From 21eee45a488e70686d09f2d2926bd048901a867e Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Sun, 16 Jan 2011 19:01:45 -0700
Subject: [PATCH] fix `read-language' when input has only comments

---
 collects/scribblings/reference/read.scrbl |  2 +-
 collects/tests/racket/read.rktl           | 18 ++++++++++++++++++
 src/racket/src/read.c                     |  2 ++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/collects/scribblings/reference/read.scrbl b/collects/scribblings/reference/read.scrbl
index 3e970e33bf..9355611abb 100644
--- a/collects/scribblings/reference/read.scrbl
+++ b/collects/scribblings/reference/read.scrbl
@@ -163,7 +163,7 @@ exception is propagated by @racket[read-language].
 If @racket[in] does not specify a @tech{reader language} with
 @litchar{#lang} or @litchar{#!}, then @racket[fail-thunk] is
 called. The default @racket[fail-thunk] raises
-@racket[exn:fail:contract].}
+@racket[exn:fail:read] or @racket[exn:fail:read:eof].}
 
 
 @defboolparam[read-case-sensitive on?]{
diff --git a/collects/tests/racket/read.rktl b/collects/tests/racket/read.rktl
index eae885b61f..55a860963a 100644
--- a/collects/tests/racket/read.rktl
+++ b/collects/tests/racket/read.rktl
@@ -1078,6 +1078,24 @@
                (and (exn:fail:read? x)
                     (not (exn:fail:read:eof? x)))))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; read-language
+
+(test #t procedure? (read-language (open-input-string "#lang racket/base")))
+(test #t procedure? (read-language (open-input-string ";;\n#lang racket/base")))
+(test #t procedure? (read-language (open-input-string ";;\n#|\n\n   |#\n#lang racket/base")))
+(test #t procedure? (read-language (open-input-string "#! /bin/env \n#lang racket/base")))
+(test #t procedure? (read-language (open-input-string "#!/bin/env \n#lang racket/base")))
+(test #t procedure? (read-language (open-input-string "#!racket/base")))
+(let ([check-nothing
+       (lambda (str exn?)
+         (err/rt-test (read-language (open-input-string str)) exn?)
+         (test 'no read-language (open-input-string str) (lambda () 'no)))])
+  (check-nothing "" exn:fail:read:eof?)
+  (check-nothing ";" exn:fail:read:eof?)
+  (check-nothing "#| |#" exn:fail:read:eof?)
+  (check-nothing "8 9" exn:fail:read?))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)
diff --git a/src/racket/src/read.c b/src/racket/src/read.c
index b4a252b426..a1e31523d0 100644
--- a/src/racket/src/read.c
+++ b/src/racket/src/read.c
@@ -1088,6 +1088,8 @@ read_inner_inner(Scheme_Object *port, Scheme_Object *stxsrc, Scheme_Hash_Table *
 	  if (ch == EOF) {
             if (comment_mode & RETURN_FOR_COMMENT)
               return NULL;
+            if (get_info)
+              return expected_lang("", ch, port, stxsrc, line, col, pos, get_info);
 	    return scheme_eof;
           }
 	  if (ch == SCHEME_SPECIAL)