cmd/compile: add support for generic channels and type conversion during calls

Add support for channels in subster.typ(). Add new test file chans.go.

To support assignability of bidirectional channel args to directional
channel params, I needed to type check generic calls after they are
instantiated. (Eventually, we will create separate functions to just do
the assignability logic, so we don't need to call the old typechecker in
this case.) So, for generic calls, we now leave the call as OCALL (as a
signal that the call still needs typechecking), and do typecheck.Call()
during stenciling.

Smaller changes:
 - Set the type of an instantiated OCLOSURE node (and not just the associated
   OFUNC node)

 - In instTypeName2, filter out the space that types2.TypeString inserts
   after a common in a typelist. Our standard naming requires no space
   after the comma.

 - With the assignability fix above, I no longer need the explicit
   conversions in cons.go.

Change-Id: I148858bfc6708c0aa3f50bad7debce2b8c8c091f
Reviewed-on: https://go-review.googlesource.com/c/go/+/301669
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 413 insertions, 0 deletions

diff --git a/test/typeparam/chans.go b/test/typeparam/chans.go
new file mode 100644
index 0000000000..2fcd4af75e
--- /dev/null
+++ b/test/typeparam/chans.go
@@ -0,0 +1,413 @@
+// run -gcflags=-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 chans provides utility functions for working with channels.
+package main
+
+import (
+	"context"
+	"fmt"
+	"runtime"
+	"sort"
+	"sync"
+	"time"
+)
+
+// _Equal reports whether two slices are equal: the same length and all
+// elements equal. All floating point NaNs are considered equal.
+func _SliceEqual[Elem comparable](s1, s2 []Elem) bool {
+	if len(s1) != len(s2) {
+		return false
+	}
+	for i, v1 := range s1 {
+		v2 := s2[i]
+		if v1 != v2 {
+			isNaN := func(f Elem) bool { return f != f }
+			if !isNaN(v1) || !isNaN(v2) {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// _ReadAll reads from c until the channel is closed or the context is
+// canceled, returning all the values read.
+func _ReadAll[Elem any](ctx context.Context, c <-chan Elem) []Elem {
+	var r []Elem
+	for {
+		select {
+		case <-ctx.Done():
+			return r
+		case v, ok := <-c:
+			if !ok {
+				return r
+			}
+			r = append(r, v)
+		}
+	}
+}
+
+// _Merge merges two channels into a single channel.
+// This will leave a goroutine running until either both channels are closed
+// or the context is canceled, at which point the returned channel is closed.
+func _Merge[Elem any](ctx context.Context, c1, c2 <-chan Elem) <-chan Elem {
+	r := make(chan Elem)
+	go func(ctx context.Context, c1, c2 <-chan Elem, r chan<- Elem) {
+		defer close(r)
+		for c1 != nil || c2 != nil {
+			select {
+			case <-ctx.Done():
+				return
+			case v1, ok := <-c1:
+				if ok {
+					r <- v1
+				} else {
+					c1 = nil
+				}
+			case v2, ok := <-c2:
+				if ok {
+					r <- v2
+				} else {
+					c2 = nil
+				}
+			}
+		}
+	}(ctx, c1, c2, r)
+	return r
+}
+
+// _Filter calls f on each value read from c. If f returns true the value
+// is sent on the returned channel. This will leave a goroutine running
+// until c is closed or the context is canceled, at which point the
+// returned channel is closed.
+func _Filter[Elem any](ctx context.Context, c <-chan Elem, f func(Elem) bool) <-chan Elem {
+	r := make(chan Elem)
