cmd/compile: improve error when setting unexported fields

Improve the error user experience when users try to set/refer
to unexported fields and methods of struct literals, by directly saying

    "cannot refer to unexported field or method"

Fixes #31053

Change-Id: I6fd3caf64b7ca9f9d8ea60b7756875e340792d59
Reviewed-on: https://go-review.googlesource.com/c/go/+/201657
Run-TryBot: Emmanuel Odeke <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

src/cmd/compile/internal/gc/typecheck.go

@@ -2967,6 +2967,8 @@ func typecheckcomplit(n *Node) (res *Node) {
  if ci := lookdot1(nil, l.Sym, t, t.Fields(), 2); ci != nil { // Case-insensitive lookup.
  if visible(ci.Sym) {
  yyerror("unknown field '%v' in struct literal of type %v (but does have %v)", l.Sym, t, ci.Sym)
+ } else if nonexported(l.Sym) && l.Sym.Name == ci.Sym.Name { // Ensure exactness before the suggestion.
+ yyerror("cannot refer to unexported field '%v' in struct literal of type %v", l.Sym, t)
  } else {
  yyerror("unknown field '%v' in struct literal of type %v", l.Sym, t)
  }
@@ -3070,6 +3072,11 @@ func visible(sym *types.Sym) bool {
  return sym != nil && (types.IsExported(sym.Name) || sym.Pkg == localpkg)
 }
 
+// nonexported reports whether sym is an unexported field.
+func nonexported(sym *types.Sym) bool {
+ return sym != nil && !types.IsExported(sym.Name)
+}
+
 // lvalue etc
 func islvalue(n *Node) bool {
  switch n.Op {

test/fixedbugs/issue25727.go

@@ -9,13 +9,13 @@ package main
 import "net/http"
 
 var s = http.Server{}
-var _ = s.doneChan // ERROR "s.doneChan undefined .cannot refer to unexported field or method doneChan.$"
-var _ = s.DoneChan // ERROR "s.DoneChan undefined .type http.Server has no field or method DoneChan.$"
+var _ = s.doneChan  // ERROR "s.doneChan undefined .cannot refer to unexported field or method doneChan.$"
+var _ = s.DoneChan  // ERROR "s.DoneChan undefined .type http.Server has no field or method DoneChan.$"
 var _ = http.Server{tlsConfig: nil} // ERROR "unknown field 'tlsConfig' in struct literal.+ .but does have TLSConfig.$"
-var _ = http.Server{DoneChan: nil} // ERROR "unknown field 'DoneChan' in struct literal of type http.Server$"
+var _ = http.Server{DoneChan: nil}  // ERROR "unknown field 'DoneChan' in struct literal of type http.Server$"
 
 type foo struct {
- bar int
+ bar int
 }
 
 var _ = &foo{bAr: 10} // ERROR "unknown field 'bAr' in struct literal.+ .but does have bar.$"

test/fixedbugs/issue31053.dir/f1.go

@@ -0,0 +1,18 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package f1
+
+type Foo struct {
+ doneChan chan bool
+ Name string
+ fOO int
+ hook func()
+}
+
+func (f *Foo) Exported() {
+}
+
+func (f *Foo) unexported() {
+}

test/fixedbugs/issue31053.dir/main.go

@@ -0,0 +1,42 @@
+// errorcheck
+
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+import "./f1"
+
+func main() {
+ f := f1.Foo{
+ doneChan: nil, // ERROR "cannot refer to unexported field 'doneChan' in struct literal of type f1.Foo"
+ DoneChan: nil, // ERROR "unknown field 'DoneChan' in struct literal of type f1.Foo"
+ Name: "hey",
+ name: "there", // ERROR "unknown field 'name' in struct literal of type f1.Foo .but does have Name."
+ noSuchPrivate: true, // ERROR "unknown field 'noSuchPrivate' in struct literal of type f1.Foo"
+ NoSuchPublic: true, // ERROR "unknown field 'NoSuchPublic' in struct literal of type f1.Foo"
+ foo: true, // ERROR "unknown field 'foo' in struct literal of type f1.Foo"
+ hook: func() {}, // ERROR "cannot refer to unexported field 'hook' in struct literal of type f1.Foo"
+ unexported: func() {}, // ERROR "unknown field 'unexported' in struct literal of type f1.Foo"
+ Exported: func() {}, // ERROR "unknown field 'Exported' in struct literal of type f1.Foo"
+ }
+ f.doneChan = nil // ERROR "f.doneChan undefined .cannot refer to unexported field or method doneChan."
+ f.DoneChan = nil // ERROR "f.DoneChan undefined .type f1.Foo has no field or method DoneChan."
+ f.name = nil // ERROR "f.name undefined .type f1.Foo has no field or method name, but does have Name."
+
+ _ = f.doneChan // ERROR "f.doneChan undefined .cannot refer to unexported field or method doneChan."
+ _ = f.DoneChan // ERROR "f.DoneChan undefined .type f1.Foo has no field or method DoneChan."
+ _ = f.Name
+ _ = f.name // ERROR "f.name undefined .type f1.Foo has no field or method name, but does have Name."
+ _ = f.noSuchPrivate // ERROR "f.noSuchPrivate undefined .type f1.Foo has no field or method noSuchPrivate."
+ _ = f.NoSuchPublic // ERROR "f.NoSuchPublic undefined .type f1.Foo has no field or method NoSuchPublic."
+ _ = f.foo // ERROR "f.foo undefined .type f1.Foo has no field or method foo."
+ _ = f.Exported
+ _ = f.exported // ERROR "f.exported undefined .type f1.Foo has no field or method exported, but does have Exported."
+ _ = f.Unexported // ERROR "f.Unexported undefined .type f1.Foo has no field or method Unexported."
+ _ = f.unexported // ERROR "f.unexported undefined .cannot refer to unexported field or method f1..\*Foo..unexported."
+ f.unexported = 10 // ERROR "f.unexported undefined .cannot refer to unexported field or method f1..\*Foo..unexported."
+ f.unexported() // ERROR "f.unexported undefined .cannot refer to unexported field or method f1..\*Foo..unexported."
+ _ = f.hook // ERROR "f.hook undefined .cannot refer to unexported field or method hook."
+}

test/fixedbugs/issue31053.go

@@ -0,0 +1,7 @@
+// errorcheckdir
+
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ignored