gc: complex(0)

Fixes #1232.

R=ken2
CC=golang-dev
https://golang.org/cl/3621041

src/cmd/gc/const.c

@@ -202,8 +202,6 @@ convlit1(Node **np, Type *t, int explicit)
  goto bad;
  case CTFLT:
  case CTINT:
- if(explicit)
- goto bad;
  n->val = tocplx(n->val);
  break;
  case CTCPLX:
@@ -300,7 +298,7 @@ toflt(Val v)
  f = mal(sizeof(*f));
  mpmovefltflt(f, &v.u.cval->real);
  if(mpcmpfltc(&v.u.cval->imag, 0) != 0)
- yyerror("constant %#F truncated to real", v.u.fval);
+ yyerror("constant %#F%+#Fi truncated to real", &v.u.cval->real, &v.u.cval->imag);
  v.ctype = CTFLT;
  v.u.fval = f;
  break;
@@ -324,9 +322,9 @@ toint(Val v)
  case CTCPLX:
  i = mal(sizeof(*i));
  if(mpmovefltfix(i, &v.u.cval->real) < 0)
- yyerror("constant %#F truncated to integer", v.u.fval);
+ yyerror("constant %#F%+#Fi truncated to integer", &v.u.cval->real, &v.u.cval->imag);
  if(mpcmpfltc(&v.u.cval->imag, 0) != 0)
- yyerror("constant %#F truncated to real", v.u.fval);
+ yyerror("constant %#F%+#Fi truncated to real", &v.u.cval->real, &v.u.cval->imag);
  v.ctype = CTINT;
  v.u.xval = i;
  break;

src/cmd/gc/mparith1.c

@@ -475,6 +475,8 @@ Fconv(Fmt *fp)
  // for well in range, convert to double and use print's %g
  if(-900 < fvp->exp && fvp->exp < 900) {
  d = mpgetflt(fvp);
+ if(d >= 0 && (fp->flags & FmtSign))
+ fmtprint(fp, "+");
  return fmtprint(fp, "%g", d);
  }
  // TODO(rsc): for well out of range, print

test/cmplx.go

@@ -22,6 +22,7 @@ func main() {
  c64 = cmplx(f32, f32)
  c128 = cmplx(f64, f64)
 
+ _ = complex(0) // ok
  _ = cmplx(f, f32) // ERROR "cmplx"
  _ = cmplx(f, f64) // ERROR "cmplx"
  _ = cmplx(f32, f) // ERROR "cmplx"