Add a shim for internal/fuzz

This simply shadows the real code temporarily to see what else is
broken. It only defines a single type to fix testing/internal/testdeps.

5 files changed, 308 insertions, 9 deletions

diff --git a/src/internal/fuzz/fuzz.go b/src/internal/fuzz/fuzz.go
new file mode 100644
index 000000000..ee6e0544b
--- /dev/null
+++ b/src/internal/fuzz/fuzz.go
@@ -0,0 +1,133 @@
+// Package fuzz is a shim to allow compilation against Go 1.18.
+// It only defines a single type to work with testing/internal/testdeps,
+// and hide all the other new dependencies from this package.
+package fuzz
+
+import (
+	"context"
+	"errors"
+	"io"
+	"reflect"
+	"time"
+)
+
+// CorpusEntry represents an individual input for fuzzing.
+//
+// We must use an equivalent type in the testing and testing/internal/testdeps
+// packages, but testing can't import this package directly, and we don't want
+// to export this type from testing. Instead, we use the same struct type and
+// use a type alias (not a defined type) for convenience.
+type CorpusEntry = struct {
+	Parent string
+
+	// Path is the path of the corpus file, if the entry was loaded from disk.
+	// For other entries, including seed values provided by f.Add, Path is the
+	// name of the test, e.g. seed#0 or its hash.
+	Path string
+
+	// Data is the raw input data. Data should only be populated for seed
+	// values. For on-disk corpus files, Data will be nil, as it will be loaded
+	// from disk using Path.
+	Data []byte
+
+	// Values is the unmarshaled values from a corpus file.
+	Values []any
+
+	Generation int
+
+	// IsSeed indicates whether this entry is part of the seed corpus.
+	IsSeed bool
+}
+
+// CoordinateFuzzingOpts is a set of arguments for CoordinateFuzzing.
+// The zero value is valid for each field unless specified otherwise.
+type CoordinateFuzzingOpts struct {
+	// Log is a writer for logging progress messages and warnings.
+	// If nil, io.Discard will be used instead.
+	Log io.Writer
+
+	// Timeout is the amount of wall clock time to spend fuzzing after the corpus
+	// has loaded. If zero, there will be no time limit.
+	Timeout time.Duration
+
+	// Limit is the number of random values to generate and test. If zero,
+	// there will be no limit on the number of generated values.
+	Limit int64
+
+	// MinimizeTimeout is the amount of wall clock time to spend minimizing
+	// after discovering a crasher. If zero, there will be no time limit. If
+	// MinimizeTimeout and MinimizeLimit are both zero, then minimization will
+	// be disabled.
+	MinimizeTimeout time.Duration
+
+	// MinimizeLimit is the maximum number of calls to the fuzz function to be
+	// made while minimizing after finding a crash. If zero, there will be no
+	// limit. Calls to the fuzz function made when minimizing also count toward
+	// Limit. If MinimizeTimeout and MinimizeLimit are both zero, then
+	// minimization will be disabled.
+	MinimizeLimit int64
+
+	// parallel is the number of worker processes to run in parallel. If zero,
+	// CoordinateFuzzing will run GOMAXPROCS workers.
+	Parallel int
+
+	// Seed is a list of seed values added by the fuzz target with testing.F.Add
+	// and in testdata.
+	Seed []CorpusEntry
+
+	// Types is the list of types which make up a corpus entry.
+	// Types must be set and must match values in Seed.
+	Types []reflect.Type
+
+	// CorpusDir is a directory where files containing values that crash the
+	// code being tested may be written. CorpusDir must be set.
+	CorpusDir string
+
+	// CacheDir is a directory containing additional "interesting" values.
+	// The fuzzer may derive new values from these, and may write new values here.
+	CacheDir string
+}
+
+// CoordinateFuzzing creates several worker processes and communicates with
+// them to test random inputs that could trigger crashes and expose bugs.
+// The worker processes run the same binary in the same directory with the
+// same environment variables as the coordinator process. Workers also run
+// with the same arguments as the coordinator, except with the -test.fuzzworker
+// flag prepended to the argument list.
+//
+// If a crash occurs, the function will return an error containing information
+// about the crash, which can be reported to the user.
+func CoordinateFuzzing(ctx context.Context, opts CoordinateFuzzingOpts) (err error) {
+	return errors.New("not implemented")
+}
+
+// ReadCorpus reads the corpus from the provided dir. The returned corpus
+// entries are guaranteed to match the given types. Any malformed files will
+// be saved in a MalformedCorpusError and returned, along with the most recent
+// error.
