--- /dev/null
+// 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.
+
+// Bisect finds changes responsible for causing a failure.
+// A typical use is to identify the source locations in a program
+// that are miscompiled by a given compiler optimization.
+//
+// Usage:
+//
+// bisect [flags] [var=value...] command [arguments...]
+//
+// Bisect operates on a target command line – the target – that can be
+// run with various changes individually enabled or disabled. With none
+// of the changes enabled, the target is known to succeed (exit with exit
+// code zero). With all the changes enabled, the target is known to fail
+// (exit any other way). Bisect repeats the target with different sets of
+// changes enabled, using binary search to find (non-overlapping) minimal
+// change sets that preserve the failure.
+//
+// The target must cooperate with bisect by accepting a change pattern
+// and then enabling and reporting the changes that match that pattern.
+// The change pattern is passed to the target by substituting it anywhere
+// the string PATTERN appears in the environment values or the command
+// arguments. For each change that matches the pattern, the target must
+// enable that change and also print one or more “match lines”
+// (to standard output or standard error) describing the change.
+// The [golang.org/x/tools/internal/bisect] package provides functions to help
+// targets implement this protocol. We plan to publish that package
+// in a non-internal location after finalizing its API.
+//
+// # Command Line Flags
+//
+// Bisect supports the following command-line flags:
+//
+// -max M
+//
+// Stop after finding M minimal change sets. The default is no maximum, meaning to run until
+// all changes that provoke a failure have been identified.
+//
+// -maxset S
+//
+// Disallow change sets larger than S elements. The default is no maximum.
+//
+// -timeout D
+//
+// If the target runs for longer than duration D, stop the target and interpret that as a failure.
+// The default is no timeout.
+//
+// -count N
+//
+// Run each trial N times (default 2), checking for consistency.
+//
+// -v
+//
+// Print verbose output, showing each run and its match lines.
+//
+// # Example
+//
+// For example, the Go compiler can be used as a bisect target to
+// determine the source locations that cause a test failure when compiled with
+// a new optimization:
+//
+// bisect go test -gcflags=all=-d=loopvarhash=PATTERN
+//
+// The -gcflags=all= instructs the go command to pass the -d=... to the Go compiler
+// when compiling all packages. Bisect replaces the literal text “PATTERN” with a specific pattern
+// on each invocation, varying the patterns to determine the minimal set of changes
+// needed to reproduce the failure.
+//
+// # Defeating Build Caches
+//
+// Build systems cache build results, to avoid repeating the same compilations
+// over and over. When using a cached build result, the go command (correctly)
+// reprints the cached standard output and standard error associated with that
+// command invocation. (This makes commands like 'go build -gcflags=-S' for
+// printing an assembly listing work reliably.)
+//
+// Unfortunately, most build systems, including Bazel, are not as careful
+// as the go command about reprinting compiler output. If the compiler is
+// what prints match lines, a build system that suppresses compiler
+// output when using cached compiler results will confuse bisect.
+// To defeat such build caches, bisect replaces the literal text “RANDOM”
+// in environment values and command arguments with a random 64-bit value
+// during each invocation. The Go compiler conveniently accepts a
+// -d=ignore=... debug flag that ignores its argument, so to run the
+// previous example using Bazel, the invocation is:
+//
+// bazel test --define=gc_goopts=-d=loopvarhash=PATTERN,unused=RANDOM //path/to:test
+package main
+
+import (
+ "context"
+ "flag"
+ "fmt"
+ "io"
+ "log"
+ "math/rand"
+ "os"
+ "os/exec"
+ "strconv"
+ "strings"
+ "time"
+
+ "golang.org/x/tools/internal/bisect"
+)
+
+// Preserve import of bisect, to allow [bisect.Match] in the doc comment.
+var _ bisect.Matcher
+
+func usage() {
+ fmt.Fprintf(os.Stderr, "usage: bisect [flags] [var=value...] command [arguments...]\n")
+ flag.PrintDefaults()
+ os.Exit(2)
+}
+
+func main() {
+ log.SetFlags(0)
+ log.SetPrefix("bisect: ")
+
+ var b Bisect
+ b.Stdout = os.Stdout
+ b.Stderr = os.Stderr
+ flag.IntVar(&b.Max, "max", 0, "stop after finding `m` failing change sets")
+ flag.IntVar(&b.MaxSet, "maxset", 0, "do not search for change sets larger than `s` elements")
+ flag.DurationVar(&b.Timeout, "timeout", 0, "stop target and consider failed after duration `d`")
+ flag.IntVar(&b.Count, "count", 2, "run target `n` times for each trial")
+ flag.BoolVar(&b.Verbose, "v", false, "enable verbose output")
+
+ flag.Usage = usage
+ flag.Parse()
+ args := flag.Args()
+
+ // Split command line into env settings, command name, args.
