cmd/compile: fix generic type handling when crawling inline body

For base generic type that is written to export file, we need to mark
all of its methods, include exported+unexported methods, as reachable,
so they can be available for instantiation if necessary. But markType
only looks for exported methods, thus causing the crash in #49143.

To fix this, we introduce new method p.markGeneric, to mark all methods
of the base generic type.

This issue has happend for a while (maybe since we add generic
import/export during go1.18 cycle), and was un-intentionally "fixed" in
CL 356254, when we agresssively call p.markEmbed(t). CL 357232 fixed
that wrong agressive behavior, thus reproduce the bug on tip.

Fixes #49143

Change-Id: Ie64574a05fffb282e9dcc8739df4378c5b6b0468
Reviewed-on: https://go-review.googlesource.com/c/go/+/358814
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

src/cmd/compile/internal/typecheck/crawler.go

@@ -20,6 +20,7 @@ func crawlExports(exports []*ir.Name) {
 	p := crawler{
 		marked:   make(map[*types.Type]bool),
 		embedded: make(map[*types.Type]bool),
+		generic:  make(map[*types.Type]bool),
 	}
 	for _, n := range exports {
 		p.markObject(n)
@@ -29,6 +30,7 @@ func crawlExports(exports []*ir.Name) {
 type crawler struct {
 	marked   map[*types.Type]bool // types already seen by markType
 	embedded map[*types.Type]bool // types already seen by markEmbed
+	generic  map[*types.Type]bool // types already seen by markGeneric
 }
 
 // markObject visits a reachable object (function, method, global type, or global variable)
@@ -168,6 +170,30 @@ func (p *crawler) markEmbed(t *types.Type) {
 	}
 }
 
+// markGeneric takes an instantiated type or a base generic type t, and
+// marks all the methods of the base generic type of t. If a base generic
+// type is written to export file, even if not explicitly marked for export,
+// all of its methods need to be available for instantiation if needed.
+func (p *crawler) markGeneric(t *types.Type) {
+	if t.IsPtr() {
+		t = t.Elem()
+	}
+	if t.OrigSym() != nil {
+		// Convert to the base generic type.
+		t = t.OrigSym().Def.Type()
+	}
+	if p.generic[t] {
+		return
+	}
+	p.generic[t] = true
+
+	if t.Sym() != nil && t.Kind() != types.TINTER {
+		for _, m := range t.Methods().Slice() {
+			p.markObject(m.Nname.(*ir.Name))
+		}
+	}
+}
+
 // markInlBody marks n's inline body for export and recursively
 // ensures all called functions are marked too.
 func (p *crawler) markInlBody(n *ir.Name) {
@@ -197,12 +223,7 @@ func (p *crawler) markInlBody(n *ir.Name) {
 		t := n.Type()
 		if t != nil {
 			if t.HasTParam() || t.IsFullyInstantiated() {
-				// Ensure that we call markType() on any base generic type
+				p.markGeneric(t)
-				// that is written to the export file (even if not explicitly
-				// marked for export), so we will call markInlBody on its
-				// methods, and the methods will be available for
-				// instantiation if needed.
-				p.markType(t)
 			}
 			if base.Debug.Unified == 0 {
 				// If a method of un-exported type is promoted and accessible by

test/fixedbugs/issue49143.dir/a.go

@@ -0,0 +1,24 @@
+// Copyright 2021 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 "sync"
+
+type Loader[K comparable, R any] struct {
+	batch *LoaderBatch[K, R]
+}
+
+func (l *Loader[K, R]) Load() error {
+	l.batch.f()
+	return nil
+}
+
+type LoaderBatch[K comparable, R any] struct {
+	once    *sync.Once
+}
+
+func (b *LoaderBatch[K, R]) f() {
+	b.once.Do(func() {})
+}

test/fixedbugs/issue49143.dir/b.go

@@ -0,0 +1,16 @@
+// Copyright 2021 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"
+
+
+type Loaders struct {
+	Loader *a.Loader[int, int]
+}
+
+func NewLoaders() *Loaders {
+	return new(Loaders)
+}

test/fixedbugs/issue49143.dir/c.go

@@ -0,0 +1,15 @@
+// Copyright 2021 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
+
+import "./b"
+
+type Resolver struct{}
+
+type todoResolver struct{ *Resolver }
+
+func (r *todoResolver) F() {
+	b.NewLoaders().Loader.Load()
+}

test/fixedbugs/issue49143.dir/p.go

@@ -0,0 +1,11 @@
+// Copyright 2021 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 (
+	"./c"
+)
+
+var _ = &c.Resolver{}

test/fixedbugs/issue49143.go

@@ -0,0 +1,7 @@
+// compiledir -G=3
+
+// Copyright 2021 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