Adding upstream version 1.22.1.upstream/1.22.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1297 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/rangefunc/rangefunc_test.go b/src/cmd/compile/internal/rangefunc/rangefunc_test.go
new file mode 100644
index 0000000..16856c6
--- /dev/null
+++ b/src/cmd/compile/internal/rangefunc/rangefunc_test.go
@@ -0,0 +1,1297 @@
+// Copyright 2023 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 goexperiment.rangefunc
+
+package rangefunc_test
+
+import (
+	"slices"
+	"testing"
+)
+
+type Seq2[T1, T2 any] func(yield func(T1, T2) bool)
+
+// OfSliceIndex returns a Seq over the elements of s. It is equivalent
+// to range s.
+func OfSliceIndex[T any, S ~[]T](s S) Seq2[int, T] {
+	return func(yield func(int, T) bool) {
+		for i, v := range s {
+			if !yield(i, v) {
+				return
+			}
+		}
+		return
+	}
+}
+
+// BadOfSliceIndex is "bad" because it ignores the return value from yield
+// and just keeps on iterating.
+func BadOfSliceIndex[T any, S ~[]T](s S) Seq2[int, T] {
+	return func(yield func(int, T) bool) {
+		for i, v := range s {
+			yield(i, v)
+		}
+		return
+	}
+}
+
+// VeryBadOfSliceIndex is "very bad" because it ignores the return value from yield
+// and just keeps on iterating, and also wraps that call in a defer-recover so it can
+// keep on trying after the first panic.
+func VeryBadOfSliceIndex[T any, S ~[]T](s S) Seq2[int, T] {
+	return func(yield func(int, T) bool) {
+		for i, v := range s {
+			func() {
+				defer func() {
+					recover()
+				}()
+				yield(i, v)
+			}()
+		}
+		return
+	}
+}
+
+// CooperativeBadOfSliceIndex calls the loop body from a goroutine after
+// a ping on a channel, and returns recover()on that same channel.
+func CooperativeBadOfSliceIndex[T any, S ~[]T](s S, proceed chan any) Seq2[int, T] {
+	return func(yield func(int, T) bool) {
+		for i, v := range s {
+			if !yield(i, v) {
+				// if the body breaks, call yield just once in a goroutine
+				go func() {
+					<-proceed
+					defer func() {
+						proceed <- recover()
+					}()
+					yield(0, s[0])
+				}()
+				return
+			}
+		}
+		return
+	}
+}
+
+// TrickyIterator is a type intended to test whether an iterator that
+// calls a yield function after loop exit must inevitably escape the
+// closure; this might be relevant to future checking/optimization.
+type TrickyIterator struct {
+	yield func(int, int) bool
+}
+
+func (ti *TrickyIterator) iterAll(s []int) Seq2[int, int] {
+	return func(yield func(int, int) bool) {
+		ti.yield = yield // Save yield for future abuse
+		for i, v := range s {
+			if !yield(i, v) {
+				return
+			}
+		}
+		return
+	}
+}
+
+func (ti *TrickyIterator) iterOne(s []int) Seq2[int, int] {
+	return func(yield func(int, int) bool) {
+		ti.yield = yield // Save yield for future abuse
+		if len(s) > 0 {  // Not in a loop might escape differently
+			yield(0, s[0])
+		}
+		return
+	}
+}
+
+func (ti *TrickyIterator) iterZero(s []int) Seq2[int, int] {
+	return func(yield func(int, int) bool) {
+		ti.yield = yield // Save yield for future abuse
+		// Don't call it at all, maybe it won't escape
+		return
+	}
+}
+
+func (ti *TrickyIterator) fail() {
+	if ti.yield != nil {
+		ti.yield(1, 1)
+	}
+}
+
+// Check wraps the function body passed to iterator forall
+// in code that ensures that it cannot (successfully) be called
+// either after body return false (control flow out of loop) or
+// forall itself returns (the iteration is now done).
+//
+// Note that this can catch errors before the inserted checks.
