cmd/compile/internal/types2: make ptrRecv a method hasPtrRecv of Func

Reading the Func.hasPtrRecv field directly (without consulting a
possibly existing signature) caused some issues in an earlier CL.
The function ptrRecv (in lookup.go) does the right thing but is
not easily discoverable.

Rename ptrRecv to hasPtrRecv and make it a method of Func; rename
Func.hasPtrRecv field to Func.hasPtrRecv_ to avoid name collisions.
Make it clear in field comment that it must not be read through the
hasPtrRecv method.

Change-Id: Ida9856c4789e499538eb34377be781655958fd5b
Reviewed-on: https://go-review.googlesource.com/c/go/+/351310
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/lookup.go

@@ -216,7 +216,7 @@ func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (o
 			//        is shorthand for (&x).m()".
 			if f, _ := obj.(*Func); f != nil {
 				// determine if method has a pointer receiver
-				hasPtrRecv := tpar == nil && ptrRecv(f)
+				hasPtrRecv := tpar == nil && f.hasPtrRecv()
 				if hasPtrRecv && !indirect && !addressable {
 					return nil, nil, true // pointer/addressable receiver required
 				}
@@ -474,22 +474,3 @@ func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
 	}
 	return -1, nil
 }
-
-// ptrRecv reports whether the receiver is of the form *T.
-func ptrRecv(f *Func) bool {
-	// If a method's receiver type is set, use that as the source of truth for the receiver.
-	// Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
-	// signature. We may reach here before the signature is fully set up: we must explicitly
-	// check if the receiver is set (we cannot just look for non-nil f.typ).
-	if sig, _ := f.typ.(*Signature); sig != nil && sig.recv != nil {
-		_, isPtr := deref(sig.recv.typ)
-		return isPtr
-	}
-
-	// If a method's type is not set it may be a method/function that is:
-	// 1) client-supplied (via NewFunc with no signature), or
-	// 2) internally created but not yet type-checked.
-	// For case 1) we can't do anything; the client must know what they are doing.
-	// For case 2) we can use the information gathered by the resolver.
-	return f.hasPtrRecv
-}

src/cmd/compile/internal/types2/named.go

@@ -255,7 +255,7 @@ func expandNamed(env *Environment, n *Named, instPos syntax.Pos) (tparams *TypeP
 			// During type checking origm may not have a fully set up type, so defer
 			// instantiation of its signature until later.
 			m := NewFunc(origm.pos, origm.pkg, origm.name, nil)
-			m.hasPtrRecv = ptrRecv(origm)
+			m.hasPtrRecv_ = origm.hasPtrRecv()
 			// Setting instRecv here allows us to complete later (we need the
 			// instRecv to get targs and the original method).
 			m.instRecv = n
@@ -314,7 +314,7 @@ func (check *Checker) completeMethod(env *Environment, m *Func) {
 		sig = &copy
 	}
 	var rtyp Type
-	if ptrRecv(m) {
+	if m.hasPtrRecv() {
 		rtyp = NewPointer(rbase)
 	} else {
 		rtyp = rbase

src/cmd/compile/internal/types2/object.go

@@ -363,8 +363,8 @@ func (*Var) isDependency() {} // a variable may be a dependency of an initializa
 // An abstract method may belong to many interfaces due to embedding.
 type Func struct {
 	object
-	instRecv   *Named // if non-nil, the receiver type for an incomplete instance method
-	hasPtrRecv bool   // only valid for methods that don't have a type yet
+	instRecv    *Named // if non-nil, the receiver type for an incomplete instance method
+	hasPtrRecv_ bool   // only valid for methods that don't have a type yet; use hasPtrRecv() to read
 }
 
 // NewFunc returns a new function with the given signature, representing
@@ -389,6 +389,25 @@ func (obj *Func) FullName() string {
 // Scope returns the scope of the function's body block.
 func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
 
+// hasPtrRecv reports whether the receiver is of the form *T for the given method obj.
+func (obj *Func) hasPtrRecv() bool {
+	// If a method's receiver type is set, use that as the source of truth for the receiver.
+	// Caution: Checker.funcDecl (decl.go) marks a function by setting its type to an empty
+	// signature. We may reach here before the signature is fully set up: we must explicitly
+	// check if the receiver is set (we cannot just look for non-nil obj.typ).
+	if sig, _ := obj.typ.(*Signature); sig != nil && sig.recv != nil {
+		_, isPtr := deref(sig.recv.typ)
+		return isPtr
+	}
+
+	// If a method's type is not set it may be a method/function that is:
+	// 1) client-supplied (via NewFunc with no signature), or
+	// 2) internally created but not yet type-checked.
+	// For case 1) we can't do anything; the client must know what they are doing.
+	// For case 2) we can use the information gathered by the resolver.
+	return obj.hasPtrRecv_
+}
+
 func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
 
 // A Label represents a declared label.

src/cmd/compile/internal/types2/resolver.go

@@ -509,7 +509,7 @@ func (check *Checker) collectObjects() {
 			// Determine the receiver base type and associate m with it.
 			ptr, base := check.resolveBaseTypeName(m.ptr, m.recv)
 			if base != nil {
-				m.obj.hasPtrRecv = ptr
+				m.obj.hasPtrRecv_ = ptr
 				check.methods[base] = append(check.methods[base], m.obj)
 			}
 		}