cmd/compile: fix various small bugs related to type lists

Fix various small bugs related to delaying transformations due to type
params. Most of these relate to the need to delay a transformation when
an argument of an expression or statement has a type parameter that has
a structural constraint. The structural constraint implies the operation
should work, but the transformation can't happen until the actual value
of the type parameter is known.

 - delay transformations for send statements and return statements if
   any args/values have type params.

 - similarly, delay transformation of a call where the function arg has
   type parameters. This is mainly important for the case where the
   function arg is a pure type parameter, but has a structural
   constraint that requires it to be a function. Move the setting of
   n.Use to transformCall(), since we may not know how many return
   values there are until then, if the function arg is a type parameter.

 - set the type of unary expressions from the type2 type (as we do with
   most other expressions), since that works better with expressions
   with type params.

 - deal with these delayed transformations in subster.node() and convert
   the CALL checks to a switch statement.

 - make sure ir.CurFunc is set properly during stenciling, including
   closures (needed for transforming return statements during
   stenciling).

New test file typelist.go with tests for these cases.

Change-Id: I1b82f949d8cec47d906429209e846f4ebc8ec85e
Reviewed-on: https://go-review.googlesource.com/c/go/+/305729
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/test/typeparam/typelist.go b/test/typeparam/typelist.go
new file mode 100644
index 0000000000..4ff3ce2f34
--- /dev/null
+++ b/test/typeparam/typelist.go
@@ -0,0 +1,64 @@
+// compile -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.
+
+// This file tests type lists & structural constraints.
+
+package p
+
+// Assignability of an unnamed pointer type to a type parameter that
+// has a matching underlying type.
+func _[T interface{}, PT interface{type *T}] (x T) PT {
+    return &x
+}
+
+// Indexing of generic types containing type parameters in their type list:
+func at[T interface{ type []E }, E any](x T, i int) E {
+        return x[i]
+}
+
+// A generic type inside a function acts like a named type. Its underlying
+// type is itself, its "operational type" is defined by the type list in
+// the tybe bound, if any.
+func _[T interface{type int}](x T) {
+	type myint int
+	var _ int = int(x)
+	var _ T = 42
+	var _ T = T(myint(42))
+}
+
+// Indexing a generic type which has a structural contraints to be an array.
+func _[T interface { type [10]int }](x T) {
+	_ = x[9] // ok
+}
+
+// Dereference of a generic type which has a structural contraint to be a pointer.
+func _[T interface{ type *int }](p T) int {
+	return *p
+}
+
+// Channel send and receive on a generic type which has a structural constraint to
+// be a channel.
+func _[T interface{ type chan int }](ch T) int {
+	// This would deadlock if executed (but ok for a compile test)
+	ch <- 0
+	return <- ch
+}
+
+// Calling of a generic type which has a structural constraint to be a function.
+func _[T interface{ type func() }](f T) {
+	f()
+	go f()
+}
+
+// Same, but function has a parameter and return value.
+func _[T interface{ type func(string) int }](f T) int {
+	return f("hello")
+}
+
+// Map access of a generic type which has a structural constraint to be a map.
+func _[V any, T interface { type map[string]V }](p T) V {
+	return p["test"]
+}