go/analysis/passes/tests: update for generics

Warn about Test functions that contain type parameters.

For golang/go#48704

Change-Id: I3f6852613482ec6f33e5650a014564915f11b920
Reviewed-on: https://go-review.googlesource.com/c/tools/+/359494
Run-TryBot: Tim King <taking@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Tim King <taking@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

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

@@ -0,0 +1,10 @@
+// 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
+
+func Zero[T any]() T {
+	var zero T
+	return zero
+}

go/analysis/passes/tests/testdata/src/typeparams/typeparams_test.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 "testing"
+
+func Test(*testing.T) {
+	_ = Zero[int]() // It is fine to use generics within tests.
+}
+
+// Note: We format {Test,Benchmark}typeParam with a 't' in "type" to avoid an error from
+// cmd/go/internal/load. That package can also give an error about Test and Benchmark
+// functions with TypeParameters. These tests may need to be updated if that logic changes.
+func TesttypeParam[T any](*testing.T)      {} // want "TesttypeParam has type parameters: it will not be run by go test as a TestXXX function" "TesttypeParam has malformed name"
+func BenchmarktypeParam[T any](*testing.B) {} // want "BenchmarktypeParam has type parameters: it will not be run by go test as a BenchmarkXXX function" "BenchmarktypeParam has malformed name"
+
+func ExampleZero[T any]() { // want "ExampleZero should not have type params"
+	print(Zero[T]())
+}

go/analysis/passes/tests/tests.go

@@ -16,6 +16,7 @@ import (
 	"unicode/utf8"
 
 	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for common mistaken usages of tests and examples
@@ -170,6 +171,9 @@ func checkExampleName(pass *analysis.Pass, fn *ast.FuncDecl) {
 	if results := fn.Type.Results; results != nil && len(results.List) != 0 {
 		pass.Reportf(fn.Pos(), "%s should return nothing", fnName)
 	}
+	if tparams := typeparams.ForFuncType(fn.Type); tparams != nil && len(tparams.List) > 0 {
+		pass.Reportf(fn.Pos(), "%s should not have type params", fnName)
+	}
 
 	if fnName == "Example" {
 		// Nothing more to do.
@@ -236,6 +240,12 @@ func checkTest(pass *analysis.Pass, fn *ast.FuncDecl, prefix string) {
 		return
 	}
 
+	if tparams := typeparams.ForFuncType(fn.Type); tparams != nil && len(tparams.List) > 0 {
+		// Note: cmd/go/internal/load also errors about TestXXX and BenchmarkXXX functions with type parameters.
+		// We have currently decided to also warn before compilation/package loading. This can help users in IDEs.
+		pass.Reportf(fn.Pos(), "%s has type parameters: it will not be run by go test as a %sXXX function", fn.Name.Name, prefix)
+	}
+
 	if !isTestSuffix(fn.Name.Name[len(prefix):]) {
 		pass.Reportf(fn.Pos(), "%s has malformed name: first letter after '%s' must not be lowercase", fn.Name.Name, prefix)
 	}

go/analysis/passes/tests/tests_test.go

@@ -9,14 +9,18 @@ import (
 
 	"golang.org/x/tools/go/analysis/analysistest"
 	"golang.org/x/tools/go/analysis/passes/tests"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 func Test(t *testing.T) {
 	testdata := analysistest.TestData()
-
-	analysistest.Run(t, testdata, tests.Analyzer,
+	pkgs := []string{
 		"a",        // loads "a", "a [a.test]", and "a.test"
 		"b_x_test", // loads "b" and "b_x_test"
 		"divergent",
-	)
+	}
+	if typeparams.Enabled {
+		pkgs = append(pkgs, "typeparams")
+	}
+	analysistest.Run(t, testdata, tests.Analyzer, pkgs...)
 }