go/ir: don't treat _ specially in Prog.{Func,Const,Var}Value

Because of a (long-since fixed) bug in go/types, the Program
accessors that accept types.Objects didn't work for blank-named
objects. This created an edge case that needed to be skipped
in client code: FuncValue("_") would return nil, for example,
even thought there's no reason clients shouldn't be able to
analyze the bodies of blank functions.

This change inserts all objects, regardless of name, into the
Package.objects map to eliminate this edge case. (Of course,
declarations must still have non-blank names to appear in the
Members mapping.)

(cherry picked from commit 942d9acc1ecb8b0ec51d6660adb17ee80ec47090 in
x/tools)

Co-authored-by: Dominik Honnef <dominik@honnef.co>

go/ir/create.go

@@ -58,9 +58,11 @@ func memberFromObject(pkg *Package, obj types.Object, syntax ast.Node, goversion
 		}
 
 	case *types.TypeName:
-		pkg.Members[name] = &Type{
-			object: obj,
-			pkg:    pkg,
+		if name != "_" {
+			pkg.Members[name] = &Type{
+				object: obj,
+				pkg:    pkg,
+			}
 		}
 
 	case *types.Const:
@@ -70,7 +72,9 @@ func memberFromObject(pkg *Package, obj types.Object, syntax ast.Node, goversion
 			pkg:    pkg,
 		}
 		pkg.values[obj] = c.Value
-		pkg.Members[name] = c
+		if name != "_" {
+			pkg.Members[name] = c
+		}
 
 	case *types.Var:
 		g := &Global{
@@ -80,7 +84,9 @@ func memberFromObject(pkg *Package, obj types.Object, syntax ast.Node, goversion
 			typ:    types.NewPointer(obj.Type()), // address
 		}
 		pkg.values[obj] = g
-		pkg.Members[name] = g
+		if name != "_" {
+			pkg.Members[name] = g
+		}
 
 	case *types.Func:
 		sig := obj.Type().(*types.Signature)
@@ -114,7 +120,7 @@ func memberFromObject(pkg *Package, obj types.Object, syntax ast.Node, goversion
 
 		pkg.values[obj] = fn
 		pkg.Functions = append(pkg.Functions, fn)
-		if sig.Recv() == nil {
+		if name != "_" && sig.Recv() == nil {
 			pkg.Members[name] = fn // package-level function
 		}
 
@@ -133,9 +139,7 @@ func membersFromDecl(pkg *Package, decl ast.Decl, goversion string) {
 		case token.CONST:
 			for _, spec := range decl.Specs {
 				for _, id := range spec.(*ast.ValueSpec).Names {
-					if !isBlankIdent(id) {
-						memberFromObject(pkg, pkg.info.Defs[id], nil, "")
-					}
+					memberFromObject(pkg, pkg.info.Defs[id], nil, "")
 				}
 			}
 
@@ -145,26 +149,20 @@ func membersFromDecl(pkg *Package, decl ast.Decl, goversion string) {
 					pkg.initVersion[rhs] = goversion
 				}
 				for _, id := range spec.(*ast.ValueSpec).Names {
-					if !isBlankIdent(id) {
-						memberFromObject(pkg, pkg.info.Defs[id], spec, goversion)
-					}
+					memberFromObject(pkg, pkg.info.Defs[id], spec, goversion)
 				}
 			}
 
 		case token.TYPE:
 			for _, spec := range decl.Specs {
 				id := spec.(*ast.TypeSpec).Name
-				if !isBlankIdent(id) {
-					memberFromObject(pkg, pkg.info.Defs[id], nil, "")
-				}
+				memberFromObject(pkg, pkg.info.Defs[id], nil, "")
 			}
 		}
 
 	case *ast.FuncDecl:
 		id := decl.Name
-		if !isBlankIdent(id) {
-			memberFromObject(pkg, pkg.info.Defs[id], decl, goversion)
-		}
+		memberFromObject(pkg, pkg.info.Defs[id], decl, goversion)
 	}
 }
 

internal/passes/buildir/buildir.go

@@ -35,7 +35,7 @@ var Analyzer = &analysis.Analyzer{
 }
 
 // IR provides intermediate representation for all the
-// non-blank source functions in the current package.
+// source functions in the current package.
 type IR struct {
 	Pkg      *ir.Package
 	SrcFuncs []*ir.Function

internal/passes/buildir/buildir_test.go

@@ -18,7 +18,7 @@ func Test(t *testing.T) {
 
 	irinfo := result.(*buildir.IR)
 	got := fmt.Sprint(irinfo.SrcFuncs)
-	want := `[a.init a.Fib (a.T).fib]`
+	want := `[a.init a.Fib (a.T).fib a._ a._]`
 	if got != want {
 		t.Errorf("IR.SrcFuncs = %s, want %s", got, want)
 		for _, f := range irinfo.SrcFuncs {

internal/passes/buildir/testdata/src/a/a.go

@@ -14,3 +14,7 @@ func (T) fib(x int) int { return Fib(x) }
 func _() {
 	print("hi")
 }
+
+func _() {
+	print("hi")
+}