go/analysis/passes/copylock: suppress error in ill-typed code

The copylock analyzer is marked RunDespiteErrors. In ill-typed
code such as S{T} where S and T are both types, the compiler will
warn that T is not an expression; the copylocks analyzer should
not additionally report a diagnostic as if T had been an expression
of type T.

The fix feels rather ad hoc. In general, analyzers marked
RunDespiteErrors are unlikely to be able to anticipate the
myriad ways that trees can be ill-formed and avoid spurious
diagnostics.

Also, add a main.go file for copylock.

Fixes golang/go#67787

Change-Id: I07afbed16a4138fe602c22ec42171b4a5e634286
Reviewed-on: https://go-review.googlesource.com/c/tools/+/589895
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>

go/analysis/passes/copylock/copylock.go

@@ -240,7 +240,10 @@ func lockPathRhs(pass *analysis.Pass, x ast.Expr) typePath {
 			return nil
 		}
 	}
-	return lockPath(pass.Pkg, pass.TypesInfo.Types[x].Type, nil)
+	if tv, ok := pass.TypesInfo.Types[x]; ok && tv.IsValue() {
+		return lockPath(pass.Pkg, tv.Type, nil)
+	}
+	return nil
 }
 
 // lockPath returns a typePath describing the location of a lock value

go/analysis/passes/copylock/copylock_test.go

@@ -13,5 +13,5 @@ import (
 
 func Test(t *testing.T) {
 	testdata := analysistest.TestData()
-	analysistest.Run(t, testdata, copylock.Analyzer, "a", "typeparams")
+	analysistest.Run(t, testdata, copylock.Analyzer, "a", "typeparams", "issue67787")
 }

go/analysis/passes/copylock/main.go

@@ -0,0 +1,16 @@
+// Copyright 2024 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.
+
+//go:build ignore
+
+// The copylock command applies the golang.org/x/tools/go/analysis/passes/copylock
+// analysis to the specified packages of Go source code.
+package main
+
+import (
+	"golang.org/x/tools/go/analysis/passes/copylock"
+	"golang.org/x/tools/go/analysis/singlechecker"
+)
+
+func main() { singlechecker.Main(copylock.Analyzer) }

go/analysis/passes/copylock/testdata/src/issue67787/issue67787.go

@@ -0,0 +1,8 @@
+package issue67787
+
+import "sync"
+
+type T struct{ mu sync.Mutex }
+type T1 struct{ t *T }
+
+func NewT1() *T1 { return &T1{T} } // no analyzer diagnostic about T