+ i := 0
+ for i < len(args) && strings.Contains(args[i], "=") {
+ i++
+ }
+ if i == len(args) {
+ usage()
+ }
+ b.Env, b.Cmd, b.Args = args[:i], args[i], args[i+1:]
+ if !b.Search() {
+ os.Exit(1)
+ }
+}
+
+// A Bisect holds the state for a bisect invocation.
+type Bisect struct {
+ // Env is the additional environment variables for the command.
+ // PATTERN and RANDOM are substituted in the values, but not the names.
+ Env []string
+
+ // Cmd is the command (program name) to run.
+ // PATTERN and RANDOM are not substituted.
+ Cmd string
+
+ // Args is the command arguments.
+ // PATTERN and RANDOM are substituted anywhere they appear.
+ Args []string
+
+ // Command-line flags controlling bisect behavior.
+ Max int // maximum number of sets to report (0 = unlimited)
+ MaxSet int // maximum number of elements in a set (0 = unlimited)
+ Timeout time.Duration // kill target and assume failed after this duration (0 = unlimited)
+ Count int // run target this many times for each trial and give up if flaky (min 1 assumed; default 2 on command line set in main)
+ Verbose bool // print long output about each trial (only useful for debugging bisect itself)
+
+ // State for running bisect, replaced during testing.
+ // Failing change sets are printed to Stdout; all other output goes to Stderr.
+ Stdout io.Writer // where to write standard output (usually os.Stdout)
+ Stderr io.Writer // where to write standard error (usually os.Stderr)
+ TestRun func(env []string, cmd string, args []string) (out []byte, err error) // if non-nil, used instead of exec.Command
+
+ // State maintained by Search.
+
+ // By default, Search looks for a minimal set of changes that cause a failure when enabled.
+ // If Disable is true, the search is inverted and seeks a minimal set of changes that
+ // cause a failure when disabled. In this case, the search proceeds as normal except that
+ // each pattern starts with a !.
+ Disable bool
+
+ // Add is a list of suffixes to add to every trial, because they
+ // contain changes that are necessary for a group we are assembling.
+ Add []string
+
+ // Skip is a list of suffixes that uniquely identify changes to exclude from every trial,
+ // because they have already been used in failing change sets.
+ // Suffixes later in the list may only be unique after removing
+ // the ones earlier in the list.
+ // Skip applies after Add.
+ Skip []string
+}
+
+// A Result holds the result of a single target trial.
+type Result struct {
+ Success bool // whether the target succeeded (exited with zero status)
+ Cmd string // full target command line
+ Out string // full target output (stdout and stderr combined)
+
+ Suffix string // the suffix used for collecting MatchIDs, MatchText, and MatchFull
+ MatchIDs []uint64 // match IDs enabled during this trial
+ MatchText []string // match reports for the IDs, with match markers removed
+ MatchFull []string // full match lines for the IDs, with match markers kept
+}
+
+// &searchFatal is a special panic value to signal that Search failed.
+// This lets us unwind the search recursion on a fatal error
+// but have Search return normally.
+var searchFatal int
+
+// Search runs a bisect search according to the configuration in b.
+// It reports whether any failing change sets were found.
+func (b *Bisect) Search() bool {
+ defer func() {
+ // Recover from panic(&searchFatal), implicitly returning false from Search.
+ // Re-panic on any other panic.
+ if e := recover(); e != nil && e != &searchFatal {
+ panic(e)
+ }
+ }()
+
+ // Run with no changes and all changes, to figure out which direction we're searching.
+ // The goal is to find the minimal set of changes to toggle
+ // starting with the state where everything works.
+ // If "no changes" succeeds and "all changes" fails,
+ // we're looking for a minimal set of changes to enable to provoke the failure
+ // (broken = runY, b.Negate = false)
+ // If "no changes" fails and "all changes" succeeds,
+ // we're looking for a minimal set of changes to disable to provoke the failure
+ // (broken = runN, b.Negate = true).
+
+ b.Logf("checking target with all changes disabled")
+ runN := b.Run("n")
+
+ b.Logf("checking target with all changes enabled")
+ runY := b.Run("y")
+
+ var broken *Result
+ switch {
+ case runN.Success && !runY.Success:
+ b.Logf("target succeeds with no changes, fails with all changes")
+ b.Logf("searching for minimal set of enabled changes causing failure")
+ broken = runY
+ b.Disable = false
+
+ case !runN.Success && runY.Success:
+ b.Logf("target fails with no changes, succeeds with all changes")
+ b.Logf("searching for minimal set of disabled changes causing failure")
+ broken = runN
+ b.Disable = true
+
+ case runN.Success && runY.Success:
+ b.Fatalf("target succeeds with no changes and all changes")
+
+ case !runN.Success && !runY.Success:
+ b.Fatalf("target fails with no changes and all changes")
+ }
+
+ // Loop finding and printing change sets, until none remain.
+ found := 0
+ for {
+ // Find set.
