From 5a59a01dc67331dfde3f7753a3ca90c0755eb211 Mon Sep 17 00:00:00 2001
From: Charlie Yang <charlie.yang@salesforce.com>
Date: Wed, 14 Sep 2016 23:48:16 -0700
Subject: Return a sensible error on unknown file type

Provide a more detailed error message when the image file type cannot
be determined via magic or extension. Previously the error message said

    attempt to concatenate local 'ext' (a nil value)
---
 assets/bmp-without-ext | Bin 0 -> 142 bytes
 init.lua               |   2 ++
 test/test.lua          |  11 +++++++++++
 3 files changed, 13 insertions(+)
 create mode 100644 assets/bmp-without-ext

diff --git a/assets/bmp-without-ext b/assets/bmp-without-ext
new file mode 100644
index 0000000..0d7f4eb
Binary files /dev/null and b/assets/bmp-without-ext differ
diff --git a/init.lua b/init.lua
index 619d9b7..4d9350e 100644
--- a/init.lua
+++ b/init.lua
@@ -366,6 +366,8 @@ local function load(filename, depth, tensortype)
    local tensor
    if image.is_supported(ext) then
       tensor = filetypes[ext].loader(filename, depth, tensortype)
+   elseif not ext then
+      dok.error('unable to determine image type for file: ' .. filename, 'image.load')
    else
       dok.error('unknown image type: ' .. ext, 'image.load')
    end
diff --git a/test/test.lua b/test/test.lua
index 80299e9..0a25cd9 100644
--- a/test/test.lua
+++ b/test/test.lua
@@ -634,6 +634,17 @@ function test.test_pbmload()
   )
 end
 
+----------------------------------------------------------------------
+-- Load unknown image type without extension test
+--
+function test.LoadUnknownImageTypeWithoutExtension()
+  tester:assertErrorPattern(
+    function() image.load(getTestImagePath("bmp-without-ext")) end,
+    "unable to determine image type for file",
+    "unknown image type should not be loaded or unexpected error message"
+  )
+end
+
 ----------------------------------------------------------------------
 -- Text drawing test
 --
-- 
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