gears.filesystem: Improve get_random_file_from_dir.

Previously, only a filename was returned. Getting the path was
inconvinient when used within a declarative construct.

It was also misbehaving then the directory didn't exist. Finally,
the extention list now accept extension names starting with a dot.

lib/gears/filesystem.lua

@@ -172,28 +172,39 @@ end
 -- @tparam string path The directory to search.
 -- @tparam[opt] table exts Specific extensions to limit the search to. eg:`{ "jpg", "png" }`
 --   If ommited, all files are considered.
+-- @tparam[opt=false] boolean absolute_path Return the absolute path instead of the filename.
 -- @treturn string|nil A randomly selected filename from the specified path (with
---   a specified extension if required) or nil if no suitable file is found.
+--   a specified extension if required) or nil if no suitable file is found. If `absolute_path`
+--   is set, then a path is returned instead of a file name.
 -- @staticfct gears.filesystem.get_random_file_from_dir
-function filesystem.get_random_file_from_dir(path, exts)
+function filesystem.get_random_file_from_dir(path, exts, absolute_path)
     local files, valid_exts = {}, {}
 
     -- Transforms { "jpg", ... } into { [jpg] = #, ... }
-    if exts then for i, j in ipairs(exts) do valid_exts[j:lower()] = i end end
+    if exts then for i, j in ipairs(exts) do valid_exts[j:lower():gsub("^[.]", "")] = i end end
 
     -- Build a table of files from the path with the required extensions
     local file_list = Gio.File.new_for_path(path):enumerate_children("standard::*", 0)
+
+    -- This will happen when the directory doesn't exist.
+    if not file_list then return nil end
+
     for file in function() return file_list:next_file() end do
         if file:get_file_type() == "REGULAR" then
             local file_name = file:get_display_name()
+
             if not exts or valid_exts[file_name:lower():match(".+%.(.*)$") or ""] then
                table.insert(files, file_name)
             end
         end
     end
 
+    if #files == 0 then return nil end
+
     -- Return a randomly selected filename from the file table
-    return #files > 0 and files[math.random(#files)] or nil
+    local file = files[math.random(#files)]
+
+    return absolute_path and (path:gsub("[/]*$", "") .. "/" .. file) or file
 end
 
 return filesystem

spec/gears/filesystem_spec.lua

@@ -115,22 +115,40 @@ describe("gears.filesystem", function()
             assert.is_true(test_b == "a.png"
                         or test_b == "b.jpg")
 
+            -- Any file found (selected extensions)
+            local test_c = gfs.get_random_file_from_dir(root .. "filesystem_tests", {".png", ".jpg"})
+            assert.is_true(test_c == "a.png"
+                        or test_c == "b.jpg")
+
+            -- Test absolute paths.
+            local test_d = gfs.get_random_file_from_dir(root .. "filesystem_tests", {".png", ".jpg"}, true)
+            assert.is_true(test_d == root .. "filesystem_tests/a.png"
+                        or test_d == root .. "filesystem_tests/b.jpg")
+
+            -- Make sure the paths are generated correctly.
+            assert.is_nil(test_d:match("//"))
+
             -- "." in filename test cases with extensions
-            local test_c = gfs.get_random_file_from_dir(root .. "filesystem_tests/y", {"ext"})
-            assert.is_true(test_c == "filename.ext"
-                         or test_c == ".filename.ext"
-                        or test_c == "file.name.ext"
-                        or test_c == ".file.name.ext")
+            local test_e = gfs.get_random_file_from_dir(root .. "filesystem_tests/y", {"ext"})
+            assert.is_true(test_e == "filename.ext"
+                         or test_e == ".filename.ext"
+                        or test_e == "file.name.ext"
+                        or test_e == ".file.name.ext")
 
             -- "." in filename test cases with no extensions
-            local test_d = gfs.get_random_file_from_dir(root .. "filesystem_tests/y", {""})
-            assert.is_true(test_d == "filename"
-                        or test_d == "filename."
-                        or test_d == "filename.ext."
-                        or test_d == ".filename"
-                        or test_d == ".filename."
-                        or test_d == "file.name.ext."
-                        or test_d == ".file.name.ext.")
+            local test_f = gfs.get_random_file_from_dir(root .. "filesystem_tests/y", {""})
+            assert.is_true(test_f == "filename"
+                        or test_f == "filename."
+                        or test_f == "filename.ext."
+                        or test_f == ".filename"
+                        or test_f == ".filename."
+                        or test_f == "file.name.ext."
+                        or test_f == ".file.name.ext.")
+
+            -- Test invalid directories.
+            local test_g = gfs.get_random_file_from_dir(root .. "filesystem_tests/fake_dir")
+            assert.is_nil(test_g)
+
         end
     end)
 end)