+ bad := b.search(broken)
+ if bad == nil {
+ if found == 0 {
+ b.Fatalf("cannot find any failing change sets of size ≤ %d", b.MaxSet)
+ }
+ break
+ }
+
+ // Confirm that set really does fail, to avoid false accusations.
+ // Also asking for user-visible output; earlier runs did not.
+ b.Logf("confirming failing change set")
+ b.Add = append(b.Add[:0], bad...)
+ broken = b.Run("v")
+ if broken.Success {
+ b.Logf("confirmation run succeeded unexpectedly")
+ }
+ b.Add = b.Add[:0]
+
+ // Print confirmed change set.
+ found++
+ b.Logf("FOUND failing change set")
+ desc := "(enabling changes causes failure)"
+ if b.Disable {
+ desc = "(disabling changes causes failure)"
+ }
+ fmt.Fprintf(b.Stdout, "--- change set #%d %s\n%s\n---\n", found, desc, strings.Join(broken.MatchText, "\n"))
+
+ // Stop if we've found enough change sets.
+ if b.Max > 0 && found >= b.Max {
+ break
+ }
+
+ // If running bisect target | tee bad.txt, prints to stdout and stderr
+ // both appear on the terminal, but the ones to stdout go through tee
+ // and can take a little bit of extra time. Sleep 1 millisecond to give
+ // tee time to catch up, so that its stdout print does not get interlaced
+ // with the stderr print from the next b.Log message.
+ time.Sleep(1 * time.Millisecond)
+
+ // Disable the now-known-bad changes and see if any failures remain.
+ b.Logf("checking for more failures")
+ b.Skip = append(bad, b.Skip...)
+ broken = b.Run("")
+ if broken.Success {
+ what := "enabled"
+ if b.Disable {
+ what = "disabled"
+ }
+ b.Logf("target succeeds with all remaining changes %s", what)
+ break
+ }
+ b.Logf("target still fails; searching for more bad changes")
+ }
+ return true
+}
+
+// Fatalf prints a message to standard error and then panics,
+// causing Search to return false.
+func (b *Bisect) Fatalf(format string, args ...any) {
+ s := fmt.Sprintf("bisect: fatal error: "+format, args...)
+ if !strings.HasSuffix(s, "\n") {
+ s += "\n"
+ }
+ b.Stderr.Write([]byte(s))
+ panic(&searchFatal)
+}
+
+// Logf prints a message to standard error.
+func (b *Bisect) Logf(format string, args ...any) {
+ s := fmt.Sprintf("bisect: "+format, args...)
+ if !strings.HasSuffix(s, "\n") {
+ s += "\n"
+ }
+ b.Stderr.Write([]byte(s))
+}
+
+// search searches for a single locally minimal change set.
+//
+// Invariant: r describes the result of r.Suffix + b.Add, which failed.
+// (There's an implicit -b.Skip everywhere here. b.Skip does not change.)
+// We want to extend r.Suffix to preserve the failure, working toward
+// a suffix that identifies a single change.
+func (b *Bisect) search(r *Result) []string {
+ // The caller should be passing in a failure result that we diagnose.
+ if r.Success {
+ b.Fatalf("internal error: unexpected success") // mistake by caller
+ }
+
+ // If the failure reported no changes, the target is misbehaving.
+ if len(r.MatchIDs) == 0 {
+ b.Fatalf("failure with no reported changes:\n\n$ %s\n%s\n", r.Cmd, r.Out)
+ }
+
+ // If there's one matching change, that's the one we're looking for.
+ if len(r.MatchIDs) == 1 {
+ if r.Suffix == "" {
+ return []string{"y"}
+ }
+ return []string{r.Suffix}
+ }
+
+ // If the suffix we were tracking in the trial is already 64 bits,
+ // either the target is bad or bisect itself is buggy.
+ if len(r.Suffix) >= 64 {
+ b.Fatalf("failed to isolate a single change with very long suffix")
+ }
+
+ // We want to split the current matchIDs by left-extending the suffix with 0 and 1.
+ // If all the matches have the same next bit, that won't cause a split, which doesn't
+ // break the algorithm but does waste time. Avoid wasting time by left-extending
+ // the suffix to the longest suffix shared by all the current match IDs
+ // before adding 0 or 1.
+ suffix := commonSuffix(r.MatchIDs)
+ if !strings.HasSuffix(suffix, r.Suffix) {
+ b.Fatalf("internal error: invalid common suffix") // bug in commonSuffix
+ }
+
+ // Run 0suffix and 1suffix. If one fails, chase down the failure in that half.
+ r0 := b.Run("0" + suffix)
+ if !r0.Success {
+ return b.search(r0)
+ }
+ r1 := b.Run("1" + suffix)
+ if !r1.Success {
+ return b.search(r1)
+ }
+
+ // suffix failed, but 0suffix and 1suffix succeeded.
+ // Assuming the target isn't flaky, this means we need
+ // at least one change from 0suffix AND at least one from 1suffix.
