cmd/compile/internal/syntax: use BadExpr instead of fake CallExpr in bad go/defer

If the go/defer syntax is bad, using a fake CallExpr may produce
a follow-on error in the type checker. Instead store a BadExpr
in the syntax tree (since an error has already been reported).

Adjust various tests.

For #54511.

Change-Id: Ib2d25f8eab7d5745275188d83d11620cad6ef47c
Reviewed-on: https://go-review.googlesource.com/c/go/+/425675
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>

src/cmd/compile/internal/syntax/nodes.go

@@ -385,7 +385,7 @@ type (
 
 	CallStmt struct {
 		Tok  token // Go or Defer
-		Call *CallExpr
+		Call Expr
 		stmt
 	}
 

src/cmd/compile/internal/syntax/parser.go

@@ -951,16 +951,21 @@ func (p *parser) callStmt() *CallStmt {
 		x = t
 	}
 
-	cx, ok := x.(*CallExpr)
-	if !ok {
-		p.errorAt(x.Pos(), fmt.Sprintf("expression in %s must be function call", s.Tok))
-		// already progressed, no need to advance
-		cx = new(CallExpr)
-		cx.pos = x.Pos()
-		cx.Fun = x // assume common error of missing parentheses (function invocation)
+	// TODO(gri) Now that we don't store a CallExpr in a CallStmt anymore
+	//           we might as well leave this check to the type checker.
+	//           Adjust this here and in go/parser eventually.
+	if _, ok := x.(*CallExpr); !ok {
+		// only report an error if it's a new one
+		if bad, ok := x.(*BadExpr); !ok {
+			p.errorAt(x.Pos(), fmt.Sprintf("expression in %s must be function call", s.Tok))
+			// already progressed, no need to advance
+			bad = new(BadExpr)
+			bad.pos = x.Pos()
+			x = bad
+		}
 	}
 
-	s.Call = cx
+	s.Call = x
 	return s
 }
 

src/cmd/compile/internal/syntax/testdata/issue20789.go

@@ -6,4 +6,4 @@
 // Line 9 must end in EOF for this test (no newline).
 
 package e
-func([<-chan<-[func /* ERROR unexpected u */ u){go /* ERROR must be function call */
+func([<-chan<-[func /* ERROR unexpected u */ u){go

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

@@ -165,7 +165,7 @@ func (check *Checker) closeScope() {
 	check.scope = check.scope.Parent()
 }
 
-func (check *Checker) suspendedCall(keyword string, call *syntax.CallExpr) {
+func (check *Checker) suspendedCall(keyword string, call syntax.Expr) {
 	var x operand
 	var msg string
 	switch check.rawExpr(&x, call, nil, false) {

src/cmd/compile/internal/types2/testdata/check/stmt0.go

@@ -229,7 +229,7 @@ func selects() {
 }
 
 func gos() {
-	go 1 /* ERROR must be function call */ /* ERROR cannot call non-function */
+	go 1 /* ERROR must be function call */
 	go int /* ERROR "go requires function call, not conversion" */ (0)
 	go gos()
 	var c chan int
@@ -238,7 +238,7 @@ func gos() {
 }
 
 func defers() {
-	defer 1 /* ERROR must be function call */ /* ERROR cannot call non-function */
+	defer 1 /* ERROR must be function call */
 	defer int /* ERROR "defer requires function call, not conversion" */ (0)
 	defer defers()
 	var c chan int

test/fixedbugs/issue20789.go

@@ -10,4 +10,4 @@
 // there yet, so put it here for now. See also #20800.)
 
 package e
-func([<-chan<-[func u){go // ERROR "unexpected u", ERROR "must be function call"
+func([<-chan<-[func u){go // ERROR "unexpected u"

test/fixedbugs/issue23586.go

@@ -11,13 +11,15 @@
 
 package p
 
+// TODO(gri) The "not used" errors should not be reported.
+
 import (
-	"fmt"
-	"math"
+	"fmt"  // ERROR "imported and not used"
+	"math" // ERROR "imported and not used"
 )
 
 func f() {
-	var i int
+	var i int // ERROR "i declared but not used"
 	defer func() { fmt.Println() } // ERROR "must be function call"
 	go func() { _ = math.Sin(0) }  // ERROR "must be function call"
 	go func() { _ = i}             // ERROR "must be function call"