cmd/gc: implement 'for range x {'

Fixes #6102.

LGTM=gri
R=ken, r, gri
CC=golang-codereviews
https://golang.org/cl/113120043

src/cmd/gc/esc.c

@@ -495,7 +495,7 @@ esc(EscState *e, Node *n, Node *up)
 
 	case ORANGE:
 		// Everything but fixed array is a dereference.
-		if(isfixedarray(n->type) && n->list->next)
+		if(isfixedarray(n->type) && n->list && n->list->next)
 			escassign(e, n->list->next->n, n->right);
 		break;
 

src/cmd/gc/fmt.c

@@ -880,7 +880,11 @@ stmtfmt(Fmt *f, Node *n)
 			fmtstrcpy(f, "for loop");
 			break;
 		}
-
+		
+		if(n->list == nil) {
+			fmtprint(f, "for range %N { %H }", n->right, n->nbody);
+			break;
+		}
 		fmtprint(f, "for %,H = range %N { %H }", n->list, n->right, n->nbody);
 		break;
 

src/cmd/gc/go.y

@@ -613,6 +613,11 @@ range_stmt:
 		$$->colas = 1;
 		colasdefn($1, $$);
 	}
+|	LRANGE expr
+	{
+		$$ = nod(ORANGE, N, $2);
+		$$->etype = 0; // := flag
+	}
 
 for_header:
 	osimple_stmt ';' osimple_stmt ';' osimple_stmt

src/cmd/gc/range.c

@@ -67,9 +67,11 @@ typecheckrange(Node *n)
 		yyerror("too many variables in range");
 	}
 
-	v1 = n->list->n;
+	v1 = N;
+	if(n->list)
+		v1 = n->list->n;
 	v2 = N;
-	if(n->list->next)
+	if(n->list && n->list->next)
 		v2 = n->list->next->n;
 
 	// this is not only a optimization but also a requirement in the spec.
@@ -77,14 +79,17 @@ typecheckrange(Node *n)
 	// clause is equivalent to the same clause with only the first variable
 	// present."
 	if(isblank(v2)) {
-		n->list = list1(v1);
+		if(v1 != N)
+			n->list = list1(v1);
 		v2 = N;
 	}
 
-	if(v1->defn == n)
-		v1->type = t1;
-	else if(v1->type != T && assignop(t1, v1->type, &why) == 0)
-		yyerror("cannot assign type %T to %lN in range%s", t1, v1, why);
+	if(v1) {
+		if(v1->defn == n)
+			v1->type = t1;
+		else if(v1->type != T && assignop(t1, v1->type, &why) == 0)
+			yyerror("cannot assign type %T to %lN in range%s", t1, v1, why);
+	}
 	if(v2) {
 		if(v2->defn == n)
 			v2->type = t2;
@@ -123,9 +128,11 @@ walkrange(Node *n)
 	a = n->right;
 	lno = setlineno(a);
 
-	v1 = n->list->n;
+	v1 = N;
+	if(n->list)
+		v1 = n->list->n;
 	v2 = N;
-	if(n->list->next && !isblank(n->list->next->n))
+	if(n->list && n->list->next && !isblank(n->list->next->n))
 		v2 = n->list->next->n;
 	// n->list has no meaning anymore, clear it
 	// to avoid erroneous processing by racewalk.
@@ -154,7 +161,9 @@ walkrange(Node *n)
 
 		n->ntest = nod(OLT, hv1, hn);
 		n->nincr = nod(OAS, hv1, nod(OADD, hv1, nodintconst(1)));
-		if(v2 == N)
+		if(v1 == N)
+			body = nil;
+		else if(v2 == N)
 			body = list1(nod(OAS, v1, hv1));
 		else {
 			a = nod(OAS2, N, N);
@@ -205,16 +214,18 @@ walkrange(Node *n)
 
 		key = nod(ODOT, hit, keyname);
 		key = nod(OIND, key, N);
-		if(v2 == N) {
-			a = nod(OAS, v1, key);
+		if(v1 == N)
+			body = nil;
+		else if(v2 == N) {
+			body = list1(nod(OAS, v1, key));
 		} else {
 			val = nod(ODOT, hit, valname);
 			val = nod(OIND, val, N);
 			a = nod(OAS2, N, N);
 			a->list = list(list1(v1), v2);
 			a->rlist = list(list1(key), val);
+			body = list1(a);
 		}
-		body = list1(a);
 		break;
 
 	case TCHAN:
@@ -223,6 +234,7 @@ walkrange(Node *n)
 		n->ntest = N;
 		
 		hv1 = temp(t->type);
+		hv1->typecheck = 1;
 		if(haspointers(t->type))
 			init = list(init, nod(OAS, hv1, N));
 		hb = temp(types[TBOOL]);
@@ -233,7 +245,10 @@ walkrange(Node *n)
 		a->list = list(list1(hv1), hb);
 		a->rlist = list1(nod(ORECV, ha, N));
 		n->ntest->ninit = list1(a);
-		body = list1(nod(OAS, v1, hv1));
+		if(v1 == N)
+			body = nil;
+		else
+			body = list1(nod(OAS, v1, hv1));
 		break;
 
 	case TSTRING:
@@ -257,7 +272,10 @@ walkrange(Node *n)
 		n->ntest = nod(ONE, hv1, nodintconst(0));
 		n->ntest->ninit = list(list1(nod(OAS, ohv1, hv1)), a);
 