+ // We are already tracking N = len(b.Add) other changes and are
+ // allowed to build sets of size at least 1+N (or we shouldn't be here at all).
+ // If we aren't allowed to build sets of size 2+N, give up this branch.
+ if b.MaxSet > 0 && 2+len(b.Add) > b.MaxSet {
+ return nil
+ }
+
+ // Adding all matches for 1suffix, recurse to narrow down 0suffix.
+ old := len(b.Add)
+ b.Add = append(b.Add, "1"+suffix)
+ r0 = b.Run("0" + suffix)
+ if r0.Success {
+ // 0suffix + b.Add + 1suffix = suffix + b.Add is what r describes, and it failed.
+ b.Fatalf("target fails inconsistently")
+ }
+ bad0 := b.search(r0)
+ if bad0 == nil {
+ // Search failed due to MaxSet limit.
+ return nil
+ }
+ b.Add = b.Add[:old]
+
+ // Adding the specific match we found in 0suffix, recurse to narrow down 1suffix.
+ b.Add = append(b.Add[:old], bad0...)
+ r1 = b.Run("1" + suffix)
+ if r1.Success {
+ // 1suffix + b.Add + bad0 = bad0 + b.Add + 1suffix is what b.search(r0) reported as a failure.
+ b.Fatalf("target fails inconsistently")
+ }
+ bad1 := b.search(r1)
+ if bad1 == nil {
+ // Search failed due to MaxSet limit.
+ return nil
+ }
+ b.Add = b.Add[:old]
+
+ // bad0 and bad1 together provoke the failure.
+ return append(bad0, bad1...)
+}
+
+// Run runs a set of trials selecting changes with the given suffix,
+// plus the ones in b.Add and not the ones in b.Skip.
+// The returned result's MatchIDs, MatchText, and MatchFull
+// only list the changes that match suffix.
+// When b.Count > 1, Run runs b.Count trials and requires
+// that they all succeed or they all fail. If not, it calls b.Fatalf.
+func (b *Bisect) Run(suffix string) *Result {
+ out := b.run(suffix)
+ for i := 1; i < b.Count; i++ {
+ r := b.run(suffix)
+ if r.Success != out.Success {
+ b.Fatalf("target fails inconsistently")
+ }
+ }
+ return out
+}
+
+// run runs a single trial for Run.
+func (b *Bisect) run(suffix string) *Result {
+ random := fmt.Sprint(rand.Uint64())
+
+ // Accept suffix == "v" to mean we need user-visible output.
+ visible := ""
+ if suffix == "v" {
+ visible = "v"
+ suffix = ""
+ }
+
+ // Construct change ID pattern.
+ var pattern string
+ if suffix == "y" || suffix == "n" {
+ pattern = suffix
+ suffix = ""
+ } else {
+ var elem []string
+ if suffix != "" {
+ elem = append(elem, "+", suffix)
+ }
+ for _, x := range b.Add {
+ elem = append(elem, "+", x)
+ }
+ for _, x := range b.Skip {
+ elem = append(elem, "-", x)
+ }
+ pattern = strings.Join(elem, "")
+ if pattern == "" {
+ pattern = "y"
+ }
+ }
+ if b.Disable {
+ pattern = "!" + pattern
+ }
+ pattern = visible + pattern
+
+ // Construct substituted env and args.
+ env := make([]string, len(b.Env))
+ for i, x := range b.Env {
+ k, v, _ := strings.Cut(x, "=")
+ env[i] = k + "=" + replace(v, pattern, random)
+ }
+ args := make([]string, len(b.Args))
+ for i, x := range b.Args {
+ args[i] = replace(x, pattern, random)
+ }
+
+ // Construct and log command line.
+ // There is no newline in the log print.
+ // The line will be completed when the command finishes.
+ cmdText := strings.Join(append(append(env, b.Cmd), args...), " ")
+ fmt.Fprintf(b.Stderr, "bisect: run: %s...", cmdText)
+
+ // Run command with args and env.
+ var out []byte
+ var err error
+ if b.TestRun != nil {
+ out, err = b.TestRun(env, b.Cmd, args)
+ } else {
+ ctx := context.Background()
+ if b.Timeout != 0 {
+ var cancel context.CancelFunc
+ ctx, cancel = context.WithTimeout(ctx, b.Timeout)
+ defer cancel()
+ }
+ cmd := exec.CommandContext(ctx, b.Cmd, args...)
+ cmd.Env = append(os.Environ(), env...)
+ // Set up cmd.Cancel, cmd.WaitDelay on Go 1.20 and later
+ // TODO(rsc): Inline go120.go's cmdInterrupt once we stop supporting Go 1.19.
+ cmdInterrupt(cmd)
+ out, err = cmd.CombinedOutput()
+ }
+
+ // Parse output to construct result.
