From 23e62d169fce3e85b6df74a878d2911d74d6b168 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Wed, 20 May 2009 18:23:19 -0700
Subject: [PATCH] stricter interface conversion rule: i.(T) must have non-nil
 i.

R=ken
OCL=29136
CL=29136
---
 src/cmd/gc/builtin.c.boot |  1 +
 src/cmd/gc/sys.go         |  1 +
 src/cmd/gc/walk.c         |  7 ++++++-
 src/runtime/iface.c       | 39 +++++++++++++++++++++++++++++++--------
 4 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/src/cmd/gc/builtin.c.boot b/src/cmd/gc/builtin.c.boot
index 164a27822c..38c8b4cb5e 100644
--- a/src/cmd/gc/builtin.c.boot
+++ b/src/cmd/gc/builtin.c.boot
@@ -32,6 +32,7 @@ char *sysimport =
 	"func sys.ifaceI2T (sigt *uint8, iface any) (ret any)\n"
 	"func sys.ifaceI2T2 (sigt *uint8, iface any) (ret any, ok bool)\n"
 	"func sys.ifaceI2I (sigi *uint8, iface any) (ret any)\n"
+	"func sys.ifaceI2Ix (sigi *uint8, iface any) (ret any)\n"
 	"func sys.ifaceI2I2 (sigi *uint8, iface any) (ret any, ok bool)\n"
 	"func sys.ifaceeq (i1 any, i2 any) (ret bool)\n"
 	"func sys.efaceeq (i1 any, i2 any) (ret bool)\n"
diff --git a/src/cmd/gc/sys.go b/src/cmd/gc/sys.go
index e139e759c6..b5a6ddc2bb 100644
--- a/src/cmd/gc/sys.go
+++ b/src/cmd/gc/sys.go
@@ -42,6 +42,7 @@ func	ifaceT2I(sigi *byte, sigt *byte, elem any) (ret any);
 func	ifaceI2T(sigt *byte, iface any) (ret any);
 func	ifaceI2T2(sigt *byte, iface any) (ret any, ok bool);
 func	ifaceI2I(sigi *byte, iface any) (ret any);
+func	ifaceI2Ix(sigi *byte, iface any) (ret any);
 func	ifaceI2I2(sigi *byte, iface any) (ret any, ok bool);
 func	ifaceeq(i1 any, i2 any) (ret bool);
 func	efaceeq(i1 any, i2 any) (ret bool);
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 18cd2c7eb6..0f160a8a4c 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -12,6 +12,7 @@ enum
 	I2T,
 	I2T2,
 	I2I,
+	I2Ix,
 	I2I2,
 	T2I,
 	I2Isame,
@@ -524,7 +525,7 @@ loop:
 				case I2T:
 					et = I2T2;
 					break;
-				case I2I:
+				case I2Ix:
 					et = I2I2;
 					break;
 				case E2I:
@@ -2947,6 +2948,8 @@ ifaceas1(Type *dst, Type *src, int explicit)
 			ifacecheck(dst, src, lineno, explicit);
 			if(isnilinter(src))
 				return E2I;
+			if(explicit)
+				return I2Ix;
 			return I2I;
 		}
 		if(isnilinter(dst))
@@ -2983,6 +2986,7 @@ ifacename[] =
 	[I2T]		= "ifaceI2T",
 	[I2T2]		= "ifaceI2T2",
 	[I2I]		= "ifaceI2I",
+	[I2Ix]		= "ifaceI2Ix",
 	[I2I2]		= "ifaceI2I2",
 	[I2Isame]	= "ifaceI2Isame",
 	[E2T]		= "ifaceE2T",
@@ -3038,6 +3042,7 @@ ifacecvt(Type *tl, Node *n, int et)
 	case I2T:
 	case I2T2:
 	case I2I:
+	case I2Ix:
 	case I2I2:
 	case E2T:
 	case E2T2:
diff --git a/src/runtime/iface.c b/src/runtime/iface.c
index 9e65a267aa..2351f422d0 100644
--- a/src/runtime/iface.c
+++ b/src/runtime/iface.c
@@ -431,6 +431,7 @@ sys·ifaceI2E(Iface i, Eface ret)
 }
 
 // ifaceI2I(sigi *byte, iface any) (ret any);
+// called only for implicit (no type assertion) conversions
 void
 sys·ifaceI2I(Sigi *si, Iface i, Iface ret)
 {
@@ -438,7 +439,6 @@ sys·ifaceI2I(Sigi *si, Iface i, Iface ret)
 
 	im = i.type;
 	if(im == nil) {
-//TODO(rsc): fixme
 		// If incoming interface is uninitialized (zeroed)
 		// make the outgoing interface zeroed as well.
 		ret = niliface;
@@ -451,6 +451,27 @@ sys·ifaceI2I(Sigi *si, Iface i, Iface ret)
 	FLUSH(&ret);
 }
 
+// ifaceI2Ix(sigi *byte, iface any) (ret any);
+// called only for explicit conversions (with type assertion).
+void
+sys·ifaceI2Ix(Sigi *si, Iface i, Iface ret)
+{
+	Itype *im;
+
+	im = i.type;
+	if(im == nil) {
+		// explicit conversions require non-nil interface value.
+		printf("interface is nil, not %s\n", si->name);
+		throw("interface conversion");
+	} else {
+		ret = i;
+		if(im->sigi != si)
+			ret.type = itype(si, im->sigt, 0);
+	}
+
+	FLUSH(&ret);
+}
+
 // ifaceI2I2(sigi *byte, iface any) (ret any, ok bool);
 void
 sys·ifaceI2I2(Sigi *si, Iface i, Iface ret, bool ok)
@@ -458,14 +479,13 @@ sys·ifaceI2I2(Sigi *si, Iface i, Iface ret, bool ok)
 	Itype *im;
 
 	im = i.type;
-	ok = true;
 	if(im == nil) {
-//TODO: fixme
-		// If incoming interface is uninitialized (zeroed)
-		// make the outgoing interface zeroed as well.
+		// If incoming interface is nil, the conversion fails.
 		ret = niliface;
+		ok = false;
 	} else {
 		ret = i;
+		ok = true;
 		if(im->sigi != si) {
 			ret.type = itype(si, im->sigt, 1);
 			if(ret.type == nil) {
@@ -480,6 +500,7 @@ sys·ifaceI2I2(Sigi *si, Iface i, Iface ret, bool ok)
 }
 
 // ifaceE2I(sigi *byte, iface any) (ret any);
+// Called only for explicit conversions (with type assertion).
 void
 sys·ifaceE2I(Sigi *si, Eface e, Iface ret)
 {
@@ -487,8 +508,9 @@ sys·ifaceE2I(Sigi *si, Eface e, Iface ret)
 
 	t = e.type;
 	if(t == nil) {
-//TODO(rsc): fixme
-		ret = niliface;
+		// explicit conversions require non-nil interface value.
+		printf("interface is nil, not %s\n", si->name);
+		throw("interface conversion");
 	} else {
 		ret.data = e.data;
 		ret.type = itype(si, t, 0);
@@ -505,8 +527,9 @@ sys·ifaceE2I2(Sigi *si, Eface e, Iface ret, bool ok)
 	t = e.type;
 	ok = true;
 	if(t == nil) {
-//TODO(rsc): fixme
+		// If incoming interface is nil, the conversion fails.
 		ret = niliface;
+		ok = false;
 	} else {
 		ret.data = e.data;
 		ret.type = itype(si, t, 1);