go/ast, go/parser: correct End() position for *ast.EmptyStmt

- added a new field ast.EmptyStmt.Implicit to indicate explicit
  or implicit semicolon
- fix ast.EmptyStmt.End() accordingly
- adjusted parser and added test case

Fixes #9979.

Change-Id: I72b0983b3a0cabea085598e1bf6c8df629776b57
Reviewed-on: https://go-review.googlesource.com/5720
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
index 0409122c81..d1b766cfbb 100644
--- a/src/go/parser/parser.go
+++ b/src/go/parser/parser.go
@@ -2152,11 +2152,14 @@ func (p *parser) parseStmt() (s ast.Stmt) {
 	case token.FOR:
 		s = p.parseForStmt()
 	case token.SEMICOLON:
-		s = &ast.EmptyStmt{Semicolon: p.pos}
+		// Is it ever possible to have an implicit semicolon
+		// producing an empty statement in a valid program?
+		// (handle correctly anyway)
+		s = &ast.EmptyStmt{Semicolon: p.pos, Implicit: p.lit == "\n"}
 		p.next()
 	case token.RBRACE:
 		// a semicolon may be omitted before a closing "}"
-		s = &ast.EmptyStmt{Semicolon: p.pos}
+		s = &ast.EmptyStmt{Semicolon: p.pos, Implicit: true}
 	default:
 		// no statement found
 		pos := p.pos