+ r := &Result{
+ Suffix: suffix,
+ Success: err == nil,
+ Cmd: cmdText,
+ Out: string(out),
+ }
+
+ // Calculate bits, mask to identify suffix matches.
+ var bits, mask uint64
+ if suffix != "" && suffix != "y" && suffix != "n" && suffix != "v" {
+ var err error
+ bits, err = strconv.ParseUint(suffix, 2, 64)
+ if err != nil {
+ b.Fatalf("internal error: bad suffix")
+ }
+ mask = uint64(1<<len(suffix)) - 1
+ }
+
+ // Process output, collecting match reports for suffix.
+ have := make(map[uint64]bool)
+ all := r.Out
+ for all != "" {
+ var line string
+ line, all, _ = strings.Cut(all, "\n")
+ short, id, ok := bisect.CutMarker(line)
+ if !ok || (id&mask) != bits {
+ continue
+ }
+
+ if !have[id] {
+ have[id] = true
+ r.MatchIDs = append(r.MatchIDs, id)
+ }
+ r.MatchText = append(r.MatchText, short)
+ r.MatchFull = append(r.MatchFull, line)
+ }
+
+ // Finish log print from above, describing the command's completion.
+ if err == nil {
+ fmt.Fprintf(b.Stderr, " ok (%d matches)\n", len(r.MatchIDs))
+ } else {
+ fmt.Fprintf(b.Stderr, " FAIL (%d matches)\n", len(r.MatchIDs))
+ }
+
+ if err != nil && len(r.MatchIDs) == 0 {
+ b.Fatalf("target failed without printing any matches\n%s", r.Out)
+ }
+
+ // In verbose mode, print extra debugging: all the lines with match markers.
+ if b.Verbose {
+ b.Logf("matches:\n%s", strings.Join(r.MatchFull, "\n\t"))
+ }
+
+ return r
+}
+
+// replace returns x with literal text PATTERN and RANDOM replaced by pattern and random.
+func replace(x, pattern, random string) string {
+ x = strings.ReplaceAll(x, "PATTERN", pattern)
+ x = strings.ReplaceAll(x, "RANDOM", random)
+ return x
+}
+
+// commonSuffix returns the longest common binary suffix shared by all uint64s in list.
+// If list is empty, commonSuffix returns an empty string.
+func commonSuffix(list []uint64) string {
+ if len(list) == 0 {
+ return ""
+ }
+ b := list[0]
+ n := 64
+ for _, x := range list {
+ for x&((1<<n)-1) != b {
+ n--
+ b &= (1 << n) - 1
+ }
+ }
+ s := make([]byte, n)
+ for i := n - 1; i >= 0; i-- {
+ s[i] = '0' + byte(b&1)
+ b >>= 1
+ }
+ return string(s[:])
+}
--- /dev/null
+// 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.
+
+// Package bisect can be used by compilers and other programs
+// to serve as a target for the bisect debugging tool.
+// See [golang.org/x/tools/cmd/bisect] for details about using the tool.
+//
+// To be a bisect target, allowing bisect to help determine which of a set of independent
+// changes provokes a failure, a program needs to:
+//
+// 1. Define a way to accept a change pattern on its command line or in its environment.
+// The most common mechanism is a command-line flag.
+// The pattern can be passed to [New] to create a [Matcher], the compiled form of a pattern.
+//
+// 2. Assign each change a unique ID. One possibility is to use a sequence number,
+// but the most common mechanism is to hash some kind of identifying information
+// like the file and line number where the change might be applied.
+// [Hash] hashes its arguments to compute an ID.
+//
+// 3. Enable each change that the pattern says should be enabled.
+// The [Matcher.Enable] method answers this question for a given change ID.
+//
+// 4. Report each change that the pattern says should be reported.
+// The [Matcher.Report] method answers this question for a given change ID.
+// The report consists of one more lines on standard error or standard output
+// that contain a “match marker”. [Marker] returns the match marker for a given ID.
+// When bisect reports a change as causing the failure, it identifies the change
+// by printing those report lines, with the match marker removed.
+//
+// # Example Usage
+//
+// A program starts by defining how it receives the pattern. In this example, we will assume a flag.
+// The next step is to compile the pattern:
+//
+// m, err := bisect.New(patternFlag)
+// if err != nil {
+// log.Fatal(err)
+// }
+//
+// Then, each time a potential change is considered, the program computes
+// a change ID by hashing identifying information (source file and line, in this case)
+// and then calls m.ShouldEnable and m.ShouldReport to decide whether to
+// enable and report the change, respectively:
+//
+// for each change {
+// h := bisect.Hash(file, line)
+// if m.ShouldEnable(h) {
+// enableChange()
+// }
+// if m.ShouldReport(h) {
+// log.Printf("%v %s:%d", bisect.Marker(h), file, line)
+// }
+// }
+//
+// Note that the two return different values when bisect is searching for a
+// minimal set of changes to disable to provoke a failure.
