cmd/cgo: special case C ptr types to use uintptr

Some C types are declared as pointers, but C code
stores non-pointers in them.  When the Go garbage
collector sees such a pointer, it gets unhappy.

Instead, for these types represent them on the Go
side with uintptr.

We need this change to handle Apple's CoreFoundation
CF*Ref types. Users of these types might need to
update their code like we do in root_cgo_darwin.go.
The only change that is required under normal
circumstances is converting some nils to 0.
A go fix module is provided to help.

Fixes #21897

RELNOTE=yes

Change-Id: I9716cfb255dc918792625f42952aa171cd31ec1b
Reviewed-on: https://go-review.googlesource.com/66332
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

3 files changed, 334 insertions, 0 deletions

diff --git a/src/cmd/fix/cftype.go b/src/cmd/fix/cftype.go
new file mode 100644
index 0000000000..da1627fbfb
--- /dev/null
+++ b/src/cmd/fix/cftype.go
@@ -0,0 +1,93 @@
+// Copyright 2017 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 main
+
+import (
+	"go/ast"
+	"go/token"
+	"reflect"
+	"strings"
+)
+
+func init() {
+	register(cftypeFix)
+}
+
+var cftypeFix = fix{
+	name:     "cftype",
+	date:     "2017-09-27",
+	f:        cftypefix,
+	desc:     `Fixes initializers of C.CF*Ptr types`,
+	disabled: false,
+}
+
+// Old state:
+//   type CFTypeRef unsafe.Pointer
+// New state:
+//   type CFTypeRef uintptr
+// and similar for other CF*Ref types.
+// This fix finds nils initializing these types and replaces the nils with 0s.
+func cftypefix(f *ast.File) bool {
+	if !imports(f, "C") {
+		return false
+	}
+	typeof, _ := typecheck(&TypeConfig{}, f)
+
+	// step 1: Find all the nils with the offending types.
+	// Compute their replacement.
+	badNils := map[interface{}]ast.Expr{}
+	walk(f, func(n interface{}) {
+		if i, ok := n.(*ast.Ident); ok && i.Name == "nil" && badPointerType(typeof[n]) {
+			badNils[n] = &ast.BasicLit{ValuePos: i.NamePos, Kind: token.INT, Value: "0"}
+		}
+	})
+	if len(badNils) == 0 {
+		return false
+	}
+
+	// step 2: find all uses of the bad nils, replace them with 0.
+	// There's no easy way to map from an ast.Expr to all the places that use them, so
+	// we use reflect to find all such references.
+	exprType := reflect.TypeOf((*ast.Expr)(nil)).Elem()
+	exprSliceType := reflect.TypeOf(([]ast.Expr)(nil))
+	walk(f, func(n interface{}) {
+		if n == nil {
+			return
+		}
+		v := reflect.ValueOf(n)
+		if v.Type().Kind() != reflect.Ptr {
+			return
+		}
+		if v.IsNil() {
+			return
+		}
+		v = v.Elem()
+		if v.Type().Kind() != reflect.Struct {
+			return
+		}
+		for i := 0; i < v.NumField(); i++ {
+			f := v.Field(i)
+			if f.Type() == exprType {
+				if r := badNils[f.Interface()]; r != nil {
+					f.Set(reflect.ValueOf(r))
+				}
+			}
+			if f.Type() == exprSliceType {
+				for j := 0; j < f.Len(); j++ {
+					e := f.Index(j)
+					if r := badNils[e.Interface()]; r != nil {
+						e.Set(reflect.ValueOf(r))
+					}
+				}
+			}
+		}
+	})
+
+	return true
+}
+
+func badPointerType(s string) bool {
+	return strings.HasPrefix(s, "C.CF") && strings.HasSuffix(s, "Ref")
+}
diff --git a/src/cmd/fix/cftype_test.go b/src/cmd/fix/cftype_test.go
new file mode 100644
index 0000000000..adaed2114f
--- /dev/null
+++ b/src/cmd/fix/cftype_test.go
@@ -0,0 +1,185 @@
+// Copyright 2017 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 main
+
+func init() {
+	addTestCases(cftypeTests, cftypefix)
+}
+
+var cftypeTests = []testCase{
+	{
+		Name: "cftype.localVariable",
+		In: `package main
+
+import "C"
+
+func f() {
+	var x C.CFTypeRef = nil
+	x = nil
+	x, x = nil, nil
+}
+`,
+		Out: `package main
+
+import "C"
+
+func f() {
+	var x C.CFTypeRef = 0
+	x = 0
+	x, x = 0, 0
+}
+`,
+	},
+	{
+		Name: "cftype.globalVariable",
+		In: `package main
+
+import "C"
+
+var x C.CFTypeRef = nil
+
+func f() {
+	x = nil
+}
+`,
+		Out: `package main
+
+import "C"
+
+var x C.CFTypeRef = 0
+
+func f() {
+	x = 0
+}
+`,
+	},
+	{
+		Name: "cftype.EqualArgument",
+		In: `package main
+
+import "C"
+
+var x C.CFTypeRef
+var y = x == nil
+var z = x != nil
+`,
+		Out: `package main
+
+import "C"
+
+var x C.CFTypeRef
+var y = x == 0
+var z = x != 0
+`,
+	},
+	{
+		Name: "cftype.StructField",
+		In: `package main
+
+import "C"
+
+type T struct {
+	x C.CFTypeRef
+}
+
+var t = T{x: nil}
+`,
+		Out: `package main
+
+import "C"
+
+type T struct {
+	x C.CFTypeRef
+}
+
+var t = T{x: 0}
+`,
+	},
+	{
+		Name: "cftype.FunctionArgument",
+		In: `package main
+
+import "C"
+
+func f(x C.CFTypeRef) {
+}
+
+func g() {
+	f(nil)
+}
+`,
+		Out: `package main
+
+import "C"
+
+func f(x C.CFTypeRef) {
+}
+
+func g() {
+	f(0)
+}
+`,
+	},
+	{
+		Name: "cftype.ArrayElement",
+		In: `package main
+
+import "C"
+
+var x = [3]C.CFTypeRef{nil, nil, nil}
+`,
+		Out: `package main
+
+import "C"
+
+var x = [3]C.CFTypeRef{0, 0, 0}
+`,
+	},
+	{
+		Name: "cftype.SliceElement",
+		In: `package main
+
+import "C"
+
+var x = []C.CFTypeRef{nil, nil, nil}
+`,
+		Out: `package main
+
+import "C"
+
+var x = []C.CFTypeRef{0, 0, 0}
+`,
+	},
+	{
+		Name: "cftype.MapKey",
+		In: `package main
+
+import "C"
+
+var x = map[C.CFTypeRef]int{nil: 0}
+`,
+		Out: `package main
+
+import "C"
+
+var x = map[C.CFTypeRef]int{0: 0}
+`,
+	},
+	{
+		Name: "cftype.MapValue",
+		In: `package main
+
+import "C"
+
+var x = map[int]C.CFTypeRef{0: nil}
+`,
+		Out: `package main
+
+import "C"
+
+var x = map[int]C.CFTypeRef{0: 0}
+`,
+	},
+}
diff --git a/src/cmd/fix/typecheck.go b/src/cmd/fix/typecheck.go
index 0352c49db0..58d915869d 100644
--- a/src/cmd/fix/typecheck.go
+++ b/src/cmd/fix/typecheck.go
@@ -498,6 +498,50 @@ func typecheck1(cfg *TypeConfig, f interface{}, typeof map[interface{}]string, a
 			// T{...} has type T.
 			typeof[n] = gofmt(n.Type)
 
