[fix] DocumentRegistry: don't create empty sdr and add hasProvider() (#3675)

As suggested by @poire-z https://github.com/koreader/koreader/pull/3653#issuecomment-364663156

frontend/apps/cloudstorage/dropboxapi.lua

@@ -104,14 +104,14 @@ function DropBoxApi:listFolder(path, token)
             table.insert(dropbox_list, {
                 text = text,
                 url = files.path_display,
-                type = tag
+                type = tag,
             })
         --show only file with supported formats
-        elseif tag == "file" and DocumentRegistry:getProvider(text) then
+        elseif tag == "file" and DocumentRegistry:hasProvider(text) then
             table.insert(dropbox_file, {
                 text = text,
                 url = files.path_display,
-                type = tag
+                type = tag,
             })
         end
     end
@@ -126,7 +126,7 @@ function DropBoxApi:listFolder(path, token)
         table.insert(dropbox_list, {
             text = files.text,
             url = files.url,
-            type = files.type
+            type = files.type,
         })
     end
     return dropbox_list

frontend/apps/cloudstorage/ftpapi.lua

@@ -38,7 +38,7 @@ function FtpApi:listFolder(address_path,folder_path)
                     type = type,
                 })
             --show only file with supported formats
-            elseif extension  and DocumentRegistry:getProvider(item) then
+            elseif extension  and DocumentRegistry:hasProvider(item) then
                 type = "file"
                 table.insert(ftp_file, {
                     text = file_name,

frontend/apps/filemanager/filemanager.lua

@@ -149,7 +149,7 @@ function FileManager:init()
         has_close_button = true,
         perpage = G_reader_settings:readSetting("items_per_page"),
         file_filter = function(filename)
-            if DocumentRegistry:getProvider(filename) then
+            if DocumentRegistry:hasProvider(filename) then
                 return true
             end
         end,
@@ -631,14 +631,14 @@ function FileManager:deleteFile(file)
         return
     end
 
-    local is_doc = DocumentRegistry:getProvider(file_abs_path)
+    local is_doc = DocumentRegistry:hasProvider(file_abs_path)
     if lfs.attributes(file_abs_path, "mode") == "file" then
         ok, err = os.remove(file_abs_path)
     else
         ok, err = util.purgeDir(file_abs_path)
     end
-    if ok and err == nil then
-        if is_doc ~= nil then
+    if ok and not err then
+        if is_doc then
             DocSettings:open(file):purge()
         end
         UIManager:show(InfoMessage:new{

frontend/apps/filemanager/filemanagerfilesearcher.lua

@@ -41,7 +41,7 @@ function FileSearcher:readDir()
                 if attributes.mode == "directory" and f ~= "." and f~=".." then
                     table.insert(new_dirs, fullpath)
                     table.insert(self.files, {name = f, path = fullpath, attr = attributes})
-                elseif attributes.mode == "file" and DocumentRegistry:getProvider(fullpath) then
+                elseif attributes.mode == "file" and DocumentRegistry:hasProvider(fullpath) then
                     table.insert(self.files, {name = f, path = fullpath, attr = attributes})
                 end
             end

frontend/apps/filemanager/filemanagersearch.lua

@@ -346,7 +346,7 @@ function Search:find(option)
                             self.browse_tags[string.sub(j,2)] = (self.browse_tags[string.sub(j,2)] or 0) + 1
                         end
                     end
-                    if DocumentRegistry:getProvider(self.data[i][self.path]) then
+                    if DocumentRegistry:hasProvider(self.data[i][self.path]) then
                         if upsearch ~= "" then
                             if string.find(search_content,upsearch,nil,true) then
                                 i = i + 1

frontend/document/documentregistry.lua

@@ -13,6 +13,7 @@ local T = require("ffi/util").template
 local DocumentRegistry = {
     registry = {},
     providers = {},
+    filetype_provider = {},
 }
 
 function DocumentRegistry:addProvider(extension, mimetype, provider, weight)
@@ -22,6 +23,19 @@ function DocumentRegistry:addProvider(extension, mimetype, provider, weight)
         provider = provider,
         weight = weight or 100,
     })
+    self.filetype_provider[extension] = true
+end
+
+--- Returns true if file has provider.
+-- @string file
+-- @treturn boolean
+function DocumentRegistry:hasProvider(file)
+    local filename_suffix = util.getFileNameSuffix(file)
+
+    if self.filetype_provider[filename_suffix] then
+        return true
+    end
+    return false
 end
 
 --- Returns the preferred registered document handler.
@@ -32,12 +46,14 @@ function DocumentRegistry:getProvider(file)
 
     if providers then
         -- provider for document
-        local doc_settings_provider = require("docsettings"):open(file):readSetting("provider")
-
-        if doc_settings_provider then
-            for _, provider in ipairs(providers) do
-                if provider.provider.provider == doc_settings_provider then
-                    return provider.provider
+        local DocSettings = require("docsettings")
+        if DocSettings:hasSidecarFile(file) then
+            local doc_settings_provider = DocSettings:open(file):readSetting("provider")
+            if doc_settings_provider then
+                for _, provider in ipairs(providers) do
+                    if provider.provider.provider == doc_settings_provider then
+                        return provider.provider
+                    end
                 end
             end
         end

spec/unit/document_registry_spec.lua

@@ -16,10 +16,10 @@ describe("document registry module", function()
 
     it("should return all supported rendering engines", function()
         local providers = DocumentRegistry:getProviders("bla.epub")
-        assert.is_equal("Cool Reader Engine",
-                        providers[1].provider.provider_name)
-        assert.is_equal("MuPDF",
-                        providers[2].provider.provider_name)
+        assert.is_equal("crengine",
+                        providers[1].provider.provider)
+        assert.is_equal("mupdf",
+                        providers[2].provider.provider)
     end)
 
     it("should set per-document setting for rendering engine", function()