From 6dbaf0352a911f2f4c835dcfbf32aeb38f0b4462 Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Tue, 8 May 2018 18:01:16 -0700
Subject: [PATCH] go/types: better cycle reporting for some cyclic composite
 literals

To evaluate the type of composite literals, the type checker called
Checker.typ which breaks cycles. As a result, certain cycles were
not reported with actual cycle reporting, but caught due to other
uninitialized fields (with less nice error message).

The change now calls Checker.typExpr at the relevant call site.

For #18643.

Change-Id: Iecb3f0e1afb4585b85553b6c581212f52ac3a1c4
Reviewed-on: https://go-review.googlesource.com/115456
Reviewed-by: Alan Donovan <adonovan@google.com>
---
 src/go/types/builtins.go         | 2 +-
 src/go/types/expr.go             | 2 +-
 src/go/types/testdata/cycles.src | 2 +-
 src/go/types/typexpr.go          | 5 +++++
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index afe5f5d0fc..05e032423c 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -174,7 +174,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 			}
 		}
 
-		if mode == invalid {
+		if mode == invalid && typ != Typ[Invalid] {
 			check.invalidArg(x.pos(), "%s for %s", x, bin.name)
 			return
 		}
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 0a2a811bd8..3f3c4f83c6 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -1064,7 +1064,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 					break
 				}
 			}
-			typ = check.typ(e.Type)
+			typ = check.typExpr(e.Type, nil, nil)
 			base = typ
 
 		case hint != nil:
diff --git a/src/go/types/testdata/cycles.src b/src/go/types/testdata/cycles.src
index 79e75e9316..59f112dba1 100644
--- a/src/go/types/testdata/cycles.src
+++ b/src/go/types/testdata/cycles.src
@@ -147,7 +147,7 @@ type (
 // test cases for issue 18643
 // (type cycle detection when non-type expressions are involved)
 type (
-	T14 [len(T14 /* ERROR cycle */ {})]int
+	T14 /* ERROR cycle */ [len(T14{})]int
 	T15 [][len(T15 /* ERROR cycle */ {})]int
 	T16 map[[len(T16 /* ERROR cycle */ {1:2})]int]int
 	T17 map[int][len(T17 /* ERROR cycle */ {1:2})]int
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index e3f50000ec..45ada5874b 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -161,6 +161,11 @@ func (check *Checker) typExpr(e ast.Expr, def *Named, path []*TypeName) (T Type)
 	return
 }
 
+// typ is like typExpr (with a nil argument for the def parameter),
+// but typ breaks type cycles. It should be called for components of
+// types that break cycles, such as pointer base types, slice or map
+// element types, etc. See the comment in typExpr for details.
+//
 func (check *Checker) typ(e ast.Expr) Type {
 	// typExpr is called with a nil path indicating an indirection:
 	// push indir sentinel on object path