Leveled fields: Fields present only at certain log levels

[ChannyClaus]

#1078

Added just DebugField for now per the suggestions in the issue. Extending this should be very straight-forward if need be.

[ChannyClaus]

Making this attribute a pointer seemed the cleanest way to implement this - doing so would make all existing fields' Level attribute be nil.

[ChannyClaus]

needed to duplicate this in order to be able to pass the address of the DebugLevel for assignment (https://github.com/uber-go/zap/pull/1251/files#diff-b494c03820a49f9efc491691ed31a2acc16d4cebf39d679ffd74bf97bbee968bR45)

DebugLevel doesn't work because https://github.com/uber-go/zap/blob/master/level.go#L32 already uses that name in the same package.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.09%. Comparing base (845ca51) to head (175582f).
Report is 82 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1251   +/-   ##
=======================================
  Coverage   98.08%   98.09%           
=======================================
  Files          50       50           
  Lines        3240     3252   +12     
=======================================
+ Hits         3178     3190   +12     
  Misses         53       53           
  Partials        9        9           

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[prashantv]

Doing this in the ioCore means that this won't work with other cores. For example, this won't work with zaptest/observer.

Edit: I think the implementation of this could live in CheckedEntry to work with all cores.

[ChannyClaus]

Doing this in the ioCore means that this won't work with other cores. For example, this won't work with zaptest/observer.

ah darn - thanks for taking a look! will look into it when i get a chance :.)

[ChannyClaus]

@prashantv moved the filtering over to where you pointed out in the comment - sorry about the incorrect change earlier.

not super sure if https://github.com/uber-go/zap/pull/1251/files#diff-4a689f7bcb3f92ee8d87b3d9070215a7fcb37680843003657a60357c6a821d90R273 is also necessary since all invocations of OnWrite seem to not use the field argument:

$ git grep 'func.*OnWrite'
logger_test.go:func (h *customWriteHook) OnWrite(_ *zapcore.CheckedEntry, _ []Field) {
zapcore/entry.go:func (a CheckWriteAction) OnWrite(ce *CheckedEntry, _ []Field) {
zapcore/entry_test.go:func (c *customHook) OnWrite(_ *CheckedEntry, _ []Field) {

let me know what you think!