[dev.fuzz] internal/fuzz: read and write interesting values in fuzz cache

'go test -fuzz' may now read and write interesting fuzzing values to
directories in $GOCACHE/fuzz. Files in this directory are named
$pkg/$test/$hash where $pkg is the package path containing the fuzz
target, $test is the target name, and $hash is the SHA-256 sum of the
data in the file.

Note that different versions of the same package or packages with the
same path from different modules may share the same directory.

Although files are written into a subdirectory of GOCACHE, they are
not removed automatically, nor are they removed by 'go clean -cache'.
Instead, they may be removed with 'go clean -fuzzcache'. We chose to
nest the fuzzing directory inside GOCACHE to avoid introducing a new
environment variable, since there's no real need for users to specify
a separate directory.

Change-Id: I2032cf8e6c92f715cf36a9fc6a550acf666d2382
Reviewed-on: https://go-review.googlesource.com/c/go/+/275534
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
Trust: Katie Hockman <katie@golang.org>
Trust: Jay Conrod <jayconrod@google.com>

1 files changed, 18 insertions, 12 deletions

diff --git a/src/testing/testing.go b/src/testing/testing.go
index c87e0a5b9a..e3e35fa13a 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -1353,17 +1353,17 @@ var errMain = errors.New("testing: unexpected use of func Main")
 
 type matchStringOnly func(pat, str string) (bool, error)
 
-func (f matchStringOnly) MatchString(pat, str string) (bool, error)     { return f(pat, str) }
-func (f matchStringOnly) StartCPUProfile(w io.Writer) error             { return errMain }
-func (f matchStringOnly) StopCPUProfile()                               {}
-func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error   { return errMain }
-func (f matchStringOnly) ImportPath() string                            { return "" }
-func (f matchStringOnly) StartTestLog(io.Writer)                        {}
-func (f matchStringOnly) StopTestLog() error                            { return errMain }
-func (f matchStringOnly) SetPanicOnExit0(bool)                          {}
-func (f matchStringOnly) CoordinateFuzzing(int, [][]byte, string) error { return errMain }
-func (f matchStringOnly) RunFuzzWorker(func([]byte) error) error        { return errMain }
-func (f matchStringOnly) ReadCorpus(string) ([][]byte, error)           { return nil, errMain }
+func (f matchStringOnly) MatchString(pat, str string) (bool, error)             { return f(pat, str) }
+func (f matchStringOnly) StartCPUProfile(w io.Writer) error                     { return errMain }
+func (f matchStringOnly) StopCPUProfile()                                       {}
+func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error           { return errMain }
+func (f matchStringOnly) ImportPath() string                                    { return "" }
+func (f matchStringOnly) StartTestLog(io.Writer)                                {}
+func (f matchStringOnly) StopTestLog() error                                    { return errMain }
+func (f matchStringOnly) SetPanicOnExit0(bool)                                  {}
+func (f matchStringOnly) CoordinateFuzzing(int, [][]byte, string, string) error { return errMain }
+func (f matchStringOnly) RunFuzzWorker(func([]byte) error) error                { return errMain }
+func (f matchStringOnly) ReadCorpus(string) ([][]byte, error)                   { return nil, errMain }
 
 // Main is an internal function, part of the implementation of the "go test" command.
 // It was exported because it is cross-package and predates "internal" packages.
@@ -1406,7 +1406,7 @@ type testDeps interface {
 	StartTestLog(io.Writer)
 	StopTestLog() error
 	WriteProfileTo(string, io.Writer, int) error
-	CoordinateFuzzing(int, [][]byte, string) error
+	CoordinateFuzzing(int, [][]byte, string, string) error
 	RunFuzzWorker(func([]byte) error) error
 	ReadCorpus(string) ([][]byte, error)
 }
@@ -1448,6 +1448,12 @@ func (m *M) Run() (code int) {
 		m.exitCode = 2
 		return
 	}
+	if *matchFuzz != "" && *fuzzCacheDir == "" {
+		fmt.Fprintln(os.Stderr, "testing: internal error: -test.fuzzcachedir must be set if -test.fuzz is set")
+		flag.Usage()
+		m.exitCode = 2
+		return
+	}
 
 	if len(*matchList) != 0 {
 		listTests(m.deps.MatchString, m.tests, m.benchmarks, m.fuzzTargets, m.examples)