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Show "<nil>" for nil Stringer. #854

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merged 1 commit into from Aug 28, 2020

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andy-retailnext
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In encodeStringer, instead of returning an error when a panic
occurs when calling String() on a nil pointer, use the string value
"" like the fmt package does.

It is not always possible to handle this case by fixing the
implementation of String to not panic. This requires implementing
String with a pointer receiver, which doesn't work if you need to
be able to call String on non-addressable values.

In encodeStringer, instead of returning an error when a panic
occurs when calling String() on a nil pointer, use the string value
"<nil>" like the fmt package does.

It is not always possible to handle this case by fixing the
implementation of String to not panic. This requires implementing
String with a pointer receiver, which doesn't work if you need to
be able to call String on non-addressable values.
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CLAassistant commented Aug 4, 2020

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codecov bot commented Aug 4, 2020

Codecov Report

Merging #854 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

Impacted file tree graph

@@           Coverage Diff           @@
##           master     #854   +/-   ##
=======================================
  Coverage   98.35%   98.35%           
=======================================
  Files          43       43           
  Lines        2368     2372    +4     
=======================================
+ Hits         2329     2333    +4     
  Misses         32       32           
  Partials        7        7           
Impacted Files Coverage Δ
zapcore/field.go 100.00% <100.00%> (ø)

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@prashantv prashantv left a comment

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I think this is reasonable, it matches the behaviour of the standard library.

@@ -208,7 +208,12 @@ func addFields(enc ObjectEncoder, fields []Field) {
func encodeStringer(key string, stringer interface{}, enc ObjectEncoder) (err error) {
defer func() {
if v := recover(); v != nil {
err = fmt.Errorf("PANIC=%v", v)
val := reflect.ValueOf(stringer)
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This block looks very similar to the logic in the fmt package uses to determine if nil should be used,
https://golang.org/src/fmt/print.go#L540

Should we reference this?

@@ -208,7 +208,12 @@ func addFields(enc ObjectEncoder, fields []Field) {
func encodeStringer(key string, stringer interface{}, enc ObjectEncoder) (err error) {
defer func() {
if v := recover(); v != nil {
err = fmt.Errorf("PANIC=%v", v)
val := reflect.ValueOf(stringer)
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@abhinav abhinav Aug 28, 2020

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Suggested change
val := reflect.ValueOf(stringer)
// See also https://golang.org/src/fmt/print.go#L540.
val := reflect.ValueOf(stringer)

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I'll add the reference to the stdlib as a follow up.

@abhinav abhinav merged commit 663c590 into uber-go:master Aug 28, 2020
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cgxxv pushed a commit to cgxxv/zap that referenced this pull request Mar 25, 2022
In encodeStringer, instead of returning an error when a panic
occurs when calling String() on a nil pointer, use the string value
"<nil>" like the fmt package does.

It is not always possible to handle this case by fixing the
implementation of String to not panic. This requires implementing
String with a pointer receiver, which doesn't work if you need to
be able to call String on non-addressable values.
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4 participants