+func ReadCorpus(dir string, types []reflect.Type) ([]CorpusEntry, error) {
+	return nil, errors.New("not implemented")
+}
+
+// CheckCorpus verifies that the types in vals match the expected types
+// provided.
+func CheckCorpus(vals []any, types []reflect.Type) error {
+	return errors.New("not implemented")
+}
+
+func ResetCoverage() {}
+func SnapshotCoverage() {}
+
+// RunFuzzWorker is called in a worker process to communicate with the
+// coordinator process in order to fuzz random inputs. RunFuzzWorker loops
+// until the coordinator tells it to stop.
+//
+// fn is a wrapper on the fuzz function. It may return an error to indicate
+// a given input "crashed". The coordinator will also record a crasher if
+// the function times out or terminates the process.
+//
+// RunFuzzWorker returns an error if it could not communicate with the
+// coordinator process.
+func RunFuzzWorker(ctx context.Context, fn func(CorpusEntry) error) error {
+	return errors.New("not implemented")
+}
diff --git a/src/testing/fuzz.go b/src/testing/fuzz.go
new file mode 100644
index 000000000..76ad6d945
--- /dev/null
+++ b/src/testing/fuzz.go
@@ -0,0 +1,143 @@
+package testing
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"time"
+)
+
+// InternalFuzzTarget is an internal type but exported because it is
+// cross-package; it is part of the implementation of the "go test" command.
+type InternalFuzzTarget struct {
+	Name string
+	Fn   func(f *F)
+}
+
+// F is a type passed to fuzz tests.
+//
+// Fuzz tests run generated inputs against a provided fuzz target, which can
+// find and report potential bugs in the code being tested.
+//
+// A fuzz test runs the seed corpus by default, which includes entries provided
+// by (*F).Add and entries in the testdata/fuzz/<FuzzTestName> directory. After
+// any necessary setup and calls to (*F).Add, the fuzz test must then call
+// (*F).Fuzz to provide the fuzz target. See the testing package documentation
+// for an example, and see the F.Fuzz and F.Add method documentation for
+// details.
+//
+// *F methods can only be called before (*F).Fuzz. Once the test is
+// executing the fuzz target, only (*T) methods can be used. The only *F methods
+// that are allowed in the (*F).Fuzz function are (*F).Failed and (*F).Name.
+type F struct {
+	common
+	fuzzContext *fuzzContext
+	testContext *testContext
+
+	// inFuzzFn is true when the fuzz function is running. Most F methods cannot
+	// be called when inFuzzFn is true.
+	inFuzzFn bool
+
+	// corpus is a set of seed corpus entries, added with F.Add and loaded
+	// from testdata.
+	corpus []corpusEntry
+
+	result     fuzzResult
+	fuzzCalled bool
+}
+
+// corpusEntry is an alias to the same type as internal/fuzz.CorpusEntry.
+// We use a type alias because we don't want to export this type, and we can't
+// import internal/fuzz from testing.
+type corpusEntry = struct {
+	Parent     string
+	Path       string
+	Data       []byte
+	Values     []interface{}
+	Generation int
+	IsSeed     bool
+}
+
+// Add will add the arguments to the seed corpus for the fuzz test. This will be
+// a no-op if called after or within the fuzz target, and args must match the
+// arguments for the fuzz target.
+func (f *F) Add(args ...interface{}) {
+	var values []interface{}
+	for i := range args {
+		if t := reflect.TypeOf(args[i]); !supportedTypes[t] {
+			panic(fmt.Sprintf("testing: unsupported type to Add %v", t))
+		}
+		values = append(values, args[i])
+	}
+	f.corpus = append(f.corpus, corpusEntry{Values: values, IsSeed: true, Path: fmt.Sprintf("seed#%d", len(f.corpus))})
+}
+
+// supportedTypes represents all of the supported types which can be fuzzed.
