1 files changed, 40 insertions, 0 deletions
diff --git a/test/fixedbugs/issue6977.go b/test/fixedbugs/issue6977.go
new file mode 100644
index 0000000..4525e40
--- /dev/null
+++ b/test/fixedbugs/issue6977.go
@@ -0,0 +1,40 @@
+// errorcheck
+
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+import "io"
+
+// Alan's initial report.
+
+type I interface { f(); String() string }
+type J interface { g(); String() string }
+
+type IJ1 = interface { I; J }
+type IJ2 = interface { f(); g(); String() string }
+
+var _ = (*IJ1)(nil) == (*IJ2)(nil) // static assert that IJ1 and IJ2 are identical types
+
+// The canonical example.
+
+type ReadWriteCloser interface { io.ReadCloser; io.WriteCloser }
+
+// Some more cases.
+
+type M interface { m() }
+type M32 interface { m() int32 }
+type M64 interface { m() int64 }
+
+type U1 interface { m() }
+type U2 interface { m(); M }
+type U3 interface { M; m() }
+type U4 interface { M; M; M }
+type U5 interface { U1; U2; U3; U4 }
+
+type U6 interface { m(); m() } // ERROR "duplicate method .*m"
+type U7 interface { M32; m() } // ERROR "duplicate method .*m"
+type U8 interface { m(); M32 } // ERROR "duplicate method .*m"
+type U9 interface { M32; M64 } // ERROR "duplicate method .*m"