+//
+// Finally, note that New returns a nil Matcher when there is no pattern,
+// meaning that the target is not running under bisect at all.
+// In that common case, the computation of the hash can be avoided entirely
+// by checking for m == nil first:
+//
+// for each change {
+// if m == nil {
+// enableChange()
+// } else {
+// h := bisect.Hash(file, line)
+// if m.ShouldEnable(h) {
+// enableChange()
+// }
+// if m.ShouldReport(h) {
+// log.Printf("%v %s:%d", bisect.Marker(h), file, line)
+// }
+// }
+// }
+//
+// # Pattern Syntax
+//
+// Patterns are generated by the bisect tool and interpreted by [New].
+// Users should not have to understand the patterns except when
+// debugging a target's bisect support or debugging the bisect tool itself.
+//
+// The pattern syntax selecting a change is a sequence of bit strings
+// separated by + and - operators. Each bit string denotes the set of
+// changes with IDs ending in those bits, + is set addition, - is set subtraction,
+// and the expression is evaluated in the usual left-to-right order.
+// The special binary number “y” denotes the set of all changes,
+// standing in for the empty bit string.
+// In the expression, all the + operators must appear before all the - operators.
+// A leading + adds to an empty set. A leading - subtracts from the set of all
+// possible suffixes.
+//
+// For example:
+//
+// - “01+10” and “+01+10” both denote the set of changes
+// with IDs ending with the bits 01 or 10.
+//
+// - “01+10-1001” denotes the set of changes with IDs
+// ending with the bits 01 or 10, but excluding those ending in 1001.
+//
+// - “-01-1000” and “y-01-1000 both denote the set of all changes
+// with IDs not ending in 01 nor 1000.
+//
+// - “0+1-01+001” is not a valid pattern, because all the + operators do not
+// appear before all the - operators.
+//
+// In the syntaxes described so far, the pattern specifies the changes to
+// enable and report. If a pattern is prefixed by a “!”, the meaning
+// changes: the pattern specifies the changes to DISABLE and report. This
+// mode of operation is needed when a program passes with all changes
+// enabled but fails with no changes enabled. In this case, bisect
+// searches for minimal sets of changes to disable.
+// Put another way, the leading “!” inverts the result from [Matcher.ShouldEnable]
+// but does not invert the result from [Matcher.ShouldReport].
+//
+// As a convenience for manual debugging, “n” is an alias for “!y”,
+// meaning to disable and report all changes.
+//
+// Finally, a leading “v” in the pattern indicates that the reports will be shown
+// to the user of bisect to describe the changes involved in a failure.
+// At the API level, the leading “v” causes [Matcher.Visible] to return true.
+// See the next section for details.
+//
+// # Match Reports
+//
+// The target program must enable only those changed matched
+// by the pattern, and it must print a match report for each such change.
+// A match report consists of one or more lines of text that will be
+// printed by the bisect tool to describe a change implicated in causing
+// a failure. Each line in the report for a given change must contain a
+// match marker with that change ID, as returned by [Marker].
+// The markers are elided when displaying the lines to the user.
+//
+// A match marker has the form “[bisect-match 0x1234]” where
+// 0x1234 is the change ID in hexadecimal.
+// An alternate form is “[bisect-match 010101]”, giving the change ID in binary.
+//
+// When [Matcher.Visible] returns false, the match reports are only
+// being processed by bisect to learn the set of enabled changes,
+// not shown to the user, meaning that each report can be a match
+// marker on a line by itself, eliding the usual textual description.
+// When the textual description is expensive to compute,
+// checking [Matcher.Visible] can help the avoid that expense
+// in most runs.
+package bisect
+
+// New creates and returns a new Matcher implementing the given pattern.
+// The pattern syntax is defined in the package doc comment.
+//
+// In addition to the pattern syntax syntax, New("") returns nil, nil.
+// The nil *Matcher is valid for use: it returns true from ShouldEnable
+// and false from ShouldReport for all changes. Callers can avoid calling
+// [Hash], [Matcher.ShouldEnable], and [Matcher.ShouldPrint] entirely
+// when they recognize the nil Matcher.
+func New(pattern string) (*Matcher, error) {
+ if pattern == "" {
+ return nil, nil
+ }
+
+ m := new(Matcher)
+
+ // Allow multiple v, so that “bisect cmd vPATTERN” can force verbose all the time.
+ p := pattern
+ for len(p) > 0 && p[0] == 'v' {
+ m.verbose = true
+ p = p[1:]
+ if p == "" {
+ return nil, &parseError{"invalid pattern syntax: " + pattern}
+ }
+ }
+
+ // Allow multiple !, each negating the last, so that “bisect cmd !PATTERN” works
+ // even when bisect chooses to add its own !.
+ m.enable = true
+ for len(p) > 0 && p[0] == '!' {
+ m.enable = !m.enable
+ p = p[1:]
+ if p == "" {
+ return nil, &parseError{"invalid pattern syntax: " + pattern}
+ }
+ }
+
+ if p == "n" {
+ // n is an alias for !y.