+func Check[U, V any](forall Seq2[U, V]) Seq2[U, V] {
+	return func(body func(U, V) bool) {
+		ret := true
+		forall(func(u U, v V) bool {
+			if !ret {
+				panic("Checked iterator access after exit")
+			}
+			ret = body(u, v)
+			return ret
+		})
+		ret = false
+	}
+}
+
+func TestCheck(t *testing.T) {
+	i := 0
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+	for _, x := range Check(BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})) {
+		i += x
+		if i > 4*9 {
+			break
+		}
+	}
+}
+
+func TestCooperativeBadOfSliceIndex(t *testing.T) {
+	i := 0
+	proceed := make(chan any)
+	for _, x := range CooperativeBadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, proceed) {
+		i += x
+		if i >= 36 {
+			break
+		}
+	}
+	proceed <- true
+	if r := <-proceed; r != nil {
+		t.Logf("Saw expected panic '%v'", r)
+	} else {
+		t.Error("Wanted to see a failure")
+	}
+	if i != 36 {
+		t.Errorf("Expected i == 36, saw %d instead", i)
+	} else {
+		t.Logf("i = %d", i)
+	}
+}
+
+func TestCheckCooperativeBadOfSliceIndex(t *testing.T) {
+	i := 0
+	proceed := make(chan any)
+	for _, x := range Check(CooperativeBadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, proceed)) {
+		i += x
+		if i >= 36 {
+			break
+		}
+	}
+	proceed <- true
+	if r := <-proceed; r != nil {
+		t.Logf("Saw expected panic '%v'", r)
+	} else {
+		t.Error("Wanted to see a failure")
+	}
+	if i != 36 {
+		t.Errorf("Expected i == 36, saw %d instead", i)
+	} else {
+		t.Logf("i = %d", i)
+	}
+}
+
+func TestTrickyIterAll(t *testing.T) {
+	trickItAll := TrickyIterator{}
+	i := 0
+	for _, x := range trickItAll.iterAll([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+		i += x
+		if i >= 36 {
+			break
+		}
+	}
+
+	if i != 36 {
+		t.Errorf("Expected i == 36, saw %d instead", i)
+	} else {
+		t.Logf("i = %d", i)
+	}
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	trickItAll.fail()
+}
+
+func TestTrickyIterOne(t *testing.T) {
+	trickItOne := TrickyIterator{}
+	i := 0
+	for _, x := range trickItOne.iterOne([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+		i += x
+		if i >= 36 {
+			break
+		}
+	}
+
+	// Don't care about value, ought to be 36 anyhow.
+	t.Logf("i = %d", i)
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	trickItOne.fail()
+}
+
+func TestTrickyIterZero(t *testing.T) {
+	trickItZero := TrickyIterator{}
+	i := 0
+	for _, x := range trickItZero.iterZero([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+		i += x
+		if i >= 36 {
+			break
+		}
+	}
+
+	// Don't care about value, ought to be 0 anyhow.
+	t.Logf("i = %d", i)
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	trickItZero.fail()
+}
+
+func TestCheckTrickyIterZero(t *testing.T) {
+	trickItZero := TrickyIterator{}
+	i := 0
+	for _, x := range Check(trickItZero.iterZero([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})) {
+		i += x
+		if i >= 36 {
+			break
+		}
+	}
+
+	// Don't care about value, ought to be 0 anyhow.
+	t.Logf("i = %d", i)
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	trickItZero.fail()
+}
+
+// TestBreak1 should just work, with well-behaved iterators.
+// (The misbehaving iterator detector should not trigger.)
+func TestBreak1(t *testing.T) {
+	var result []int
+	var expect = []int{1, 2, -1, 1, 2, -2, 1, 2, -3}
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4}) {
+		if x == -4 {
+			break
+		}
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				break
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestBreak2 should just work, with well-behaved iterators.
+// (The misbehaving iterator detector should not trigger.)
+func TestBreak2(t *testing.T) {
+	var result []int
+	var expect = []int{1, 2, -1, 1, 2, -2, 1, 2, -3}
+outer:
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4}) {
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				break
+			}
+			if x == -4 {
+				break outer
+			}
+
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestContinue should just work, with well-behaved iterators.
+// (The misbehaving iterator detector should not trigger.)
