("driver", "postgresql").
     With("query", query).
     With("query.duration", queryDuration).
+    With("lorem", func() string { return "ipsum" }).	// lazy evaluation
     Errorf("could not fetch user")
 
 // with trace+span

error.go

@@ -123,11 +123,13 @@ func (o OopsError) Tags() []string {
 
 // Context returns a k/v context of the error.
 func (o OopsError) Context() map[string]any {
-	return mergeNestedErrorMap(
-		o,
-		func(e OopsError) map[string]any {
-			return e.context
-		},
+	return lazyMapEvaluation(
+		mergeNestedErrorMap(
+			o,
+			func(e OopsError) map[string]any {
+				return e.context
+			},
+		),
 	)
 }
 
@@ -180,11 +182,13 @@ func (o OopsError) User() (string, map[string]any) {
 			return e.userID
 		},
 	)
-	userData := mergeNestedErrorMap(
-		o,
-		func(e OopsError) map[string]any {
-			return e.userData
-		},
+	userData := lazyMapEvaluation(
+		mergeNestedErrorMap(
+			o,
+			func(e OopsError) map[string]any {
+				return e.userData
+			},
+		),
 	)
 
 	return userID, userData
@@ -198,11 +202,13 @@ func (o OopsError) Tenant() (string, map[string]any) {
 			return e.tenantID
 		},
 	)
-	tenantData := mergeNestedErrorMap(
-		o,
-		func(e OopsError) map[string]any {
-			return e.tenantData
-		},
+	tenantData := lazyMapEvaluation(
+		mergeNestedErrorMap(
+			o,
+			func(e OopsError) map[string]any {
+				return e.tenantData
+			},
+		),
 	)
 
 	return tenantID, tenantData

examples/log/example.go

@@ -15,7 +15,7 @@ func d() error {
 		In("authz").
 		Time(time.Now()).
 		With("user_id", 1234).
-		With("permission", "post.create").
+		With("permission", func() any { return "post.create" }). // lazy evaluation
 		Hint("Runbook: https://doc.acme.org/doc/abcd.md").
 		User("user-123", "firstname", "john", "lastname", "doe").
 		Errorf("permission denied")

go.work.sum

@@ -1,5 +1,6 @@
 github.com/google/go-cmp v0.5.8/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/mod v0.6.0/go.mod h1:4mET923SAdbXp2ki8ey+zGs1SLqsuM2Y0uvdZR/fUNI=
+golang.org/x/net v0.1.0/go.mod h1:Cx3nUiGt4eDBEyega/BKRp+/AlGL8hYe7U9odMt2Cco=
 golang.org/x/tools v0.2.0/go.mod h1:y4OqIKeOV/fWJetJ8bXPU1sEVniLMIyDAZWeHdV+NTA=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

kv.go

@@ -0,0 +1,30 @@
+package oops
+
+import (
+	"reflect"
+)
+
+func lazyMapEvaluation(data map[string]any) map[string]any {
+	for key, value := range data {
+		switch v := value.(type) {
+		case map[string]any:
+			data[key] = lazyMapEvaluation(v)
+		default:
+			data[key] = lazyValueEvaluation(value)
+		}
+	}
+
+	return data
+}
+func lazyValueEvaluation(value any) any {
+	v := reflect.ValueOf(value)
+	if !v.IsValid() || v.Kind() != reflect.Func {
+		return value
+	}
+
+	if v.Type().NumIn() != 0 || v.Type().NumOut() != 1 {
+		return value
+	}
+
+	return v.Call([]reflect.Value{})[0].Interface()
+}

oops_test.go

@@ -138,6 +138,15 @@ func TestOopsWith(t *testing.T) {
 	is.Equal(err.(OopsError).context, map[string]any{"user_id": 1234, "foo": "bar"})
 }
 
+func TestOopsWithLazyEvaluation(t *testing.T) {
+	is := assert.New(t)
+
+	// lazy evaluation
+	err := new().With("user_id", func() int { return 1234 }, "foo", map[string]any{"bar": func() string { return "baz" }}).Wrap(assert.AnError)
+	is.Error(err)
+	is.Equal(err.(OopsError).Context(), map[string]any{"user_id": 1234, "foo": map[string]any{"bar": "baz"}})
+}
+
 func TestOopsHint(t *testing.T) {
 	is := assert.New(t)