+ m.enable = !m.enable
+ p = "y"
+ }
+
+ // Parse actual pattern syntax.
+ result := true
+ bits := uint64(0)
+ start := 0
+ for i := 0; i <= len(p); i++ {
+ // Imagine a trailing - at the end of the pattern to flush final suffix
+ c := byte('-')
+ if i < len(p) {
+ c = p[i]
+ }
+ switch c {
+ default:
+ return nil, &parseError{"invalid pattern syntax: " + pattern}
+ case '0', '1':
+ bits = bits<<1 | uint64(c-'0')
+ case 'y':
+ if i+1 < len(p) && (p[i+1] == '0' || p[i+1] == '1') {
+ return nil, &parseError{"invalid pattern syntax: " + pattern}
+ }
+ bits = 0
+ case '+', '-':
+ if c == '+' && result == false {
+ // Have already seen a -. Should be - from here on.
+ return nil, &parseError{"invalid pattern syntax (+ after -): " + pattern}
+ }
+ if i > 0 {
+ n := i - start
+ if n > 64 {
+ return nil, &parseError{"pattern bits too long: " + pattern}
+ }
+ if n <= 0 {
+ return nil, &parseError{"invalid pattern syntax: " + pattern}
+ }
+ if p[start] == 'y' {
+ n = 0
+ }
+ mask := uint64(1)<<n - 1
+ m.list = append(m.list, cond{mask, bits, result})
+ } else if c == '-' {
+ // leading - subtracts from complete set
+ m.list = append(m.list, cond{0, 0, true})
+ }
+ bits = 0
+ result = c == '+'
+ start = i + 1
+ }
+ }
+ return m, nil
+}
+
+// A Matcher is the parsed, compiled form of a PATTERN string.
+// The nil *Matcher is valid: it has all changes enabled but none reported.
+type Matcher struct {
+ verbose bool
+ enable bool // when true, list is for “enable and report” (when false, “disable and report”)
+ list []cond // conditions; later ones win over earlier ones
+}
+
+// A cond is a single condition in the matcher.
+// Given an input id, if id&mask == bits, return the result.
+type cond struct {
+ mask uint64
+ bits uint64
+ result bool
+}
+
+// Verbose reports whether the reports will be shown to users
+// and need to include a human-readable change description.
+// If not, the target can print just the Marker on a line by itself
+// and perhaps save some computation.
+func (m *Matcher) Verbose() bool {
+ return m.verbose
+}
+
+// ShouldEnable reports whether the change with the given id should be enabled.
+func (m *Matcher) ShouldEnable(id uint64) bool {
+ if m == nil {
+ return true
+ }
+ for i := len(m.list) - 1; i >= 0; i-- {
+ c := &m.list[i]
+ if id&c.mask == c.bits {
+ return c.result == m.enable
+ }
+ }
+ return false == m.enable
+}
+
+// ShouldReport reports whether the change with the given id should be reported.
+func (m *Matcher) ShouldReport(id uint64) bool {
+ if m == nil {
+ return false
+ }
+ for i := len(m.list) - 1; i >= 0; i-- {
+ c := &m.list[i]
+ if id&c.mask == c.bits {
+ return c.result
+ }
+ }
+ return false
+}
+
+// Marker returns the match marker text to use on any line reporting details
+// about a match of the given ID.
+// It always returns the hexadecimal format.
+func Marker(id uint64) string {
+ return string(AppendMarker(nil, id))
+}
+
+// AppendMarker is like [Marker] but appends the marker to dst.
+func AppendMarker(dst []byte, id uint64) []byte {
+ const prefix = "[bisect-match 0x"
+ var buf [len(prefix) + 16 + 1]byte
+ copy(buf[:], prefix)
+ for i := 0; i < 16; i++ {
+ buf[len(prefix)+i] = "0123456789abcdef"[id>>60]
+ id <<= 4
+ }
+ buf[len(prefix)+16] = ']'
+ return append(dst, buf[:]...)
+}
+
+// CutMarker finds the first match marker in line and removes it,
+// returning the shortened line (with the marker removed),
+// the ID from the match marker,
+// and whether a marker was found at all.
+// If there is no marker, CutMarker returns line, 0, false.
+func CutMarker(line string) (short string, id uint64, ok bool) {
+ // Find first instance of prefix.
+ prefix := "[bisect-match "
+ i := 0
+ for ; ; i++ {
+ if i >= len(line)-len(prefix) {
+ return line, 0, false
+ }
+ if line[i] == '[' && line[i:i+len(prefix)] == prefix {
+ break
+ }
+ }
+
+ // Scan to ].
+ j := i + len(prefix)
+ for j < len(line) && line[j] != ']' {
+ j++
+ }
+ if j >= len(line) {
+ return line, 0, false
+ }
+
+ // Parse id.
