[dev.typeparams] cmd/compile/internal/types2: delay interface check for type bounds

While at it, clean up code for collecting/declaring type parameters.

For #40789.

Change-Id: I0855137d5ee85c0ae2fa60d33b28c24a33132fbc
Reviewed-on: https://go-review.googlesource.com/c/go/+/331690
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/testdata/fixedbugs/issue40789.go2 b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue40789.go2
new file mode 100644
index 0000000000..9eea4ad60a
--- /dev/null
+++ b/src/cmd/compile/internal/types2/testdata/fixedbugs/issue40789.go2
@@ -0,0 +1,37 @@
+// 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 main
+
+import "fmt"
+
+func main() {
+	m := map[string]int{
+		"a": 6,
+		"b": 7,
+	}
+	fmt.Println(copyMap[map[string]int, string, int](m))
+}
+
+type Map[K comparable, V any] interface {
+	map[K] V
+}
+
+func copyMap[M Map[K, V], K comparable, V any](m M) M {
+	m1 := make(M)
+	for k, v := range m {
+		m1[k] = v
+	}
+	return m1
+}
+
+// simpler test case from the same issue
+
+type A[X comparable] interface {
+	[]X
+}
+
+func f[B A[X], X comparable]() B {
+	return nil
+}