[Go] support for select blocks and matching cases inside of those

[hex0punk]

Is your feature request related to a problem? Please describe.
Currently, there is no clean way to write a pattern for this:

func request() {
    c := make(chan int)
    for i := 0; i < 5; i++ {
        i := i
        go func() {
            select {
              case c <- i:
              default:
            }
        }()
    }
}

Describe the solution you'd like
I am interested in finding where the channel send occurs, but because it occurs as a case inside of a select block, there is no way to detect that in semgrep without getting a Pattern could not be parsed as a Golang semgrep pattern error

I would like to specify a pattern like this

  pattern: |
    go func(...) {
      ...
      select {
        case $CHANNEL <- $VAR
      }
      ...
    }(...)
    ...

or even this

    go func(...) {
      ...
      case $CHANNEL <- $VAR
      ...
    }(...)
    ...

to detect where data is sent to a go channel as a case inside select blocks

Describe alternatives you've considered
This won't work where channel sends occur as cases

rules:
- id: test
  pattern: |
    go func(...) {
      ...
      $CHANNEL <- $VAR
      ...
    }(...)
    ...
  message: |
    test
  severity: WARNING

Additional context
This is a very common concurrency pattern in go

[aryx]

I think this is better (which you suggested on slack):

rules:
- id: test
  patterns:
  - pattern: |
        go func(...) {
          ...
          select {
             ... 
             case $CHANNEL <- $VAL
             ...
          }
          ...
        }(...)
        ...
  message: test
  languages: [go]
  severity: WARNING

[hex0punk]

I think this is better (which you suggested on slack):

rules:
- id: test
  patterns:
  - pattern: |
        go func(...) {
          ...
          select {
             ... 
             case $CHANNEL <- $VAL
             ...
          }
          ...
        }(...)
        ...
  message: test
  languages: [go]
  severity: WARNING

yep, agreed

[ievans]

hi @hex0punk, thanks so much for creating an issue! can you share the relative priority of this for you -- is it blocking your adoption of semgrep (p0), a significant problem to using semgrep for you (p1), or a minor annoyance (p2)?

playground link: https://semgrep.dev/s/Nr4L

[hex0punk]

hi @hex0punk, thanks so much for creating an issue! can you share the relative priority of this for you -- is it blocking your adoption of semgrep (p0), a significant problem to using semgrep for you (p1), or a minor annoyance (p2)?

playground link: https://semgrep.dev/s/Nr4L

for sure!

Priority: (p2)
Reason: not a significant problem at the moment, just working on new semgrep rules while I have time. It is a common pattern in go though.

[aryx]

link https://semgrep.dev/s/nqqg/

[aryx]

This works now on develop: https://semgrep.dev/s/nqqg/?version=develop
Note that you need to use 'case ...' inside a select/switch, and not just '...' because
of ambiguities otherwise in the grammar.