From a7a3fe72386df56d6bf6cd83fe346e1c72cf998a Mon Sep 17 00:00:00 2001
From: Daniel Morsing <daniel.morsing@gmail.com>
Date: Sun, 21 Oct 2012 19:22:51 +0200
Subject: [PATCH] cmd/gc: Friendlier errors on oversized arrays.

Someone new to the language may not know the connection between ints and arrays, which was the only thing that the previous error told you anything about.

Fixes #4256.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6739048
---
 src/cmd/gc/const.c       | 40 +++++++++++++++++++++++++++++++---------
 src/cmd/gc/go.h          |  3 ++-
 src/cmd/gc/typecheck.c   |  6 ++++--
 test/fixedbugs/bug255.go |  2 +-
 4 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/src/cmd/gc/const.c b/src/cmd/gc/const.c
index e4c1a784ab5..5720efc8e92 100644
--- a/src/cmd/gc/const.c
+++ b/src/cmd/gc/const.c
@@ -348,13 +348,9 @@ toint(Val v)
 	return v;
 }
 
-void
-overflow(Val v, Type *t)
+int
+doesoverflow(Val v, Type *t)
 {
-	// v has already been converted
-	// to appropriate form for t.
-	if(t == T || t->etype == TIDEAL)
-		return;
 	switch(v.ctype) {
 	case CTINT:
 	case CTRUNE:
@@ -362,14 +358,14 @@ overflow(Val v, Type *t)
 			fatal("overflow: %T integer constant", t);
 		if(mpcmpfixfix(v.u.xval, minintval[t->etype]) < 0 ||
 		   mpcmpfixfix(v.u.xval, maxintval[t->etype]) > 0)
-			yyerror("constant %B overflows %T", v.u.xval, t);
+			return 1;
 		break;
 	case CTFLT:
 		if(!isfloat[t->etype])
 			fatal("overflow: %T floating-point constant", t);
 		if(mpcmpfltflt(v.u.fval, minfltval[t->etype]) <= 0 ||
 		   mpcmpfltflt(v.u.fval, maxfltval[t->etype]) >= 0)
-			yyerror("constant %#F overflows %T", v.u.fval, t);
+			return 1;
 		break;
 	case CTCPLX:
 		if(!iscomplex[t->etype])
@@ -378,7 +374,33 @@ overflow(Val v, Type *t)
 		   mpcmpfltflt(&v.u.cval->real, maxfltval[t->etype]) >= 0 ||
 		   mpcmpfltflt(&v.u.cval->imag, minfltval[t->etype]) <= 0 ||
 		   mpcmpfltflt(&v.u.cval->imag, maxfltval[t->etype]) >= 0)
-			yyerror("constant %#F overflows %T", v.u.fval, t);
+			return 1;
+		break;
+	}
+	return 0;
+}
+
+void
+overflow(Val v, Type *t)
+{
+	// v has already been converted
+	// to appropriate form for t.
+	if(t == T || t->etype == TIDEAL)
+		return;
+
+	if(!doesoverflow(v, t))
+		return;
+
+	switch(v.ctype) {
+	case CTINT:
+	case CTRUNE:
+		yyerror("constant %B overflows %T", v.u.xval, t);
+		break;
+	case CTFLT:
+		yyerror("constant %#F overflows %T", v.u.fval, t);
+		break;
+	case CTCPLX:
+		yyerror("constant %#F overflows %T", v.u.fval, t);
 		break;
 	}
 }
diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index eb2345d6da3..2fa6d95bef1 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -178,7 +178,7 @@ struct	Type
 	Strlit*	note;		// literal string annotation
 
 	// TARRAY
-	int32	bound;		// negative is dynamic array
+	vlong	bound;		// negative is dynamic array
 
 	int32	maplineno;	// first use of TFORW as map key
 	int32	embedlineno;	// first use of TFORW as embedded type
@@ -977,6 +977,7 @@ int	isconst(Node *n, int ct);
 Node*	nodcplxlit(Val r, Val i);
 Node*	nodlit(Val v);
 long	nonnegconst(Node *n);
+int	doesoverflow(Val v, Type *t);
 void	overflow(Val v, Type *t);
 int	smallintconst(Node *n);
 Val	toint(Val v);
diff --git a/src/cmd/gc/typecheck.c b/src/cmd/gc/typecheck.c
index ebc43e75983..9869d560cb9 100644
--- a/src/cmd/gc/typecheck.c
+++ b/src/cmd/gc/typecheck.c
@@ -390,8 +390,10 @@ reswitch:
 			if(t->bound < 0) {
 				yyerror("array bound must be non-negative");
 				goto error;
-			} else
-				overflow(v, types[TINT]);
+			} else if(doesoverflow(v, types[TINT])) {
+				yyerror("array bound is too large"); 
+				goto error;
+			}
 		}
 		typecheck(&r, Etype);
 		if(r->type == T)
diff --git a/test/fixedbugs/bug255.go b/test/fixedbugs/bug255.go
index dbd41cc6ab3..acf4f23910d 100644
--- a/test/fixedbugs/bug255.go
+++ b/test/fixedbugs/bug255.go
@@ -12,4 +12,4 @@ var c [1.5]int	// ERROR "truncated"
 var d ["abc"]int	// ERROR "invalid array bound|not numeric"
 var e [nil]int	// ERROR "invalid array bound|not numeric"
 var f [e]int	// ERROR "invalid array bound|not constant"
-var g [1<<65]int	// ERROR "overflows"
+var g [1<<65]int	// ERROR "array bound is too large|overflows"