attributes: format non-Stringer, non-string types as %T=%v

Avoid formatting errors (%!p(...)) on value types and pointers when
formatting attributes, while preserving full type and value information.

Author: pefoley2

attributes/attributes.go

@@ -137,12 +137,16 @@ func (a *Attributes) String() string {
 }
 
 func str(x any) (s string) {
+	if x == nil {
+		return "<nil>"
+	}
 	if v, ok := x.(fmt.Stringer); ok {
 		return fmt.Sprint(v)
-	} else if v, ok := x.(string); ok {
+	}
+	if v, ok := x.(string); ok {
 		return v
 	}
-	return fmt.Sprintf("<%p>", x)
+	return fmt.Sprintf("%T=%v", x, x)
 }
 
 // MarshalJSON helps implement the json.Marshaler interface, thereby rendering

attributes/attributes_test.go

@@ -67,6 +67,7 @@ func ExampleAttributes_WithValue() {
 
 func ExampleAttributes_String() {
 	type key struct{}
+	type namedKey string
 	var typedNil *stringerVal
 	a1 := attributes.New(key{}, typedNil)            // typed nil implements [fmt.Stringer]
 	a2 := attributes.New(key{}, (*stringerVal)(nil)) // typed nil implements [fmt.Stringer]
@@ -76,6 +77,7 @@ func ExampleAttributes_String() {
 	a6 := attributes.New(key{}, stringerVal{s: "two"})
 	a7 := attributes.New(key{}, stringVal{s: "two"})
 	a8 := attributes.New(1, true)
+	a9 := attributes.New(namedKey("my.custom.key"), "val")
 	fmt.Println("a1:", a1.String())
 	fmt.Println("a2:", a2.String())
 	fmt.Println("a3:", a3.String())
@@ -84,15 +86,17 @@ func ExampleAttributes_String() {
 	fmt.Println("a6:", a6.String())
 	fmt.Println("a7:", a7.String())
 	fmt.Println("a8:", a8.String())
+	fmt.Println("a9:", a9.String())
 	// Output:
-	// a1: {"<%!p(attributes_test.key={})>": "<nil>" }
-	// a2: {"<%!p(attributes_test.key={})>": "<nil>" }
-	// a3: {"<%!p(attributes_test.key={})>": "<0x0>" }
-	// a4: {"<%!p(attributes_test.key={})>": "<%!p(<nil>)>" }
-	// a5: {"<%!p(attributes_test.key={})>": "<%!p(int=1)>" }
-	// a6: {"<%!p(attributes_test.key={})>": "two" }
-	// a7: {"<%!p(attributes_test.key={})>": "<%!p(attributes_test.stringVal={two})>" }
-	// a8: {"<%!p(int=1)>": "<%!p(bool=true)>" }
+	// a1: {"attributes_test.key={}": "<nil>" }
+	// a2: {"attributes_test.key={}": "<nil>" }
+	// a3: {"attributes_test.key={}": "*attributes_test.stringVal=<nil>" }
+	// a4: {"attributes_test.key={}": "<nil>" }
+	// a5: {"attributes_test.key={}": "int=1" }
+	// a6: {"attributes_test.key={}": "two" }
+	// a7: {"attributes_test.key={}": "attributes_test.stringVal={two}" }
+	// a8: {"int=1": "bool=true" }
+	// a9: {"attributes_test.namedKey=my.custom.key": "val" }
 }
 
 // Test that two attributes with different content are not Equal.