Uber Zap logger function name in logs - go

Question

How to get function name printed in logs from Uber Zap logging ?
This is the PR request with which they seemed to have added the functionality to output function names in log.
I am using golang version 1.15 and go.uber.org/zap v1.16.0
This is my code:
package main
import (
"go.uber.org/zap"
)
var logger *zap.Logger
func main() {
logger := NewLogger()
logger.Info("Test msg Main")
TestFunc(logger)
}
func TestFunc(logger *zap.Logger) {
logger.Info("Test msg TestFunc")
}
func NewLogger() *zap.Logger {
config := zap.NewDevelopmentConfig()
opts := []zap.Option{
zap.AddCallerSkip(1), // traverse call depth for more useful log lines
zap.AddCaller(),
}
logger, _ = config.Build(opts...)
return logger
}
This is the output I get with/without the addition of AddCaller() option
2021-03-01T15:00:02.927-0800 INFO runtime/proc.go:204 Test msg Main
2021-03-01T15:00:02.927-0800 INFO cmd/main.go:12 Test msg TestFunc
I am expecting something like
2021-03-01T15:00:02.927-0800 INFO runtime/proc.go:204 main Test msg Main
2021-03-01T15:00:02.927-0800 INFO cmd/main.go:12 TestFunc Test msg TestFunc

Answer 1

By default, the provided encoder presets (NewDevelopmentEncoderConfig used by NewDevelopmentConfig and NewProductionEncoderConfig used by NewProductionConfig) do not enable function name logging.
To enable function name, you need to enable caller (true by default) and set a non-empty value for config.EncoderConfig.FunctionKey.
Source: EncoderConfig
type EncoderConfig struct {
// Set the keys used for each log entry. If any key is empty, that portion
// of the entry is omitted.
...
CallerKey string `json:"callerKey" yaml:"callerKey"`
FunctionKey string `json:"functionKey" yaml:"functionKey"` // this needs to be set
StacktraceKey string `json:"stacktraceKey" yaml:"stacktraceKey"`
...
}
Example Console Logger:
func main() {
config := zap.NewDevelopmentConfig()
// if you're using console encoding, the FunctionKey value can be any
// non-empty string because console encoding does not print the key.
config.EncoderConfig.FunctionKey = "F"
logger, _ := config.Build()
logger.Info("Test Logging")
// Output: 2021-03-03T11:41:47.728+0800 INFO example/main.go:11 main.main Test Logging
}
Example JSON Logger:
func main() {
config := zap.NewProductionConfig()
// the FunctionKey value matters because it will become the JSON field
config.EncoderConfig.FunctionKey = "func"
logger, _ := config.Build()
log(logger)
// Output: {"level":"info","ts":1614743088.538128,"caller":"example/main.go:15","func":"main.log","msg":"Test Logging"}
}
func log(logger *zap.Logger) {
logger.Info("Test Logging")
}