+	go func(ctx context.Context, c <-chan Elem, f func(Elem) bool, r chan<- Elem) {
+		defer close(r)
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case v, ok := <-c:
+				if !ok {
+					return
+				}
+				if f(v) {
+					r <- v
+				}
+			}
+		}
+	}(ctx, c, f, r)
+	return r
+}
+
+// _Sink returns a channel that discards all values sent to it.
+// This will leave a goroutine running until the context is canceled
+// or the returned channel is closed.
+func _Sink[Elem any](ctx context.Context) chan<- Elem {
+	r := make(chan Elem)
+	go func(ctx context.Context, r <-chan Elem) {
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case _, ok := <-r:
+				if !ok {
+					return
+				}
+			}
+		}
+	}(ctx, r)
+	return r
+}
+
+// An Exclusive is a value that may only be used by a single goroutine
+// at a time. This is implemented using channels rather than a mutex.
+type _Exclusive[Val any] struct {
+	c chan Val
+}
+
+// _MakeExclusive makes an initialized exclusive value.
+func _MakeExclusive[Val any](initial Val) *_Exclusive[Val] {
+	r := &_Exclusive[Val]{
+		c: make(chan Val, 1),
+	}
+	r.c <- initial
+	return r
+}
+
+// _Acquire acquires the exclusive value for private use.
+// It must be released using the Release method.
+func (e *_Exclusive[Val]) Acquire() Val {
+	return <-e.c
+}
+
+// TryAcquire attempts to acquire the value. The ok result reports whether
+// the value was acquired. If the value is acquired, it must be released
+// using the Release method.
+func (e *_Exclusive[Val]) TryAcquire() (v Val, ok bool) {
+	select {
+	case r := <-e.c:
+		return r, true
+	default:
+		return v, false
+	}
+}
+
+// Release updates and releases the value.
+// This method panics if the value has not been acquired.
+func (e *_Exclusive[Val]) Release(v Val) {
+	select {
+	case e.c <- v:
+	default:
+		panic("_Exclusive Release without Acquire")
+	}
+}
+
+// Ranger returns a Sender and a Receiver. The Receiver provides a
+// Next method to retrieve values. The Sender provides a Send method
+// to send values and a Close method to stop sending values. The Next
+// method indicates when the Sender has been closed, and the Send
+// method indicates when the Receiver has been freed.
+//
+// This is a convenient way to exit a goroutine sending values when
+// the receiver stops reading them.
+func _Ranger[Elem any]() (*_Sender[Elem], *_Receiver[Elem]) {
+	c := make(chan Elem)
+	d := make(chan struct{})
+	s := &_Sender[Elem]{
+		values: c,
+		done:   d,
+	}
+	r := &_Receiver[Elem] {
+		values: c,
+		done:   d,
+	}
+	runtime.SetFinalizer(r, (*_Receiver[Elem]).finalize)
+	return s, r
+}
+
+// A _Sender is used to send values to a Receiver.
+type _Sender[Elem any] struct {
+	values chan<- Elem
+	done   <-chan struct{}
+}
+
+// Send sends a value to the receiver. It reports whether the value was sent.
+// The value will not be sent if the context is closed or the receiver
+// is freed.
+func (s *_Sender[Elem]) Send(ctx context.Context, v Elem) bool {
+	select {
+	case <-ctx.Done():
+		return false
+	case s.values <- v:
+		return true
+	case <-s.done:
+		return false
+	}
+}
+
+// Close tells the receiver that no more values will arrive.
+// After Close is called, the _Sender may no longer be used.
+func (s *_Sender[Elem]) Close() {
+	close(s.values)
+}
+
+// A _Receiver receives values from a _Sender.
+type _Receiver[Elem any] struct {
+	values <-chan Elem
+	done   chan<- struct{}
+}
