[dev.typeparams] cmd/compile: handle calling a method on a type param in stenciling

 - Have to delay the extra transformation on methods invoked on a type
   param, since the actual transformation (including path through
   embedded fields) will depend on the instantiated type. I am currently
   doing the transformation during the stencil substitution phase. We
   probably should have a separate pass after noder2 and stenciling,
   which drives the extra transformations that were in the old
   typechecker.

 - We handle method values (that are not called) and method calls. We
   don't currently handle method expressions.

 - Handle type substitution in function types, which is needed for
   function args in generic functions.

 - Added stringer.go and map.go tests, testing the above changes
   (including constraints with embedded interfaces).

Change-Id: I3831a937d2b8814150f75bebf9f23ab10b93fa00
Reviewed-on: https://go-review.googlesource.com/c/go/+/290550
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/test/typeparam/map.go b/test/typeparam/map.go
new file mode 100644
index 0000000000..720a52ffbd
--- /dev/null
+++ b/test/typeparam/map.go
@@ -0,0 +1,39 @@
+// 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 main
+
+import (
+	"fmt"
+	"reflect"
+	"strconv"
+)
+
+// Map calls the function f on every element of the slice s,
+// returning a new slice of the results.
+func mapper[F, T any](s []F, f func(F) T) []T {
+	r := make([]T, len(s))
+	for i, v := range s {
+		r[i] = f(v)
+	}
+	return r
+}
+
+func main() {
+	got := mapper([]int{1, 2, 3}, strconv.Itoa)
+	want := []string{"1", "2", "3"}
+	if !reflect.DeepEqual(got, want) {
+		panic(fmt.Sprintf("Got %s, want %s", got, want))
+	}
+
+	fgot := mapper([]float64{2.5, 2.3, 3.5}, func(f float64) string {
+		return strconv.FormatFloat(f, 'f', -1, 64)
+	})
+	fwant := []string{"2.5", "2.3", "3.5"}
+	if !reflect.DeepEqual(fgot, fwant) {
+		panic(fmt.Sprintf("Got %s, want %s", fgot, fwant))
+	}
+}