+func TestContinue(t *testing.T) {
+	var result []int
+	var expect = []int{-1, 1, 2, -2, 1, 2, -3, 1, 2, -4}
+outer:
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4}) {
+		result = append(result, x)
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				continue outer
+			}
+			if x == -4 {
+				break outer
+			}
+
+			result = append(result, y)
+		}
+		result = append(result, x-10)
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestBreak3 should just work, with well-behaved iterators.
+// (The misbehaving iterator detector should not trigger.)
+func TestBreak3(t *testing.T) {
+	var result []int
+	var expect = []int{100, 10, 2, 4, 200, 10, 2, 4, 20, 2, 4, 300, 10, 2, 4, 20, 2, 4, 30}
+X:
+	for _, x := range OfSliceIndex([]int{100, 200, 300, 400}) {
+	Y:
+		for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+			if 10*y >= x {
+				break
+			}
+			result = append(result, y)
+			if y == 30 {
+				continue X
+			}
+		Z:
+			for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+				if z&1 == 1 {
+					continue Z
+				}
+				result = append(result, z)
+				if z >= 4 {
+					continue Y
+				}
+			}
+			result = append(result, -y) // should never be executed
+		}
+		result = append(result, x)
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestBreak1BadA should end in a panic when the outer-loop's
+// single-level break is ignore by BadOfSliceIndex
+func TestBreak1BadA(t *testing.T) {
+	var result []int
+	var expect = []int{1, 2, -1, 1, 2, -2, 1, 2, -3}
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	for _, x := range BadOfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		if x == -4 {
+			break
+		}
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				break
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+}
+
+// TestBreak1BadB should end in a panic, sooner, when the inner-loop's
+// (nested) single-level break is ignored by BadOfSliceIndex
+func TestBreak1BadB(t *testing.T) {
+	var result []int
+	var expect = []int{1, 2} // inner breaks, panics, after before outer appends
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		if x == -4 {
+			break
+		}
+		for _, y := range BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				break
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+}
+
+// TestMultiCont0 tests multilevel continue with no bad iterators
+// (it should just work)
+func TestMultiCont0(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4, 2000}
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range OfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						continue W // modified to be multilevel
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiCont1 tests multilevel continue with a bad iterator
+// in the outermost loop exited by the continue.
+func TestMultiCont1(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range BadOfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						continue W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiCont2 tests multilevel continue with a bad iterator
+// in a middle loop exited by the continue.
+func TestMultiCont2(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range OfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range BadOfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						continue W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiCont3 tests multilevel continue with a bad iterator
+// in the innermost loop exited by the continue.
+func TestMultiCont3(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range OfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						continue W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiBreak0 tests multilevel break with a bad iterator
+// in the outermost loop exited by the break (the outermost loop).
+func TestMultiBreak0(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range BadOfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range OfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						break W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiBreak1 tests multilevel break with a bad iterator
+// in an intermediate loop exited by the break.
+func TestMultiBreak1(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range BadOfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						break W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiBreak2 tests multilevel break with two bad iterators
+// in intermediate loops exited by the break.
+func TestMultiBreak2(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range BadOfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range BadOfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						break W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestMultiBreak3 tests multilevel break with the bad iterator
+// in the innermost loop exited by the break.
+func TestMultiBreak3(t *testing.T) {
+	var result []int
+	var expect = []int{1000, 10, 2, 4}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Errorf("Wanted to see a failure, result was %v", result)
+		}
+	}()
+
+W:
+	for _, w := range OfSliceIndex([]int{1000, 2000}) {
+		result = append(result, w)
+		if w == 2000 {
+			break
+		}
+		for _, x := range OfSliceIndex([]int{100, 200, 300, 400}) {
+			for _, y := range OfSliceIndex([]int{10, 20, 30, 40}) {
+				result = append(result, y)
+				for _, z := range BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+					if z&1 == 1 {
+						continue
+					}
+					result = append(result, z)
+					if z >= 4 {
+						break W
+					}
+				}
+				result = append(result, -y) // should never be executed
+			}
+			result = append(result, x)
+		}
+	}
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// veryBad tests that a loop nest behaves sensibly in the face of a
+// "very bad" iterator.  In this case, "sensibly" means that the
+// break out of X still occurs after the very bad iterator finally
+// quits running (the control flow bread crumbs remain.)
