From 8d5fd871d79bd62b04bfadb3b7be0a896029e80c Mon Sep 17 00:00:00 2001
From: Matthew Dempsky <mdempsky@google.com>
Date: Fri, 6 Jul 2018 12:14:22 -0700
Subject: [PATCH] cmd/compile: fix "width not calculated" ICE

Expanding interface method sets is handled during width calculation,
which can't be performed concurrently. Make sure that we eagerly
expand interfaces in the frontend when importing them, even if they're
not actually used by code, because we might need to generate a type
description of them.

Fixes #25055.

Change-Id: I6fd2756de2c7d5dbc33056f70b3028ca3aebab41
Reviewed-on: https://go-review.googlesource.com/122517
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
---
 src/cmd/compile/internal/gc/iimport.go | 19 +++++++++++++++++++
 test/fixedbugs/issue25055.dir/a.go     |  7 +++++++
 test/fixedbugs/issue25055.dir/b.go     |  9 +++++++++
 test/fixedbugs/issue25055.go           |  7 +++++++
 4 files changed, 42 insertions(+)
 create mode 100644 test/fixedbugs/issue25055.dir/a.go
 create mode 100644 test/fixedbugs/issue25055.dir/b.go
 create mode 100644 test/fixedbugs/issue25055.go

diff --git a/src/cmd/compile/internal/gc/iimport.go b/src/cmd/compile/internal/gc/iimport.go
index 54c5d8dc2f..21151b5215 100644
--- a/src/cmd/compile/internal/gc/iimport.go
+++ b/src/cmd/compile/internal/gc/iimport.go
@@ -296,8 +296,23 @@ func (r *importReader) doDecl(n *Node) {
 		// declaration before recursing.
 		t := importtype(r.p.ipkg, pos, n.Sym)
 
+		// We also need to defer width calculations until
+		// after the underlying type has been assigned.
+		//
+		// TODO(mdempsky): Add nesting support directly to
+		// {defer,resume}checkwidth? Width calculations are
+		// already deferred during initial typechecking, but
+		// not when we're expanding inline function bodies, so
+		// we currently need to handle both cases here.
+		deferring := defercalc != 0
+		if !deferring {
+			defercheckwidth()
+		}
 		underlying := r.typ()
 		copytype(typenod(t), underlying)
+		if !deferring {
+			resumecheckwidth()
+		}
 
 		if underlying.IsInterface() {
 			break
@@ -576,6 +591,10 @@ func (r *importReader) typ1() *types.Type {
 		t := types.New(TINTER)
 		t.SetPkg(r.currPkg)
 		t.SetInterface(append(embeddeds, methods...))
+
+		// Ensure we expand the interface in the frontend (#25055).
+		checkwidth(t)
+
 		return t
 	}
 }
diff --git a/test/fixedbugs/issue25055.dir/a.go b/test/fixedbugs/issue25055.dir/a.go
new file mode 100644
index 0000000000..7fea195e2b
--- /dev/null
+++ b/test/fixedbugs/issue25055.dir/a.go
@@ -0,0 +1,7 @@
+// Copyright 2018 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 a
+
+var A chan *interface{}
diff --git a/test/fixedbugs/issue25055.dir/b.go b/test/fixedbugs/issue25055.dir/b.go
new file mode 100644
index 0000000000..01efeae3e6
--- /dev/null
+++ b/test/fixedbugs/issue25055.dir/b.go
@@ -0,0 +1,9 @@
+// Copyright 2018 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 b
+
+import "./a"
+
+var _ = <-a.A
diff --git a/test/fixedbugs/issue25055.go b/test/fixedbugs/issue25055.go
new file mode 100644
index 0000000000..0e15a8e71f
--- /dev/null
+++ b/test/fixedbugs/issue25055.go
@@ -0,0 +1,7 @@
+// compiledir -c=2
+
+// Copyright 2018 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 ignored