+
+// Next returns the next value from the channel. The bool result indicates
+// whether the value is valid.
+func (r *_Receiver[Elem]) Next(ctx context.Context) (v Elem, ok bool) {
+	select {
+	case <-ctx.Done():
+	case v, ok = <-r.values:
+	}
+	return v, ok
+}
+
+// finalize is a finalizer for the receiver.
+func (r *_Receiver[Elem]) finalize() {
+	close(r.done)
+}
+
+func TestReadAll() {
+	c := make(chan int)
+	go func() {
+		c <- 4
+		c <- 2
+		c <- 5
+		close(c)
+	}()
+	got := _ReadAll(context.Background(), c)
+	want := []int{4, 2, 5}
+	if !_SliceEqual(got, want) {
+		panic(fmt.Sprintf("_ReadAll returned %v, want %v", got, want))
+	}
+}
+
+func TestMerge() {
+	c1 := make(chan int)
+	c2 := make(chan int)
+	go func() {
+		c1 <- 1
+		c1 <- 3
+		c1 <- 5
+		close(c1)
+	}()
+	go func() {
+		c2 <- 2
+		c2 <- 4
+		c2 <- 6
+		close(c2)
+	}()
+	ctx := context.Background()
+	got := _ReadAll(ctx, _Merge(ctx, c1, c2))
+	sort.Ints(got)
+	want := []int{1, 2, 3, 4, 5, 6}
+	if !_SliceEqual(got, want) {
+		panic(fmt.Sprintf("_Merge returned %v, want %v", got, want))
+	}
+}
+
+func TestFilter() {
+	c := make(chan int)
+	go func() {
+		c <- 1
+		c <- 2
+		c <- 3
+		close(c)
+	}()
+	even := func(i int) bool { return i%2 == 0 }
+	ctx := context.Background()
+	got := _ReadAll(ctx, _Filter(ctx, c, even))
+	want := []int{2}
+	if !_SliceEqual(got, want) {
+		panic(fmt.Sprintf("_Filter returned %v, want %v", got, want))
+	}
+}
+
+func TestSink() {
+	c := _Sink[int](context.Background())
+	after := time.NewTimer(time.Minute)
+	defer after.Stop()
+	send := func(v int) {
+		select {
+		case c <- v:
+		case <-after.C:
+			panic("timed out sending to _Sink")
+		}
+	}
+	send(1)
+	send(2)
+	send(3)
+	close(c)
+}
+
+func TestExclusive() {
+	val := 0
+	ex := _MakeExclusive(&val)
+
+	var wg sync.WaitGroup
+	f := func() {
+		defer wg.Done()
+		for i := 0; i < 10; i++ {
+			p := ex.Acquire()
+			(*p)++
+			ex.Release(p)
+		}
+	}
+
+	wg.Add(2)
+	go f()
+	go f()
+
+	wg.Wait()
+	if val != 20 {
+		panic(fmt.Sprintf("after Acquire/Release loop got %d, want 20", val))
+	}
+}
+
+func TestExclusiveTry() {
+	s := ""
+	ex := _MakeExclusive(&s)
+	p, ok := ex.TryAcquire()
+	if !ok {
+		panic("TryAcquire failed")
+	}
+	*p = "a"
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		_, ok := ex.TryAcquire()
+		if ok {
+			panic(fmt.Sprintf("TryAcquire succeeded unexpectedly"))
+		}
+	}()
+	wg.Wait()
+
+	ex.Release(p)
+
+	p, ok = ex.TryAcquire()
+	if !ok {
+		panic(fmt.Sprintf("TryAcquire failed"))
+	}
+}
+
+func TestRanger() {
+	s, r := _Ranger[int]()
+
+	ctx := context.Background()
+	go func() {
+		// Receive one value then exit.
+		v, ok := r.Next(ctx)
+		if !ok {
+			panic(fmt.Sprintf("did not receive any values"))
+		} else if v != 1 {
+			panic(fmt.Sprintf("received %d, want 1", v))
+		}
+	}()
+
+	c1 := make(chan bool)
+	c2 := make(chan bool)
+	go func() {
+		defer close(c2)
+		if !s.Send(ctx, 1) {
+			panic(fmt.Sprintf("Send failed unexpectedly"))
+		}
+		close(c1)
+		if s.Send(ctx, 2) {
+			panic(fmt.Sprintf("Send succeeded unexpectedly"))
+		}
+	}()
+
+	<-c1
+
+	// Force a garbage collection to try to get the finalizers to run.
+	runtime.GC()
+
+	select {
+	case <-c2:
+	case <-time.After(time.Minute):
+		panic("_Ranger Send should have failed, but timed out")
+	}
+}
+
+func main() {
+	TestReadAll()
+	TestMerge()
+	TestFilter()
+	TestSink()
+	TestExclusive()
+	TestExclusiveTry()
+	TestRanger()
+}