go/analysis/passes/unsafeptr: add tests using generics

Unlike with some other analyzers, it did not seem worthwhile to consider
a type parameter's type set when looking for incorrect conversions to
unsafe.Pointer. There's probably no reason to have a type parameter with
uintptr structural type.

Add some sanity-check tests for the behavior of this analyzer with
respect to generic code.

Updates golang/go#48704

Change-Id: Ibc3180c6eba9c2c88ea2220b1c84cd27971a6700
Reviewed-on: https://go-review.googlesource.com/c/tools/+/360174
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Author: findleyr

go/analysis/passes/unsafeptr/testdata/src/typeparams/typeparams.go

@@ -0,0 +1,21 @@
+// 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 typeparams
+
+import "unsafe"
+
+func _[IntPtr ~uintptr, RealPtr *T, AnyPtr uintptr | *T, T any]() {
+	var (
+		i IntPtr
+		r RealPtr
+		a AnyPtr
+	)
+	_ = unsafe.Pointer(i)          // incorrect, but not detected
+	_ = unsafe.Pointer(i + i)      // incorrect, but not detected
+	_ = unsafe.Pointer(1 + i)      // incorrect, but not detected
+	_ = unsafe.Pointer(uintptr(i)) // want "possible misuse of unsafe.Pointer"
+	_ = unsafe.Pointer(r)
+	_ = unsafe.Pointer(a) // possibly incorrect, but not detected
+}

go/analysis/passes/unsafeptr/unsafeptr_test.go

@@ -9,9 +9,14 @@ import (
 
 	"golang.org/x/tools/go/analysis/analysistest"
 	"golang.org/x/tools/go/analysis/passes/unsafeptr"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 func Test(t *testing.T) {
 	testdata := analysistest.TestData()
-	analysistest.Run(t, testdata, unsafeptr.Analyzer, "a")
+	pkgs := []string{"a"}
+	if typeparams.Enabled {
+		pkgs = append(pkgs, "typeparams")
+	}
+	analysistest.Run(t, testdata, unsafeptr.Analyzer, pkgs...)
 }