+			// Propagate types down to values used in the composite literal.
+			t := expand(typeof[n])
+			if strings.HasPrefix(t, "[") { // array or slice
+				// Lazy: assume there are no nested [] in the array length.
+				if i := strings.Index(t, "]"); i >= 0 {
+					et := t[i+1:]
+					for _, e := range n.Elts {
+						if kv, ok := e.(*ast.KeyValueExpr); ok {
+							e = kv.Value
+						}
+						if typeof[e] == "" {
+							typeof[e] = et
+						}
+					}
+				}
+			}
+			if strings.HasPrefix(t, "map[") { // map
+				// Lazy: assume there are no nested [] in the map key type.
+				if i := strings.Index(t, "]"); i >= 0 {
+					kt, vt := t[4:i], t[i+1:]
+					for _, e := range n.Elts {
+						if kv, ok := e.(*ast.KeyValueExpr); ok {
+							if typeof[kv.Key] == "" {
+								typeof[kv.Key] = kt
+							}
+							if typeof[kv.Value] == "" {
+								typeof[kv.Value] = vt
+							}
+						}
+					}
+				}
+			}
+			if typ := cfg.Type[t]; typ != nil && len(typ.Field) > 0 { // struct
+				for _, e := range n.Elts {
+					if kv, ok := e.(*ast.KeyValueExpr); ok {
+						if ft := typ.Field[fmt.Sprintf("%s", kv.Key)]; ft != "" {
+							if typeof[kv.Value] == "" {
+								typeof[kv.Value] = ft
+							}
+						}
+					}
+				}
+			}
+
 		case *ast.ParenExpr:
 			// (x) has type of x.
 			typeof[n] = typeof[n.X]
@@ -579,6 +623,18 @@ func typecheck1(cfg *TypeConfig, f interface{}, typeof map[interface{}]string, a
 					set(res[i], t[i], false)
 				}
 			}
+
+		case *ast.BinaryExpr:
+			// Propagate types across binary ops that require two args of the same type.
+			switch n.Op {
+			case token.EQL, token.NEQ: // TODO: more cases. This is enough for the cftype fix.
+				if typeof[n.X] != "" && typeof[n.Y] == "" {
+					typeof[n.Y] = typeof[n.X]
+				}
+				if typeof[n.X] == "" && typeof[n.Y] != "" {
+					typeof[n.X] = typeof[n.Y]
+				}
+			}
 		}
 	}
 	walkBeforeAfter(f, before, after)