Commits on Jan 3, 2016

1. syntax: don't pick up chan chains (channel of channels) …

   This is a very weird error. We want to show an error if the chan
   statement is in form of:
   
   	<- chan
   	chan <-
   
   The correct form should be of course:
   
   	<-chan
   	chan<-
   
   But for example, if we have a channel of channels (like below), the
   selected piece of whitespace is also highlighted as an error
   
   	chan<- chan<-
   	      ^
   
   Because it's the part of `<- chan`, whereas we should not treat as an
   error because we have two `chan<-` and `chan<-` statements.
   
   To fix this, we add a `negative lookbehind` regex statement. It will not
   match a text if it's preceded with other text.
   
   First let assemble the current regex for the case: `<- chan`
   (receive-only annotation), which is:
   
   	\(<-\)\@<=\s\+\(chan\>\)\@=
   
   The first part is:
   
   	\(<-\)\@<=\s\+\
   
   Here the pattern \@<= matches with zero width if the preceding atom
   matches just before what follows. `\s\+` means white space of at least
   one character. So it matches **whitespaces** which precedes the
   statement `<-`
   
   Now the second part is only useful with the first part. I've added the
   placeholder to make it more readable:
   
   	PLACEHOLDER(chan\>\)\@="
   
   First the pattern `\@=` means to match the preceding atom with zero
   width. So it will match the **PLACEHOLDER** till it finds a `chan`
   statement. Once it finds it, it doesn't proceed anymore. So we only
   highlight the whitespaces between `<-` and `chan` only if we have a
   white space of at least one character
   
   Finally we can introduce our fix now. We're going to pick the `<-`
   statemetn if it doesn't follow a `chan`. So `chan<-` should NOT trigger
   an error anymore, because we're not going to pick arrows in that form.
   
   To match an arrow which doesn't follow a chan statement can be done via
   a `negative lookbehind`, which is in the form of:
   
   	\(\<chan\>\)\@<!<-
   
   This literally means: "Match `<-` only if it doesn't follow `chan`.
   We're going to use this pattern for the plain `<-` pattern. We also fix
   the issue of only matching `chan` and not words like `mychan`. Aslo note
   we're just going to replace this into our current regex:
   
   This original regex:
   
   	\(<-\)\@<=\s\+\(\<chan\>\)\@=
   
   will be changed into:
   
   	\(\(\<chan\>\)\@<!<-\)\@<=\s\+\(\<chan\>\)\@=
   
   Fixes #655

   

   fatih committed Jan 3, 2016
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