go/parser: if and switch statements still can have empty init statements

This is a fix for the overly aggressive CL 4173075.
Ran all tests.

R=r, rsc
CC=golang-dev
https://golang.org/cl/4203041

src/pkg/go/parser/parser.go

@@ -1339,13 +1339,18 @@ func (p *parser) parseIfStmt() *ast.IfStmt {
 	{
 		prevLev := p.exprLev
 		p.exprLev = -1
-		s = p.parseSimpleStmt(false)
 		if p.tok == token.SEMICOLON {
 			p.next()
 			x = p.parseExpr()
 		} else {
-			x = p.makeExpr(s)
-			s = nil
+			s = p.parseSimpleStmt(false)
+			if p.tok == token.SEMICOLON {
+				p.next()
+				x = p.parseExpr()
+			} else {
+				x = p.makeExpr(s)
+				s = nil
+			}
 		}
 		p.exprLev = prevLev
 	}
@@ -1447,7 +1452,9 @@ func (p *parser) parseSwitchStmt() ast.Stmt {
 	if p.tok != token.LBRACE {
 		prevLev := p.exprLev
 		p.exprLev = -1
-		s2 = p.parseSimpleStmt(false)
+		if p.tok != token.SEMICOLON {
+			s2 = p.parseSimpleStmt(false)
+		}
 		if p.tok == token.SEMICOLON {
 			p.next()
 			s1 = s2
@@ -1580,7 +1587,6 @@ func (p *parser) parseForStmt() ast.Stmt {
 	if p.tok != token.LBRACE {
 		prevLev := p.exprLev
 		p.exprLev = -1
-
 		if p.tok != token.SEMICOLON {
 			s2 = p.parseSimpleStmt(false)
 		}
@@ -1596,7 +1602,6 @@ func (p *parser) parseForStmt() ast.Stmt {
 				s3 = p.parseSimpleStmt(false)
 			}
 		}
-
 		p.exprLev = prevLev
 	}
 

src/pkg/go/parser/parser_test.go

@@ -19,6 +19,8 @@ var illegalInputs = []interface{}{
 	[]byte(nil),
 	"foo!",
 	`package p; func f() { if /* should have condition */ {} };`,
+	`package p; func f() { if ; /* should have condition */ {} };`,
+	`package p; func f() { if f(); /* should have condition */ {} };`,
 }
 
 
@@ -33,21 +35,23 @@ func TestParseIllegalInputs(t *testing.T) {
 
 
 var validPrograms = []interface{}{
-	"package main\n",
-	`package main;`,
-	`package main; import "fmt"; func main() { fmt.Println("Hello, World!") };`,
-	`package main; func main() { if f(T{}) {} };`,
-	`package main; func main() { _ = (<-chan int)(x) };`,
-	`package main; func main() { _ = (<-chan <-chan int)(x) };`,
-	`package main; func f(func() func() func());`,
-	`package main; func f(...T);`,
-	`package main; func f(float, ...int);`,
-	`package main; func f(x int, a ...int) { f(0, a...); f(1, a...,) };`,
-	`package main; type T []int; var a []bool; func f() { if a[T{42}[0]] {} };`,
-	`package main; type T []int; func g(int) bool { return true }; func f() { if g(T{42}[0]) {} };`,
-	`package main; type T []int; func f() { for _ = range []int{T{42}[0]} {} };`,
-	`package main; var a = T{{1, 2}, {3, 4}}`,
-	`package main; func f() { select { case <- c: case c <- d: case c <- <- d: case <-c <- d: } };`,
+	"package p\n",
+	`package p;`,
+	`package p; import "fmt"; func f() { fmt.Println("Hello, World!") };`,
+	`package p; func f() { if f(T{}) {} };`,
+	`package p; func f() { _ = (<-chan int)(x) };`,
+	`package p; func f() { _ = (<-chan <-chan int)(x) };`,
+	`package p; func f(func() func() func());`,
+	`package p; func f(...T);`,
+	`package p; func f(float, ...int);`,
+	`package p; func f(x int, a ...int) { f(0, a...); f(1, a...,) };`,
+	`package p; type T []int; var a []bool; func f() { if a[T{42}[0]] {} };`,
+	`package p; type T []int; func g(int) bool { return true }; func f() { if g(T{42}[0]) {} };`,
+	`package p; type T []int; func f() { for _ = range []int{T{42}[0]} {} };`,
+	`package p; var a = T{{1, 2}, {3, 4}}`,
+	`package p; func f() { select { case <- c: case c <- d: case c <- <- d: case <-c <- d: } };`,
+	`package p; func f() { if ; true {} };`,
+	`package p; func f() { switch ; {} };`,
 }
 
 

src/pkg/go/printer/testdata/statements.golden

@@ -12,10 +12,16 @@ func use(x interface{})	{}
 func _() {
 	if true {
 	}
+	if true {
+	}	// no semicolon printed
 	if expr {
 	}
 	if expr {
+	}	// no semicolon printed
+	if expr {
 	}	// no parens printed
+	if expr {
+	}	// no semicolon and parens printed
 	if x := expr; true {
 		use(x)
 	}
@@ -29,10 +35,16 @@ func _() {
 func _() {
 	switch {
 	}
+	switch {
+	}	// no semicolon printed
 	switch expr {
 	}
 	switch expr {
+	}	// no semicolon printed
+	switch expr {
 	}	// no parens printed
+	switch expr {
+	}	// no semicolon and parens printed
 	switch x := expr; {
 	default:
 		use(

src/pkg/go/printer/testdata/statements.input

@@ -11,9 +11,12 @@ func use(x interface{}) {}
 // Formatting of if-statement headers.
 func _() {
 	if true {}
+	if; true {}  // no semicolon printed
 	if expr{}
+	if;expr{}  // no semicolon printed
 	if (expr){}  // no parens printed
-	if x:=expr; true {
+	if;((expr)){}  // no semicolon and parens printed
+	if x:=expr;true{
 	use(x)}
 	if x:=expr; expr {use(x)}
 }
@@ -22,8 +25,11 @@ func _() {
 // Formatting of switch-statement headers.
 func _() {
 	switch {}
+	switch;{}  // no semicolon printed
 	switch expr {}
+	switch;expr{}  // no semicolon printed
 	switch (expr) {}  // no parens printed
+	switch;((expr)){}  // no semicolon and parens printed
 	switch x := expr; { default:use(
 x)
 	}
@@ -112,7 +118,7 @@ func _() {
 	if (((x))) {}
 	if ([]T{}) {}
 	if (([]T{})) {}
-	if (((([]T{})))) {}
+	if ; (((([]T{})))) {}
 
 	for (x) {}
 	for (((x))) {}
@@ -123,21 +129,21 @@ func _() {
 	switch (x) {}
 	switch (((x))) {}
 	switch ([]T{}) {}
-	switch (((([]T{})))) {}
+	switch ; (((([]T{})))) {}
 
 	for _ = range ((([]T{T{42}}))) {}
 
 	// leave parentheses - composite literals start with a type name
 	if (T{}) {}
 	if ((T{})) {}
-	if ((((T{})))) {}
+	if ; ((((T{})))) {}
 
 	for (T{}) {}
 	for ((T{})) {}
 	for ; ((((T{})))) ; {}
 
 	switch (T{}) {}
-	switch ((((T{})))) {}
+	switch ; ((((T{})))) {}
 
 	for _ = range (((T1{T{42}}))) {}