natives/runtime: Update TypeAssertionError instantiation.

dmitshur · dmitshur · commit 1f566bed91de · 2018-08-25T16:05:21.000-04:00
In the relevant upstream change is golang/go@cda1947, fields of TypeAssertionError are changed from string to *_type. This change follows suit and updates the instantiation of the TypeAssertionError type in $assertType of compiler/prelude to use the new definition. This happens when a type assertion fails. Add test coverage for the runtime error string, since it wasn't covered before. Fixes fixedbugs/issue16130.go and fixedbugs/issue26094.go tests.
diff --git a/compiler/natives/src/runtime/runtime.go b/compiler/natives/src/runtime/runtime.go
@@ -17,10 +17,11 @@ type eface struct {
 	_type *_type
 }
 type _type struct {
+	str string
 }
 
 func (t *_type) string() string {
-	return ""
+	return t.str
 }
 func (t *_type) pkgpath() string {
 	return ""
diff --git a/compiler/prelude/types.go b/compiler/prelude/types.go
@@ -729,7 +729,11 @@ var $assertType = function(value, type, returnTuple) {
     if (returnTuple) {
       return [type.zero(), false];
     }
-    $panic(new $packages["runtime"].TypeAssertionError.ptr("", (value === $ifaceNil ? "" : value.constructor.string), type.string, missingMethod));
+    $panic(new $packages["runtime"].TypeAssertionError.ptr(
+      $packages["runtime"]._type.ptr.nil,
+      (value === $ifaceNil ? $packages["runtime"]._type.ptr.nil : new $packages["runtime"]._type.ptr(value.constructor.string)),
+      new $packages["runtime"]._type.ptr(type.string),
+      missingMethod));
   }
 
   if (!isInterface) {
diff --git a/tests/misc_test.go b/tests/misc_test.go
@@ -672,3 +672,26 @@ func TestSlicingNilSlice(t *testing.T) {
 		}
 	})
 }
+
+// Ensure that doing an interface conversion that fails
+// produces an expected error type with the right error text.
+func TestInterfaceConversionRuntimeError(t *testing.T) {
+	defer func() {
+		r := recover()
+		if r == nil {
+			t.Fatal("got no panic, want panic")
+		}
+		re, ok := r.(runtime.Error)
+		if !ok {
+			t.Fatalf("got %T, want runtime.Error", r)
+		}
+		if got, want := re.Error(), "interface conversion: int is not tests.I: missing method Get"; got != want {
+			t.Fatalf("got %q, want %q", got, want)
+		}
+	}()
+	type I interface {
+		Get() int
+	}
+	e := (interface{})(0)
+	_ = e.(I)
+}

Original file line number	Diff line number	Diff line change
`@@ -17,10 +17,11 @@ type eface struct {`
`17`	`17`	`_type *_type`
`18`	`18`	`}`
`19`	`19`	`type _type struct {`
	`20`	`+ str string`
`20`	`21`	`}`
`21`	`22`
`22`	`23`	`func (t *_type) string() string {`
`23`		`- return ""`
	`24`	`+ return t.str`
`24`	`25`	`}`
`25`	`26`	`func (t *_type) pkgpath() string {`
`26`	`27`	`return ""`
Original file line number	Diff line number	Diff line change
`@@ -729,7 +729,11 @@ var $assertType = function(value, type, returnTuple) {`
`729`	`729`	`if (returnTuple) {`
`730`	`730`	`return [type.zero(), false];`
`731`	`731`	`}`
`732`		`- $panic(new $packages["runtime"].TypeAssertionError.ptr("", (value === $ifaceNil ? "" : value.constructor.string), type.string, missingMethod));`
	`732`	`+ $panic(new $packages["runtime"].TypeAssertionError.ptr(`
	`733`	`+ $packages["runtime"]._type.ptr.nil,`
	`734`	`+ (value === $ifaceNil ? $packages["runtime"]._type.ptr.nil : new $packages["runtime"]._type.ptr(value.constructor.string)),`
	`735`	`+ new $packages["runtime"]._type.ptr(type.string),`
	`736`	`+ missingMethod));`
`733`	`737`	`}`
`734`	`738`
`735`	`739`	`if (!isInterface) {`