-		body = list1(nod(OAS, v1, ohv1));
+		
+		body = nil;
+		if(v1 != N)
+			body = list1(nod(OAS, v1, ohv1));
 		if(v2 != N)
 			body = list(body, nod(OAS, v2, hv2));
 		break;

src/cmd/gc/yerr.h

@@ -20,16 +20,16 @@ static struct {
 	{32, ';',
 	"missing import path; require quoted string"},
 
-	{378, ';',
+	{380, ';',
 	"missing { after if clause"},
 
-	{399, ';',
+	{401, ';',
 	"missing { after switch clause"},
 
-	{238, ';',
+	{239, ';',
 	"missing { after for clause"},
 
-	{476, LBODY,
+	{478, LBODY,
 	"missing { after for clause"},
 
 	{22, '{',
@@ -47,33 +47,33 @@ static struct {
 	{37, ',',
 	"unexpected comma in channel type"},
 
-	{439, LELSE,
+	{441, LELSE,
 	"unexpected semicolon or newline before else"},
 
-	{258, ',',
+	{259, ',',
 	"name list not allowed in interface type"},
 
-	{238, LVAR,
+	{239, LVAR,
 	"var declaration not allowed in for initializer"},
 
 	{65, '{',
 	"unexpected { at end of statement"},
 
-	{377, '{',
+	{379, '{',
 	"unexpected { at end of statement"},
 	
 	{126, ';',
 	"argument to go/defer must be function call"},
 	
-	{426, ';',
+	{428, ';',
 	"need trailing comma before newline in composite literal"},
 	
-	{437, ';',
+	{439, ';',
 	"need trailing comma before newline in composite literal"},
 	
 	{113, LNAME,
 	"nested func not allowed"},
 
-	{645, ';',
+	{647, ';',
 	"else must be followed by if or statement block"}
 };

test/bench/shootout/chameneosredux.go

@@ -123,7 +123,7 @@ func pallmall(cols []int) {
 	fmt.Println(msg)
 	tot := 0
 	// wait for all results
-	for _ = range cols {
+	for range cols {
 		result := <-ended
 		tot += result.met
 		fmt.Printf("%v%v\n", result.met, spell(result.same, true))

test/chan/perm.go

@@ -56,6 +56,9 @@ func main() {
 	for _ = range cs {// ERROR "receive"
 	}
 
+	for range cs {// ERROR "receive"
+	}
+
 	close(c)
 	close(cs)
 	close(cr)  // ERROR "receive"

test/fixedbugs/bug173.go

@@ -18,4 +18,6 @@ func main() {
 	}
 	for _ = range t {
 	}
+	for range t {
+	}
 }

test/fixedbugs/bug406.go

@@ -14,6 +14,8 @@ type matrix struct {
 func (a matrix) equal() bool {
 	for _ = range a.e {
 	}
+	for range a.e {
+	}
 	return true
 }
 

test/range.go

@@ -32,6 +32,13 @@ func testchan() {
 		println("Wanted lowercase alphabet; got", s)
 		panic("fail")
 	}
+	n := 0
+	for range seq('a', 'z') {
+		n++
+	}
+	if n != 26 {
+		println("testchan wrong count", n, "want 26")
+	}
 }
 
 // test that range over slice only evaluates
@@ -87,6 +94,22 @@ func testslice1() {
 	}
 }
 
+func testslice2() {
+	n := 0
+	nmake = 0
+	for range makeslice() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makeslice", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makeslice", n)
+		panic("fail")
+	}
+}
+
 // test that range over array only evaluates
 // the expression after "range" once.
 
@@ -127,6 +150,22 @@ func testarray1() {
 	}
 }
 
+func testarray2() {
+	n := 0
+	nmake = 0
+	for range makearray() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makearray", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makearray", n)
+		panic("fail")
+	}
+}
+
 func makearrayptr() *[5]int {
 	nmake++
 	return &[5]int{1, 2, 3, 4, 5}
@@ -176,6 +215,22 @@ func testarrayptr1() {
 	}
 }
 
+func testarrayptr2() {
+	n := 0
+	nmake = 0
+	for range makearrayptr() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makearrayptr", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makearrayptr", n)
+		panic("fail")
+	}
+}
+
 // test that range over string only evaluates
 // the expression after "range" once.
 
@@ -216,6 +271,22 @@ func teststring1() {
 	}
 }
 
+func teststring2() {
+	n := 0
+	nmake = 0
+	for range makestring() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makestring", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makestring", n)
+		panic("fail")
+	}
+}
+
 // test that range over map only evaluates
 // the expression after "range" once.
 
@@ -256,6 +327,22 @@ func testmap1() {
 	}
 }
 
+func testmap2() {
+	n := 0
+	nmake = 0
+	for range makemap() {
+		n++
+	}
+	if nmake != 1 {
+		println("range called makemap", nmake, "times")
+		panic("fail")
+	}
+	if n != 5 {
+		println("wrong count ranging over makemap", n)
+		panic("fail")
+	}
+}
+
 // test that range evaluates the index and value expressions
 // exactly once per iteration.
 
@@ -298,13 +385,18 @@ func main() {
 	testchan()
 	testarray()
 	testarray1()
+	testarray2()
 	testarrayptr()
 	testarrayptr1()
+	testarrayptr2()
 	testslice()
 	testslice1()
+	testslice2()
 	teststring()
 	teststring1()
+	teststring2()
 	testmap()
 	testmap1()
+	testmap2()
 	testcalls()
 }

test/stress/maps.go

@@ -97,6 +97,8 @@ func (m intMap) Len() int { return len(m) }
 func (m intMap) RangeAll() {
 	for _ = range m {
 	}
+	for range m {
+	}
 }
 
 func stressMaps() {