Handle File.extname edge case (#6234)

* Fix #6215. Handle File.extname edge case * Fix typo * Use byte_slice * Remove local variable * On less return in the world * Iterate bytes * Empty case
crystal-lang · Jun 25, 2018 · 9d99700 · 9d99700
1 parent 9228889
commit 9d99700
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diff --git a/spec/std/file_spec.cr b/spec/std/file_spec.cr
@@ -297,18 +297,22 @@ describe "File" do
   end
 
   it "gets extname" do
+    File.extname("/foo/bar/a.cr").should eq(".cr")
     File.extname("/foo/bar/baz.cr").should eq(".cr")
     File.extname("/foo/bar/baz.cr.cz").should eq(".cz")
     File.extname("/foo/bar/.profile").should eq("")
     File.extname("/foo/bar/.profile.sh").should eq(".sh")
     File.extname("/foo/bar/foo.").should eq("")
     File.extname("/foo.bar/baz").should eq("")
+    File.extname("a.cr").should eq(".cr")
     File.extname("test.cr").should eq(".cr")
     File.extname("test.cr.cz").should eq(".cz")
     File.extname(".test").should eq("")
     File.extname(".test.cr").should eq(".cr")
     File.extname(".test.cr.cz").should eq(".cz")
     File.extname("test").should eq("")
+    File.extname("test.").should eq("")
+    File.extname("").should eq("")
   end
 
   it "constructs a path from parts" do

diff --git a/src/file.cr b/src/file.cr
@@ -282,13 +282,40 @@ class File < IO::FileDescriptor
   def self.extname(filename) : String
     filename.check_no_null_byte
 
-    dot_index = filename.rindex('.')
+    bytes = filename.to_slice
 
-    if dot_index && dot_index != filename.size - 1 && dot_index - 1 > (filename.rindex(SEPARATOR) || 0)
-      filename[dot_index, filename.size - dot_index]
-    else
-      ""
+    return "" if bytes.empty?
+
+    current = bytes.size - 1
+
+    # if the pattern is foo. it has no extension
+    return "" if bytes[current] == '.'.ord
+
+    # position the reader at the last . or SEPARATOR
+    # that is not the first char
+    while bytes[current] != SEPARATOR.ord &&
+          bytes[current] != '.'.ord &&
+          current > 0
+      current -= 1
     end
+
+    # if we are the beginning of the string there is no extension
+    # /foo or .foo have no extension
+    return "" unless current > 0
+
+    # otherwise we are not at the beginning, and there is a previous char.
+    # if current is '/', then the pattern is prefix/foo and has no extension
+    return "" if bytes[current] == SEPARATOR.ord
+
+    # otherwise the current_char is '.'
+    # if previous is '/', then the pattern is prefix/.foo  and has no extension
+    return "" if bytes[current - 1] == SEPARATOR.ord
+
+    # So the current char is '.',
+    # we are not at the beginning,
+    # the previous char is not a '/',
+    # and we have an extension
+    String.new(bytes[current, bytes.size - current])
   end
 
   # Converts *path* to an absolute path. Relative paths are