issue43671.go

     1  // Copyright 2021 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package p
     6  
     7  type C0 interface{ int }
     8  type C1 interface{ chan int }
     9  type C2 interface{ chan int | <-chan int }
    10  type C3 interface{ chan int | chan float32 }
    11  type C4 interface{ chan int | chan<- int }
    12  type C5[T any] interface{ ~chan T | <-chan T }
    13  
    14  func _[T any](ch T) {
    15  	<-ch // ERRORx `cannot receive from ch .* \(no core type\)`
    16  }
    17  
    18  func _[T C0](ch T) {
    19  	<-ch // ERROR "cannot receive from non-channel ch"
    20  }
    21  
    22  func _[T C1](ch T) {
    23  	<-ch
    24  }
    25  
    26  func _[T C2](ch T) {
    27  	<-ch
    28  }
    29  
    30  func _[T C3](ch T) {
    31  	<-ch // ERRORx `cannot receive from ch .* \(no core type\)`
    32  }
    33  
    34  func _[T C4](ch T) {
    35  	<-ch // ERROR "cannot receive from send-only channel"
    36  }
    37  
    38  func _[T C5[X], X any](ch T, x X) {
    39  	x = <-ch
    40  }
    41  
    42  // test case from issue, slightly modified
    43  type RecvChan[T any] interface {
    44  	~chan T | ~<-chan T
    45  }
    46  
    47  func _[T any, C RecvChan[T]](ch C) T {
    48  	return <-ch
    49  }
    50  
    51  func f[T any, C interface{ chan T }](ch C) T {
    52  	return <-ch
    53  }
    54  
    55  func _(ch chan int) {
    56  	var x int = f(ch) // test constraint type inference for this case
    57  	_ = x
    58  }
    59
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