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ebd34e3e45
In this test, traditionally the comparison `*l == r[0]` was left as a
comparison between `*l` (type `any`) and `r[0]` (type `*int`), and the
rest of the compiler needed to handle mixed-typed comparisons.
However, this means more complexity for wiring up explicit rtypes.
To simplify rtype handling, the next CL will change unified IR to
instead handle the expression as `*l == any(r[0])`. However, a
consequence of this currently is that walk will now sequence the
`any(r[0])` expression first, because it involves a
concrete-to-interface conversion. And in turn, this means the `r[0]`
panic ("index out of bounds") will take priority over the `*l`
panic ("nil pointer dereference").
This is a change in user-visible semantics in some cases, but the Go
spec leaves this unspecified, so it shouldn't be an issue. Note also:
gccgo has the same behavior (i.e., panicking on index out of bounds,
not nil pointer dereference), and cmd/compile also already has the
same behavior when the interface conversion is explicit (as in the
added "nil pointer dereference #3" test case).
Updates #23735.
Updates #32187.
Change-Id: I49e5dcca85b4680f9c8780ef0013e64254d38fe5
Reviewed-on: https://go-review.googlesource.com/c/go/+/418097
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
63 lines
1.5 KiB
Go
63 lines
1.5 KiB
Go
// run
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// short-circuiting interface-to-concrete comparisons
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// will not miss panics
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package main
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import (
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"log"
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"strings"
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)
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func main() {
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var (
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x interface{}
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p *int
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s []int
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l *interface{}
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r []*int
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)
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tests := []struct {
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name string
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errStr string
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f func()
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}{
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{"switch case", "", func() {
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switch x {
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case x.(*int):
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}
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}},
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{"interface conversion", "", func() { _ = x == x.(error) }},
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{"type assertion", "", func() { _ = x == x.(*int) }},
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{"out of bounds", "", func() { _ = x == s[1] }},
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{"nil pointer dereference #1", "", func() { _ = x == *p }},
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// TODO(mdempsky): Restore "nil pointer dereference" check. The Go
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// spec doesn't mandate an order for panics (or even panic
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// messages), but left-to-right is less confusing to users.
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{"nil pointer dereference #2", "", func() { _ = *l == r[0] }},
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{"nil pointer dereference #3", "", func() { _ = *l == any(r[0]) }},
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}
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for _, tc := range tests {
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testFuncShouldPanic(tc.name, tc.errStr, tc.f)
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}
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}
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func testFuncShouldPanic(name, want string, f func()) {
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defer func() {
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e := recover()
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if e == nil {
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log.Fatalf("%s: comparison did not panic\n", name)
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}
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if have := e.(error).Error(); !strings.Contains(have, want) {
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log.Fatalf("%s: wrong panic message: have %q, want %q\n", name, have, want)
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}
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}()
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f()
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}
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