From d52c84545425d4436d3bfb47743c2c3a2dd4aa7b Mon Sep 17 00:00:00 2001
From: Ben Greenman <benjaminlgreenman@gmail.com>
Date: Mon, 24 Feb 2020 20:49:58 -0500
Subject: [PATCH] racket/file: check file-exists?

Check `file-exists?` before passing the file on to `file-size` and/or
`open-input-file`. The latter led to confusing error messages, e.g.:

```
(file->string "DNE")
;; file-size: cannot get size
```

affects: `file->value` `file->list` `file->string` `file->bytes`
 `file->lines` `file->bytes-lines`
---
 pkgs/racket-test-core/tests/racket/filelib.rktl | 11 +++++++++++
 racket/collects/racket/file.rkt                 | 14 ++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/pkgs/racket-test-core/tests/racket/filelib.rktl b/pkgs/racket-test-core/tests/racket/filelib.rktl
index aa289a4a63..9bfbf97c0f 100644
--- a/pkgs/racket-test-core/tests/racket/filelib.rktl
+++ b/pkgs/racket-test-core/tests/racket/filelib.rktl
@@ -29,6 +29,17 @@
 (test #"\"\316\273\"" file->bytes tmp-name)
 (test "\u03BB" file->value tmp-name)
 (when (file-exists? tmp-name) (delete-file tmp-name))
+(define-syntax-rule (err/rt-exists-test (op arg ...))
+  (err/rt-test (op arg ...) (check-exists 'op)))
+(define (check-exists op)
+  (lambda (exn)
+    (regexp-match? (format "^~a: .* file-exists\\?" op) (exn-message exn))))
+(err/rt-exists-test (file->value tmp-name))
+(err/rt-exists-test (file->list tmp-name))
+(err/rt-exists-test (file->string tmp-name))
+(err/rt-exists-test (file->bytes tmp-name))
+(err/rt-exists-test (file->lines tmp-name))
+(err/rt-exists-test (file->bytes-lines tmp-name))
 (delete-directory tmp-dir)
 
 (define-syntax-rule (err/rt-chk-test (op arg ...))
diff --git a/racket/collects/racket/file.rkt b/racket/collects/racket/file.rkt
index 64a28f6458..3ae352ba09 100644
--- a/racket/collects/racket/file.rkt
+++ b/racket/collects/racket/file.rkt
@@ -752,16 +752,18 @@
                           new (cons base new)))
             (loop (cdr paths) (append (reverse new) r))))))))
 
-(define (check-path who f)
+(define (check-path-exists who f)
   (unless (path-string? f)
-    (raise-argument-error who "path-string?" f)))
+    (raise-argument-error who "path-string?" f))
+  (unless (file-exists? f)
+    (raise-argument-error who "file-exists?" f)))
 
 (define (check-file-mode who file-mode)
   (unless (memq file-mode '(binary text))
     (raise-argument-error who "(or/c 'binary 'text)" file-mode)))
 
 (define (file->x who f file-mode read-x x-append)
-  (check-path who f)
+  (check-path-exists who f)
   (check-file-mode who file-mode)
   (let ([sz (file-size f)])
     (call-with-input-file* f #:mode file-mode
@@ -781,12 +783,12 @@
   (file->x 'file->bytes f mode read-bytes bytes-append))
 
 (define (file->value f #:mode [file-mode 'binary])
-  (check-path 'file->value f)
+  (check-path-exists 'file->value f)
   (check-file-mode 'file->value file-mode)
   (call-with-input-file* f #:mode file-mode read))
 
 (define (file->list f [r read] #:mode [file-mode 'binary])
-  (check-path 'file->list f)
+  (check-path-exists 'file->list f)
   (check-file-mode 'file->list file-mode)
   (unless (and (procedure? r) (procedure-arity-includes? r 1))
     (raise-argument-error 'file->list "(procedure-arity-includes/c 1)" r))
@@ -794,7 +796,7 @@
     (lambda (p) (for/list ([v (in-port r p)]) v))))
 
 (define (file->x-lines who f line-mode file-mode read-line)
-  (check-path who f)
+  (check-path-exists who f)
   (check-mode who line-mode)
   (check-file-mode who file-mode)
   (call-with-input-file* f #:mode file-mode