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cmd/gofmt: breaks channel syntax #10040

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bgeron opened this issue Feb 28, 2015 · 2 comments
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cmd/gofmt: breaks channel syntax #10040

bgeron opened this issue Feb 28, 2015 · 2 comments
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@bgeron
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bgeron commented Feb 28, 2015

In Go 1.4.1, gofmt reformats chan <-chan int to chan<- chan int. The two are different in the AST, and indeed gofmt can break working source; see http://play.golang.org/p/L9xzobGwob for an example.

I'm using Ubuntu amd64. It is reproducible on my machine and in the Playground as follows:

  1. Run. This succeeds.
  2. Format. This succeeds.
  3. Run. This fails.
@minux
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minux commented Feb 28, 2015

This is working as intended.

"chan <-chan int" is parsed as "chan<- (chan int)", so if you want "chan (<-chan int)",
you have to use parenthesis. Thus gofmt is actually correct to reformat that way, and
it shows the actual meaning of that type.

http://golang.org/ref/spec#Channel_types
...
The <- operator associates with the leftmost chan possible
...

And I don't understand how your example http://play.golang.org/p/L9xzobGwob
can be broken by gofmt.

@minux minux closed this as completed Feb 28, 2015
@mikioh mikioh changed the title gofmt breaks channel syntax cmd/gofmt: breaks channel syntax Feb 28, 2015
@bgeron
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bgeron commented Mar 1, 2015

Ah, I think I got confused by my own example. Apologies!

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