cmd/compile: import/export of alias declarations

This CL completes support for alias declarations in the compiler.

Also:
- increased export format version
- updated various comments

For #16339.
Fixes #17487.

Change-Id: Ic6945fc44c0041771eaf9dcfe973f601d14de069
Reviewed-on: https://go-review.googlesource.com/32090
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

3 files changed, 181 insertions, 0 deletions

diff --git a/test/alias3.dir/a.go b/test/alias3.dir/a.go
new file mode 100644
index 0000000000..c14f834630
--- /dev/null
+++ b/test/alias3.dir/a.go
@@ -0,0 +1,54 @@
+// Copyright 2016 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
+
+import (
+	"bytes"
+	"go/build"
+	"io"
+	"math"
+)
+
+func F(c *build.Context, w io.Writer) {}
+
+func Inlined() bool { var w Writer; return w == nil }
+
+func Check() {
+	if Pi != math.Pi {
+		panic(0)
+	}
+
+	var w Writer
+	F(new(Context), w)
+	F(new(build.Context), bytes.NewBuffer(nil))
+
+	if &Default != &build.Default {
+		panic(1)
+	}
+
+	if Sin(1) != math.Sin(1) {
+		panic(2)
+	}
+
+	var _ *LimitedReader = new(LimitedReader2)
+}
+
+// export aliases
+const Pi => math.Pi
+
+type (
+	Context => build.Context // not an interface
+	Writer  => io.Writer     // interface
+)
+
+// different aliases may refer to the same original
+type LimitedReader => io.LimitedReader
+type LimitedReader2 => io.LimitedReader
+
+var Default => build.Default
+var Default2 => build.Default
+
+func Sin => math.Sin
+func Sin2 => math.Sin
diff --git a/test/alias3.dir/b.go b/test/alias3.dir/b.go
new file mode 100644
index 0000000000..d4550feca5
--- /dev/null
+++ b/test/alias3.dir/b.go
@@ -0,0 +1,61 @@
+// Copyright 2016 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"
+	"bytes"
+	"go/build"
+	"io"
+	"math"
+)
+
+func F => a.F
+func Inlined => a.Inlined
+
+var _ func(*Context, io.Writer) = a.F
+
+// check aliases
+func Check() {
+	if Pi != math.Pi {
+		panic(0)
+	}
+
+	var w Writer
+	a.F(new(Context), w)
+	F(new(build.Context), bytes.NewBuffer(nil))
+
+	if !Inlined() {
+		panic(1)
+	}
+
+	if &Default != &build.Default {
+		panic(2)
+	}
+
+	if Sin(1) != math.Sin(1) {
+		panic(3)
+	}
+
+	var _ *LimitedReader = new(LimitedReader2)
+}
+
+// re-export aliases
+const Pi => a.Pi
+
+type (
+	Context => a.Context // not an interface
+	Writer  => a.Writer  // interface
+)
+
+// different aliases may refer to the same original
+type LimitedReader => a.LimitedReader
+type LimitedReader2 => a.LimitedReader2
+
+var Default => a.Default
+var Default2 => a.Default2
+
+func Sin => a.Sin
+func Sin2 => a.Sin
diff --git a/test/alias3.dir/c.go b/test/alias3.dir/c.go
new file mode 100644
index 0000000000..701483fac2
--- /dev/null
+++ b/test/alias3.dir/c.go
@@ -0,0 +1,66 @@
+// Copyright 2016 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 main
+
+import (
+	"./a"
+	"./b"
+	"bytes"
+	"go/build"
+	"math"
+)
+
+func f => b.F
+func inlined => b.Inlined
+
+var _ func(*context, a.Writer) = f
+
+func Check() {
+	if pi != math.Pi {
+		panic(0)
+	}
+
+	var w writer
+	b.F(new(context), w)
+	f(new(build.Context), bytes.NewBuffer(nil))
+
+	if !inlined() {
+		panic(1)
+	}
+
+	if &default_ != &build.Default {
+		panic(2)
+	}
+
+	if sin(1) != math.Sin(1) {
+		panic(3)
+	}
+
+	var _ *limitedReader = new(limitedReader2)
+}
+
+// local aliases
+const pi => b.Pi
+
+type (
+	context => b.Context // not an interface
+	writer  => b.Writer  // interface
+)
+
+// different aliases may refer to the same original
+type limitedReader => b.LimitedReader
+type limitedReader2 => b.LimitedReader2
+
+var default_ => b.Default
+var default2 => b.Default2
+
+func sin => b.Sin
+func sin2 => b.Sin
+
+func main() {
+	a.Check()
+	b.Check()
+	Check()
+}