go.tools/go/types, cmd/gotype: fix early bailout

Clients must have chance to look at panics they
are raising.

R=adonovan
CC=golang-dev
https://golang.org/cl/23820043

cmd/gotype/gotype.go

@@ -196,10 +196,12 @@ func checkPkgFiles(files []*ast.File) {
 	}
 
 	defer func() {
-		switch err := recover().(type) {
+		switch p := recover().(type) {
 		case nil, bailout:
+			// normal return or early exit
 		default:
-			panic(err)
+			// re-panic
+			panic(p)
 		}
 	}()
 

go/types/check.go

@@ -7,7 +7,6 @@
 package types
 
 import (
-	"fmt"
 	"go/ast"
 	"go/token"
 	"path"
@@ -173,15 +172,10 @@ func (check *checker) handleBailout(err *error) {
 		// normal return or early exit
 		*err = check.firstErr
 	default:
-		// unexpected panic: don't crash clients
-		// TODO(gri) add a test case for this scenario
-		*err = fmt.Errorf("types internal error: %v", p)
-		if debug {
-			check.dump("INTERNAL PANIC: %v", p)
+		// re-panic
 		panic(p)
 	}
 }
-}
 
 func (conf *Config) check(pkgPath string, fset *token.FileSet, files []*ast.File, info *Info) (pkg *Package, err error) {
 	// make sure we have a package canonicalization map