+func veryBad(s []int) []int {
+	var result []int
+X:
+	for _, x := range OfSliceIndex([]int{1, 2, 3}) {
+
+		result = append(result, x)
+
+		for _, y := range VeryBadOfSliceIndex(s) {
+			result = append(result, y)
+			break X
+		}
+		for _, z := range OfSliceIndex([]int{100, 200, 300}) {
+			result = append(result, z)
+			if z == 100 {
+				break
+			}
+		}
+	}
+	return result
+}
+
+// checkVeryBad wraps a "very bad" iterator with Check,
+// demonstrating that the very bad iterator also hides panics
+// thrown by Check.
+func checkVeryBad(s []int) []int {
+	var result []int
+X:
+	for _, x := range OfSliceIndex([]int{1, 2, 3}) {
+
+		result = append(result, x)
+
+		for _, y := range Check(VeryBadOfSliceIndex(s)) {
+			result = append(result, y)
+			break X
+		}
+		for _, z := range OfSliceIndex([]int{100, 200, 300}) {
+			result = append(result, z)
+			if z == 100 {
+				break
+			}
+		}
+	}
+	return result
+}
+
+// okay is the not-bad version of veryBad.
+// They should behave the same.
+func okay(s []int) []int {
+	var result []int
+X:
+	for _, x := range OfSliceIndex([]int{1, 2, 3}) {
+
+		result = append(result, x)
+
+		for _, y := range OfSliceIndex(s) {
+			result = append(result, y)
+			break X
+		}
+		for _, z := range OfSliceIndex([]int{100, 200, 300}) {
+			result = append(result, z)
+			if z == 100 {
+				break
+			}
+		}
+	}
+	return result
+}
+
+// TestVeryBad1 checks the behavior of an extremely poorly behaved iterator.
+func TestVeryBad1(t *testing.T) {
+	result := veryBad([]int{10, 20, 30, 40, 50}) // odd length
+	expect := []int{1, 10}
+
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestVeryBad2 checks the behavior of an extremely poorly behaved iterator.
+func TestVeryBad2(t *testing.T) {
+	result := veryBad([]int{10, 20, 30, 40}) // even length
+	expect := []int{1, 10}
+
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestCheckVeryBad checks the behavior of an extremely poorly behaved iterator,
+// which also suppresses the exceptions from "Check"
+func TestCheckVeryBad(t *testing.T) {
+	result := checkVeryBad([]int{10, 20, 30, 40}) // even length
+	expect := []int{1, 10}
+
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// TestOk is the nice version of the very bad iterator.
+func TestOk(t *testing.T) {
+	result := okay([]int{10, 20, 30, 40, 50}) // odd length
+	expect := []int{1, 10}
+
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+}
+
+// testBreak1BadDefer checks that defer behaves properly even in
+// the presence of loop bodies panicking out of bad iterators.
+// (i.e., the instrumentation did not break defer in these loops)
+func testBreak1BadDefer(t *testing.T) (result []int) {
+	var expect = []int{1, 2, -1, 1, 2, -2, 1, 2, -3, -30, -20, -10}
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Logf("Saw expected panic '%v'", r)
+			if !slices.Equal(expect, result) {
+				t.Errorf("(Inner) Expected %v, got %v", expect, result)
+			}
+		} else {
+			t.Error("Wanted to see a failure")
+		}
+	}()
+
+	for _, x := range BadOfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				break
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+	return
+}
+
+func TestBreak1BadDefer(t *testing.T) {
+	var result []int
+	var expect = []int{1, 2, -1, 1, 2, -2, 1, 2, -3, -30, -20, -10}
+	result = testBreak1BadDefer(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("(Outer) Expected %v, got %v", expect, result)
+	}
+}
+
+// testReturn1 has no bad iterators.
+func testReturn1(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				return
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+	return
+}
+
+// testReturn2 has an outermost bad iterator
+func testReturn2(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range BadOfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				return
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+	return
+}
+
+// testReturn3 has an innermost bad iterator
+func testReturn3(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				return
+			}
+			result = append(result, y)
+		}
+	}
+	return
+}
+
+// TestReturns checks that returns through bad iterators behave properly,
+// for inner and outer bad iterators.
