cgo: bug fixes

* Add documentation about array arguments.  Fixes issue 1125.
* Do not interpret x, y := z, w as special errno form.  Fixes issue 952.
* Fix nested Go calls (brainman).  Fixes issue 907.

R=r
CC=golang-dev
https://golang.org/cl/2214044

misc/cgo/stdio/test.go

@@ -19,6 +19,13 @@ enum {
 	Enum1 = 1,
 	Enum2 = 2,
 };
+
+typedef unsigned char uuid_t[20];
+
+void uuid_generate(uuid_t x) {
+	x[0] = 0;
+}
+
 */
 import "C"
 import (
@@ -30,6 +37,11 @@ const EINVAL = C.EINVAL /* test #define */
 
 var KILO = C.KILO
 
+func uuidgen() {
+	var uuid C.uuid_t
+	C.uuid_generate(&uuid[0])
+}
+
 func Size(name string) (int64, os.Error) {
 	var st C.struct_stat
 	p := C.CString(name)
@@ -73,10 +85,20 @@ func TestErrno() {
 	n, err := Strtol("asdf", 123)
 	if n != 0 || err != os.EINVAL {
 		println("Strtol: ", n, err)
-		panic("bad atoi2")
+		panic("bad strtol")
 	}
 }
 
+func TestMultipleAssign() {
+	p := C.CString("123")
+	n, m := C.strtol(p, nil, 345), C.strtol(p, nil, 10)
+	if n != 0 || m != 234 {
+		println("Strtol x2: ", n, m)
+		panic("bad strtol x2")
+	}
+	C.free(unsafe.Pointer(p))
+}
+
 var (
 	uint  = (C.uint)(0)
 	ulong C.ulong

src/cmd/cgo/ast.go

@@ -314,7 +314,7 @@ func (f *File) walk(x interface{}, context string, visit func(*File, interface{}
 		f.walk(&n.X, "expr", visit)
 	case *ast.AssignStmt:
 		f.walk(n.Lhs, "expr", visit)
-		if len(n.Lhs) == 2 {
+		if len(n.Lhs) == 2 && len(n.Rhs) == 1 {
 			f.walk(n.Rhs, "as2", visit)
 		} else {
 			f.walk(n.Rhs, "expr", visit)

src/cmd/cgo/doc.go

@@ -27,6 +27,12 @@ C identifiers or field names that are keywords in Go can be
 accessed by prefixing them with an underscore: if x points at
 a C struct with a field named "type", x._type accesses the field.
 
+The standard C numeric types are available under the names
+C.char, C.schar (signed char), C.uchar (unsigned char),
+C.short, C.ushort (unsigned short), C.int, C.uint (unsigned int),
+C.long, C.ulong (unsigned long), C.longlong (long long),
+C.ulonglong (unsigned long long), C.float, C.double.
+
 To access a struct, union, or enum type directly, prefix it with
 struct_, union_, or enum_, as in C.struct_stat.
 
@@ -36,6 +42,12 @@ C errno variable as an os.Error.  For example:
 
 	n, err := C.atoi("abc")
 
+In C, a function argument written as a fixed size array
+actually requires a pointer to the first element of the array.
+C compilers are aware of this calling convention and adjust
+the call accordingly, but Go cannot.  In Go, you must pass
+the pointer to the first element explicitly: C.f(&x[0]).
+
 Cgo transforms the input file into four output files: two Go source
 files, a C file for 6c (or 8c or 5c), and a C file for gcc.
 

src/pkg/runtime/cgocall.c

@@ -53,16 +53,16 @@ cgocall(void (*fn)(void*), void *arg)
 void
 cgocallback(void (*fn)(void), void *arg, int32 argsize)
 {
-	Gobuf oldsched;
+	Gobuf oldsched, oldg1sched;
 	G *g1;
 	void *sp;
 
 	if(g != m->g0)
 		throw("bad g in cgocallback");
 
-	oldsched = m->sched;
-
 	g1 = m->curg;
+	oldsched = m->sched;
+	oldg1sched = g1->sched;
 
 	startcgocallback(g1);
 
@@ -78,6 +78,7 @@ cgocallback(void (*fn)(void), void *arg, int32 argsize)
 	endcgocallback(g1);
 
 	m->sched = oldsched;
+	g1->sched = oldg1sched;
 }
 
 void