Not a spacing error: "<-chan <-chan"

[fxkr]

package main

func main() {
    _ = make(<-chan <-chan struct{})
}

https://play.golang.org/p/CKUYB_PX5D

The space between the two "<-chan" is mistakenly shown as a spacing error.

[fatih]

Hi @fxkr, seem it's caused by the rule for showing errors of chan <-, whereas it's expecting chan<-.

[fatih]

Hi @fxkr, can you please pull #678 and let me know if it works for you?

[fxkr]

Thanks!

Unfortunately, it introduces a regression. This correct code is now hilighted:

var mychan <-chan int

Luckily chan (the keyword) is always a word by itself (<- aren't word chars), so you can just always use \<chan\> instead of chan in all of these regexes and that fixes that, so:

" Spacing errors around the 'chan' keyword
if g:go_highlight_chan_whitespace_error != 0
  " receive-only annotation on chan type
  "
  " \(chan\)\@<!<-  (only pick arrow when it doesn't come after a chan)
  " this prevents picking up 'chan<- chan<-' but not '<- chan'
  syn match goSpaceError display "\(\(\<chan\>\)\@<!<-\)\@<=\s\+\(\<chan\>\)\@="

  " send-only annotation on chan type
  "
  " \(<-\)\@<!chan  (only pick chan when it doesn't come after an arrow)
  " this prevents picking up '<-chan <-chan' but not 'chan <-'
  syn match goSpaceError display "\(\(<-\)\@<!\<chan\>\)\@<=\s\+\(<-\)\@="

  " value-ignoring receives in a few contexts
  syn match goSpaceError display "\(\(^\|[={(,;]\)\s*<-\)\@<=\s\+f"
endif

(Interestingly, the second chan in the first regex already had the \>)

...and that fixes the problem and doesn't introduce any others as far as I can see.

Here's the test file I've been using:

package main

// Set  let g:go_fmt_autosave=0  in vimrc  before saving this file!

func main() {

    // ok = bad code highlighted and good code not highlighted
    // broken = bad code not highlighted or good code highlighted


    // Correctly formatted code
    // ------------------------

    _ = make(<-chan <-chan struct{}) // broken before, fixed

    // https://golang.org/ref/spec#Channel_types
    type _ struct {

        // "The <- operator associates with the leftmost chan possible:"
        _ chan<- chan int   // broken -> ok
        _ chan<- <-chan int // ok
        _ <-chan <-chan int // broken -> ok
        _ chan (<-chan int) // ok

        // "same as ..."
        _ chan<- (chan int)   // ok
        _ chan<- (<-chan int) // ok
        _ <-chan (<-chan int) // ok

        my1chan <-chan int // ok -> broken !!! -> ok with my fix
        my2chan chan<- int // ok -> ok (but probably by accident, because "chan chan<-" is ok)
    }


    // Code containing a single formatting error per line
    // --------------------------------------------------

    type _ struct {

        // Single bad space
        _ chan <- (chan int) // ok
        _ chan<- <- chan int // ok
        _ chan ( <-chan int) // broken

        // Multiple spaces within
        _ chan<-  chan int // ok
        _ chan  (<-chan int) // broken
        _ chan (<-chan  int) // broken
        _ chan<-  <-chan int // broken
    }
}

As you can see, there are some cases of incorrectly formatted code not being highlighted, but that was like that before your patch.