errorgroup: producing a better failure message for a programmer error

[shifengbin]

SetLimit(10)
Go(xx) //start a groutine ,g.done be called if task done
SetLimit(-1) //<-- g.sem=nil

but g.done is not atomic, if g.sem=nil maybe block the goroutine

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Message from Ian Lance Taylor:

Patch Set 1:

(2 comments)

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Message from fengbin shi:

Patch Set 1:

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Message from Bryan Mills:

Patch Set 1:

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Message from fengbin shi:

Patch Set 2:

(2 comments)

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