+func TestReturns(t *testing.T) {
+	var result []int
+	var expect = []int{-1, 1, 2, -10}
+	var err any
+
+	result, err = testReturn1(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error %v", err)
+	}
+
+	result, err = testReturn2(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+	if err == nil {
+		t.Errorf("Missing expected error")
+	} else {
+		t.Logf("Saw expected panic '%v'", err)
+	}
+
+	result, err = testReturn3(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+	if err == nil {
+		t.Errorf("Missing expected error")
+	} else {
+		t.Logf("Saw expected panic '%v'", err)
+	}
+
+}
+
+// testGotoA1 tests loop-nest-internal goto, no bad iterators.
+func testGotoA1(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				goto A
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	A:
+	}
+	return
+}
+
+// testGotoA2 tests loop-nest-internal goto, outer bad iterator.
+func testGotoA2(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range BadOfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				goto A
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	A:
+	}
+	return
+}
+
+// testGotoA3 tests loop-nest-internal goto, inner bad iterator.
+func testGotoA3(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				goto A
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	A:
+	}
+	return
+}
+
+func TestGotoA(t *testing.T) {
+	var result []int
+	var expect = []int{-1, 1, 2, -2, 1, 2, -3, 1, 2, -4, -30, -20, -10}
+	var expect3 = []int{-1, 1, 2, -10} // first goto becomes a panic
+	var err any
+
+	result, err = testGotoA1(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error %v", err)
+	}
+
+	result, err = testGotoA2(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+	if err == nil {
+		t.Errorf("Missing expected error")
+	} else {
+		t.Logf("Saw expected panic '%v'", err)
+	}
+
+	result, err = testGotoA3(t)
+	if !slices.Equal(expect3, result) {
+		t.Errorf("Expected %v, got %v", expect3, result)
+	}
+	if err == nil {
+		t.Errorf("Missing expected error")
+	} else {
+		t.Logf("Saw expected panic '%v'", err)
+	}
+}
+
+// testGotoB1 tests loop-nest-exiting goto, no bad iterators.
+func testGotoB1(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				goto B
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+B:
+	result = append(result, 999)
+	return
+}
+
+// testGotoB2 tests loop-nest-exiting goto, outer bad iterator.
+func testGotoB2(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range BadOfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range OfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				goto B
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+B:
+	result = append(result, 999)
+	return
+}
+
+// testGotoB3 tests loop-nest-exiting goto, inner bad iterator.
+func testGotoB3(t *testing.T) (result []int, err any) {
+	defer func() {
+		err = recover()
+	}()
+	for _, x := range OfSliceIndex([]int{-1, -2, -3, -4, -5}) {
+		result = append(result, x)
+		if x == -4 {
+			break
+		}
+		defer func() {
+			result = append(result, x*10)
+		}()
+		for _, y := range BadOfSliceIndex([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}) {
+			if y == 3 {
+				goto B
+			}
+			result = append(result, y)
+		}
+		result = append(result, x)
+	}
+B:
+	result = append(result, 999)
+	return
+}
+
+func TestGotoB(t *testing.T) {
+	var result []int
+	var expect = []int{-1, 1, 2, 999, -10}
+	var expectX = []int{-1, 1, 2, -10}
+	var err any
+
+	result, err = testGotoB1(t)
+	if !slices.Equal(expect, result) {
+		t.Errorf("Expected %v, got %v", expect, result)
+	}
+	if err != nil {
+		t.Errorf("Unexpected error %v", err)
+	}
+
+	result, err = testGotoB2(t)
+	if !slices.Equal(expectX, result) {
+		t.Errorf("Expected %v, got %v", expectX, result)
+	}
+	if err == nil {
+		t.Errorf("Missing expected error")
+	} else {
+		t.Logf("Saw expected panic '%v'", err)
+	}
+
+	result, err = testGotoB3(t)
+	if !slices.Equal(expectX, result) {
+		t.Errorf("Expected %v, got %v", expectX, result)
+	}
+	if err == nil {
+		t.Errorf("Missing expected error")
+	} else {
+		t.Logf("Saw expected panic '%v'", err)
+	}
+}