// Confirm that when Reader panics, the empty buffer remains empty
	var buf2 Buffer
	defer func() {
		recover()
		check(t, "TestReadFromPanicReader (2)", &buf2, "")
	}()
	buf2.ReadFrom(panicReader{panic: true})
}

func TestReadFromNegativeReader(t *testing.T) {
	var b Buffer
	defer func() {
		switch err := recover().(type) {
		case nil:
			t.Fatal("bytes.Buffer.ReadFrom didn't panic")
		case error:

			t.Fatalf("stdPackages contains unexpected package %s", pkg)
		}
	}
}

func TestIssue64958(t *testing.T) {
	defer func() {
		if x := recover(); x != nil {
			t.Errorf("expected no panic; recovered %v", x)
		}
	}()

	testenv.MustHaveGoBuild(t)

	for _, context := range contexts {
		w := NewWalker(context, "testdata/src/issue64958")

}

func testCallbackPanic(t *testing.T) {
	// Make sure panic during callback unwinds properly.
	if lockedOSThread() {
		t.Fatal("locked OS thread on entry to TestCallbackPanic")
	}
	defer func() {
		s := recover()
		if s == nil {
			t.Fatal("did not panic")
		}
		if s.(string) != "callback panic" {
			t.Fatal("wrong panic:", s)
		}
		if lockedOSThread() {
			t.Fatal("locked OS thread on exit from TestCallbackPanic")

// parse is expected to call any parsing methods that may panic.
// Returns error gathered from recover; nil if no parse errors occurred.
//
// For unexpected panics, calls t.Fatal.
func tryParse(t *testing.T, parse func()) (err error) {
	panicOnError = true
	defer func() {
		panicOnError = false

		e := recover()
		var ok bool
		if err, ok = e.(error); e != nil && !ok {
			t.Fatal(e)
		}
	}()

	parse()

</pre>

<h3 id="Handling_panics">Handling panics</h3>

<p> Two built-in functions, <code>panic</code> and <code>recover</code>,
assist in reporting and handling <a href="#Run_time_panics">run-time panics</a>
and program-defined error conditions.
</p>

<pre class="grammar">
func panic(interface{})
func recover() interface{}
</pre>

<p>
While executing a function <code>F</code>,

		0x4b, 0x05, 0x06, 0x20, 0x20, 0x20, 0x20, 0xff,
		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
		0xff, 0xff, 0xff, 0x20, 0x00,
	}
	defer func() {
		if r := recover(); r != nil {
			t.Fatalf("NewReader panicked: %s", r)
		}
	}()
	// Previously, this would trigger a panic as we attempt to read from
	// an io.SectionReader which would access a slice at a negative offset

	// should panic with a description pointing at the reader, not at itself.
	// (should NOT panic with slice index error, for example.)
	b := NewReader(new(negativeReader))
	defer func() {
		switch err := recover().(type) {
		case nil:
			t.Fatal("read did not panic")
		case error:
			if !strings.Contains(err.Error(), "reader returned negative count from Read") {
				t.Fatalf("wrong panic: %v", err)
			}

// call of panic. If recover is called outside the deferred function it will
// not stop a panicking sequence. In this case, or when the goroutine is not
// panicking, recover returns nil.
//
// Prior to Go 1.21, recover would also return nil if panic is called with
// a nil argument. See [panic] for details.
func recover() any

// The print built-in function formats its arguments in an

</p>

<p>
The return value of <code>recover</code> is <code>nil</code> when the
goroutine is not panicking or <code>recover</code> was not called directly by a deferred function.
Conversely, if a goroutine is panicking and <code>recover</code> was called directly by a deferred function,
the return value of <code>recover</code> is guaranteed not to be <code>nil</code>.

		}
	}
}

// firstError returns the first error value triggered by the input.
func firstError(input *Input) (err error) {
	panicOnError = true
	defer func() {
		panicOnError = false
		switch e := recover(); e := e.(type) {
		case nil:
		case error:
			err = e
		default:
			panic(e)
		}
	}()

	for {
		tok := input.Next()
		if tok == scanner.EOF {
			return
		}
	}