issue32187.go

     1  // run
     2  
     3  // Copyright 2019 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  // short-circuiting interface-to-concrete comparisons
     8  // will not miss panics
     9  
    10  package main
    11  
    12  import (
    13  	"log"
    14  	"strings"
    15  )
    16  
    17  func main() {
    18  	var (
    19  		x interface{}
    20  		p *int
    21  		s []int
    22  		l *interface{}
    23  		r []*int
    24  	)
    25  	tests := []struct {
    26  		name   string
    27  		errStr string
    28  		f      func()
    29  	}{
    30  		{"switch case", "", func() {
    31  			switch x {
    32  			case x.(*int):
    33  			}
    34  		}},
    35  		{"interface conversion", "", func() { _ = x == x.(error) }},
    36  		{"type assertion", "", func() { _ = x == x.(*int) }},
    37  		{"out of bounds", "", func() { _ = x == s[1] }},
    38  		{"nil pointer dereference #1", "", func() { _ = x == *p }},
    39  		// TODO(mdempsky): Restore "nil pointer dereference" check. The Go
    40  		// spec doesn't mandate an order for panics (or even panic
    41  		// messages), but left-to-right is less confusing to users.
    42  		{"nil pointer dereference #2", "", func() { _ = *l == r[0] }},
    43  		{"nil pointer dereference #3", "", func() { _ = *l == any(r[0]) }},
    44  	}
    45  
    46  	for _, tc := range tests {
    47  		testFuncShouldPanic(tc.name, tc.errStr, tc.f)
    48  	}
    49  }
    50  
    51  func testFuncShouldPanic(name, want string, f func()) {
    52  	defer func() {
    53  		e := recover()
    54  		if e == nil {
    55  			log.Fatalf("%s: comparison did not panic\n", name)
    56  		}
    57  		if have := e.(error).Error(); !strings.Contains(have, want) {
    58  			log.Fatalf("%s: wrong panic message: have %q, want %q\n", name, have, want)
    59  		}
    60  	}()
    61  	f()
    62  }
    63
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