runtime: revert init order changes

First, remove the randomization of initialization order.

Then, revert to source code order instead of sorted package path order.

This restores the behavior that was in 1.12.

A larger change which will implement the suggestion in #31636 will
wait for 1.14. It's too complicated for 1.13 at this point (it has
tricky interactions with plugins).

Fixes #31636

Change-Id: I35b48e8cc21cf9f93c0973edd9193d2eac197628
Reviewed-on: https://go-review.googlesource.com/c/go/+/178297
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/init.go

@@ -37,10 +37,8 @@ func fninit(n []*Node) {
 	var fns []*obj.LSym  // functions to call for package initialization
 
 	// Find imported packages with init tasks.
-	for _, p := range types.ImportedPkgList() {
-		if s, ok := p.LookupOK(".inittask"); ok {
-			deps = append(deps, s.Linksym())
-		}
+	for _, s := range types.InitSyms {
+		deps = append(deps, s.Linksym())
 	}
 
 	// Make a function that contains all the initialization statements.

src/cmd/compile/internal/types/pkg.go

@@ -84,6 +84,7 @@ func (pkg *Pkg) Lookup(name string) *Sym {
 	return s
 }
 
+// List of .inittask entries in imported packages, in source code order.
 var InitSyms []*Sym
 
 // LookupOK looks up name in pkg and reports whether it previously existed.
@@ -100,7 +101,7 @@ func (pkg *Pkg) LookupOK(name string) (s *Sym, existed bool) {
 		Name: name,
 		Pkg:  pkg,
 	}
-	if name == "init" {
+	if name == ".inittask" {
 		InitSyms = append(InitSyms, s)
 	}
 	pkg.Syms[name] = s

src/runtime/proc.go

@@ -5211,15 +5211,6 @@ func doInit(t *initTask) {
 		throw("recursive call during initialization - linker skew")
 	default: // not initialized yet
 		t.state = 1 // initialization in progress
-		if raceenabled {
-			// Randomize initialization order of packages t depends on.
-			// TODO: enable always instead of just for race?
-			s := *(*[]uintptr)(unsafe.Pointer(&slice{array: add(unsafe.Pointer(t), 3*sys.PtrSize), len: int(t.ndeps), cap: int(t.ndeps)}))
-			for i := len(s) - 1; i > 0; i-- {
-				j := int(fastrandn(uint32(i + 1)))
-				s[i], s[j] = s[j], s[i]
-			}
-		}
 		for i := uintptr(0); i < t.ndeps; i++ {
 			p := add(unsafe.Pointer(t), (3+i)*sys.PtrSize)
 			t2 := *(**initTask)(p)

test/fixedbugs/issue31636.dir/a.go

@@ -0,0 +1,9 @@
+// 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 a
+
+func init() {
+	println("a")
+}

test/fixedbugs/issue31636.dir/b.go

@@ -0,0 +1,9 @@
+// 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 b
+
+func init() {
+	println("b")
+}

test/fixedbugs/issue31636.dir/c.go

@@ -0,0 +1,9 @@
+// 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 c
+
+func init() {
+	println("c")
+}

test/fixedbugs/issue31636.dir/main.go

@@ -0,0 +1,20 @@
+// 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 main
+
+// We want the initializers of these packages to occur in source code
+// order. See issue 31636. This is the behavior up to and including
+// 1.13. For 1.14, we will move to a variant of lexicographic ordering
+// which will require a change to the test output of this test.
+import (
+	_ "c"
+
+	_ "b"
+
+	_ "a"
+)
+
+func main() {
+}

test/fixedbugs/issue31636.go

@@ -0,0 +1,7 @@
+// rundir
+
+// 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 ignored

test/fixedbugs/issue31636.out

@@ -0,0 +1,3 @@
+c
+b
+a