+var supportedTypes = map[reflect.Type]bool{
+	reflect.TypeOf(([]byte)("")):  true,
+	reflect.TypeOf((string)("")):  true,
+	reflect.TypeOf((bool)(false)): true,
+	reflect.TypeOf((byte)(0)):     true,
+	reflect.TypeOf((rune)(0)):     true,
+	reflect.TypeOf((float32)(0)):  true,
+	reflect.TypeOf((float64)(0)):  true,
+	reflect.TypeOf((int)(0)):      true,
+	reflect.TypeOf((int8)(0)):     true,
+	reflect.TypeOf((int16)(0)):    true,
+	reflect.TypeOf((int32)(0)):    true,
+	reflect.TypeOf((int64)(0)):    true,
+	reflect.TypeOf((uint)(0)):     true,
+	reflect.TypeOf((uint8)(0)):    true,
+	reflect.TypeOf((uint16)(0)):   true,
+	reflect.TypeOf((uint32)(0)):   true,
+	reflect.TypeOf((uint64)(0)):   true,
+}
+
+// Fuzz runs the fuzz function, ff, for fuzz testing. If ff fails for a set of
+// arguments, those arguments will be added to the seed corpus.
+//
+// ff must be a function with no return value whose first argument is *T and
+// whose remaining arguments are the types to be fuzzed.
+// For example:
+//
+//     f.Fuzz(func(t *testing.T, b []byte, i int) { ... })
+//
+// The following types are allowed: []byte, string, bool, byte, rune, float32,
+// float64, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64.
+// More types may be supported in the future.
+//
+// ff must not call any *F methods, e.g. (*F).Log, (*F).Error, (*F).Skip. Use
+// the corresponding *T method instead. The only *F methods that are allowed in
+// the (*F).Fuzz function are (*F).Failed and (*F).Name.
+//
+// This function should be fast and deterministic, and its behavior should not
+// depend on shared state. No mutatable input arguments, or pointers to them,
+// should be retained between executions of the fuzz function, as the memory
+// backing them may be mutated during a subsequent invocation. ff must not
+// modify the underlying data of the arguments provided by the fuzzing engine.
+//
+// When fuzzing, F.Fuzz does not return until a problem is found, time runs out
+// (set with -fuzztime), or the test process is interrupted by a signal. F.Fuzz
+// should be called exactly once, unless F.Skip or F.Fail is called beforehand.
+func (f *F) Fuzz(ff interface{}) {
+	f.failed = true
+	f.result.N = 0
+	f.result.T = 0
+	f.result.Error = errors.New("operation not implemented")
+	return
+}
+
+// fuzzContext holds fields common to all fuzz tests.
+type fuzzContext struct {
+	deps testDeps
+	mode fuzzMode
+}
+
+type fuzzMode uint8
+
+// fuzzResult contains the results of a fuzz run.
+type fuzzResult struct {
+	N     int           // The number of iterations.
+	T     time.Duration // The total time taken.
+	Error error         // Error is the error from the failing input
+}
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 243632354..045ee5beb 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -430,15 +430,6 @@ type testDeps interface {
 	MatchString(pat, str string) (bool, error)
 }
 
-func MainStart(deps interface{}, tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) *M {
-	Init()
-	return &M{
-		Tests:      tests,
-		Benchmarks: benchmarks,
-		deps:       deps.(testDeps),
-	}
-}
-
 // Run runs the tests. It returns an exit code to pass to os.Exit.
 func (m *M) Run() (code int) {
 	defer func() {
diff --git a/src/testing/testing_go118.go b/src/testing/testing_go118.go
new file mode 100644
index 000000000..1c2c835be
--- /dev/null
+++ b/src/testing/testing_go118.go
@@ -0,0 +1,16 @@
+//go:build go1.18
+// +build go1.18
+
+package testing
+
+// MainStart is meant for use by tests generated by 'go test'.
+// It is not meant to be called directly and is not subject to the Go 1 compatibility document.
+// It may change signature from release to release.
+func MainStart(deps interface{}, tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) *M {
+	Init()
+	return &M{
+		Tests:      tests,
+		Benchmarks: benchmarks,
+		deps:       deps.(testDeps),
+	}
+}
diff --git a/src/testing/testing_other.go b/src/testing/testing_other.go
new file mode 100644
index 000000000..875115e96
--- /dev/null
+++ b/src/testing/testing_other.go
@@ -0,0 +1,16 @@
+//go:build !go1.18
+// +build !go1.18
+
+package testing
+
+// MainStart is meant for use by tests generated by 'go test'.
+// It is not meant to be called directly and is not subject to the Go 1 compatibility document.
+// It may change signature from release to release.
+func MainStart(deps interface{}, tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) *M {
+	Init()
+	return &M{
+		Tests:      tests,
+		Benchmarks: benchmarks,
+		deps:       deps.(testDeps),
+	}
+}