pkg/repro: fix invalid options minimization

Repro can generate Sandbox="namespace"/UseTmpDir=false.
This combination is broken for two reasons:
 - on second and subsequent executions of the program,
   it fails to create syz-tmp dir
 - with Procs>1, it fails right away, because all procs
   try to create syz-tmp dir

Don't generate such combination.

pkg/csource/csource.go

@@ -51,11 +51,19 @@ type Options struct {
 // Invalid combinations must not be passed to Write.
 func (opts Options) Check() error {
 	if !opts.Threaded && opts.Collide {
+		// Collide requires threaded.
 		return errors.New("Collide without Threaded")
 	}
 	if !opts.Repeat && opts.Procs > 1 {
+		// This does not affect generated code.
 		return errors.New("Procs>1 without Repeat")
 	}
+	if opts.Sandbox == "namespace" && !opts.UseTmpDir {
+		// This is borken and never worked.
+		// This tries to create syz-tmp dir in cwd,
+		// which will fail if procs>1 and on second run of the program.
+		return errors.New("Sandbox=namespace without UseTmpDir")
+	}
 	return nil
 }
 

pkg/csource/csource_test.go

@@ -85,12 +85,13 @@ func allOptionsPermutations() []Options {
 func TestOne(t *testing.T) {
 	rs, _ := initTest(t)
 	opts := Options{
-		Threaded: true,
-		Collide:  true,
-		Repeat:   true,
-		Procs:    2,
-		Sandbox:  "namespace",
-		Repro:    true,
+		Threaded:  true,
+		Collide:   true,
+		Repeat:    true,
+		Procs:     2,
+		Sandbox:   "namespace",
+		Repro:     true,
+		UseTmpDir: true,
 	}
 	p := prog.GenerateAllSyzProg(rs)
 	testOne(t, p, opts)

pkg/repro/repro.go

@@ -792,7 +792,7 @@ var cSimplifies = append(progSimplifies, []Simplify{
 		return true
 	},
 	func(opts *csource.Options) bool {
-		if !opts.UseTmpDir {
+		if !opts.UseTmpDir || opts.Sandbox == "namespace" {
 			return false
 		}
 		opts.UseTmpDir = false

pkg/repro/repro_test.go

@@ -78,13 +78,18 @@ func TestSimplifies(t *testing.T) {
 		WaitRepeat: true,
 		Repro:      true,
 	}
-	if err := opts.Check(); err != nil {
-		t.Fatalf("initial opts are invalid: %v", err)
-	}
-	for i, fn := range cSimplifies {
-		fn(&opts)
+	var check func(opts csource.Options, i int)
+	check = func(opts csource.Options, i int) {
 		if err := opts.Check(); err != nil {
-			t.Fatalf("opts %v are invalid: %v", i, err)
+			t.Fatalf("opts are invalid: %v", err)
+		}
+		if i == len(cSimplifies) {
+			return
+		}
+		check(opts, i+1)
+		if cSimplifies[i](&opts) {
+			check(opts, i+1)
 		}
 	}
+	check(opts, 0)
 }