cmd/internal/objabi: add support for bisect.Matcher debug flags

Makes it more convenient to add new bisection targets.

Change-Id: I7ac14018bac1e25751234a2267f8747a281b6088
Reviewed-on: https://go-review.googlesource.com/c/go/+/517616
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>
Reviewed-by: David Chase <[email protected]>

src/cmd/internal/objabi/flag.go

@@ -7,6 +7,7 @@ package objabi
 import (
 	"flag"
 	"fmt"
+	"internal/bisect"
 	"internal/buildcfg"
 	"io"
 	"log"
@@ -262,8 +263,8 @@ func NewDebugFlag(debug interface{}, debugSSA DebugSSA) *DebugFlag {
 
 		switch ptr.(type) {
 		default:
-			panic(fmt.Sprintf("debug.%s has invalid type %v (must be int or string)", f.Name, f.Type))
-		case *int, *string:
+			panic(fmt.Sprintf("debug.%s has invalid type %v (must be int, string, or *bisect.Matcher)", f.Name, f.Type))
+		case *int, *string, **bisect.Matcher:
 			// ok
 		}
 		flag.tab[name] = debugField{name, help, concurrent == "ok", ptr}
@@ -328,6 +329,12 @@ func (f *DebugFlag) Set(debugstr string) error {
 					log.Fatalf("invalid debug value %v", name)
 				}
 				*vp = val
+			case **bisect.Matcher:
+				var err error
+				*vp, err = bisect.New(valstring)
+				if err != nil {
+					log.Fatalf("debug flag %v: %v", name, err)
+				}
 			default:
 				panic("bad debugtab type")
 			}