+ idstr := line[i+len(prefix) : j]
+ if len(idstr) >= 3 && idstr[:2] == "0x" {
+ // parse hex
+ if len(idstr) > 2+16 { // max 0x + 16 digits
+ return line, 0, false
+ }
+ for i := 2; i < len(idstr); i++ {
+ id <<= 4
+ switch c := idstr[i]; {
+ case '0' <= c && c <= '9':
+ id |= uint64(c - '0')
+ case 'a' <= c && c <= 'f':
+ id |= uint64(c - 'a' + 10)
+ case 'A' <= c && c <= 'F':
+ id |= uint64(c - 'A' + 10)
+ }
+ }
+ } else {
+ if idstr == "" || len(idstr) > 64 { // min 1 digit, max 64 digits
+ return line, 0, false
+ }
+ // parse binary
+ for i := 0; i < len(idstr); i++ {
+ id <<= 1
+ switch c := idstr[i]; c {
+ default:
+ return line, 0, false
+ case '0', '1':
+ id |= uint64(c - '0')
+ }
+ }
+ }
+
+ // Construct shortened line.
+ // Remove at most one space from around the marker,
+ // so that "foo [marker] bar" shortens to "foo bar".
+ j++ // skip ]
+ if i > 0 && line[i-1] == ' ' {
+ i--
+ } else if j < len(line) && line[j] == ' ' {
+ j++
+ }
+ short = line[:i] + line[j:]
+ return short, id, true
+}
+
+// Hash computes a hash of the data arguments,
+// each of which must be of type string, byte, int, uint, int32, uint32, int64, uint64, uintptr, or a slice of one of those types.
+func Hash(data ...any) uint64 {
+ h := offset64
+ for _, v := range data {
+ switch v := v.(type) {
+ default:
+ // Note: Not printing the type, because reflect.ValueOf(v)
+ // would make the interfaces prepared by the caller escape
+ // and therefore allocate. This way, Hash(file, line) runs
+ // without any allocation. It should be clear from the
+ // source code calling Hash what the bad argument was.
+ panic("bisect.Hash: unexpected argument type")
+ case string:
+ h = fnvString(h, v)
+ case byte:
+ h = fnv(h, v)
+ case int:
+ h = fnvUint64(h, uint64(v))
+ case uint:
+ h = fnvUint64(h, uint64(v))
+ case int32:
+ h = fnvUint32(h, uint32(v))
+ case uint32:
+ h = fnvUint32(h, v)
+ case int64:
+ h = fnvUint64(h, uint64(v))
+ case uint64:
+ h = fnvUint64(h, v)
+ case uintptr:
+ h = fnvUint64(h, uint64(v))
+ case []string:
+ for _, x := range v {
+ h = fnvString(h, x)
+ }
+ case []byte:
+ for _, x := range v {
+ h = fnv(h, x)
+ }
+ case []int:
+ for _, x := range v {
+ h = fnvUint64(h, uint64(x))
+ }
+ case []uint:
+ for _, x := range v {
+ h = fnvUint64(h, uint64(x))
+ }
+ case []int32:
+ for _, x := range v {
+ h = fnvUint32(h, uint32(x))
+ }
+ case []uint32:
+ for _, x := range v {
+ h = fnvUint32(h, x)
+ }
+ case []int64:
+ for _, x := range v {
+ h = fnvUint64(h, uint64(x))
+ }
+ case []uint64:
+ for _, x := range v {
+ h = fnvUint64(h, x)
+ }
+ case []uintptr:
+ for _, x := range v {
+ h = fnvUint64(h, uint64(x))
+ }
+ }
+ }
+ return h
+}
+
+// Trivial error implementation, here to avoid importing errors.
+
+type parseError struct{ text string }
+
+func (e *parseError) Error() string { return e.text }
+
+// FNV-1a implementation. See Go's hash/fnv/fnv.go.
+// Copied here for simplicity (can handle uints directly)
+// and to avoid the dependency.
+
+const (
+ offset64 uint64 = 14695981039346656037
+ prime64 uint64 = 1099511628211
+)
+
+func fnv(h uint64, x byte) uint64 {
+ h ^= uint64(x)
+ h *= prime64
+ return h
+}
+
+func fnvString(h uint64, x string) uint64 {
+ for i := 0; i < len(x); i++ {
+ h ^= uint64(x[i])
+ h *= prime64
+ }
+ return h
+}
+
+func fnvUint64(h uint64, x uint64) uint64 {
+ for i := 0; i < 8; i++ {
+ h ^= uint64(x & 0xFF)
+ x >>= 8
+ h *= prime64
+ }
+ return h
+}
+
+func fnvUint32(h uint64, x uint32) uint64 {
+ for i := 0; i < 4; i++ {
+ h ^= uint64(x & 0xFF)
+ x >>= 8
+ h *= prime64
+ }
+ return h
+}