Merge "ustring: Handle empty charset like Lua does"

engines/LuaCommon/UstringLibrary.php

@@ -463,6 +463,10 @@ class Scribunto_LuaUstringLibrary extends Scribunto_LuaLibraryBase {
 				$re .= preg_quote( $pat[$i], '/' );
 			}
 		}
+		if ( $re === '[' || $re === '[^' ) {
+			// This is the error Lua string functions throws in this situation
+			throw new Scribunto_LuaError( "malformed pattern (missing ']')" );
+		}
 		if ( $i >= $len ) {
 			throw new Scribunto_LuaError( "Missing close-bracket for character set beginning at pattern character $ii" );
 		}

engines/LuaCommon/lualib/ustring/ustring.lua

@@ -567,6 +567,10 @@ local function find( s, cps, rawpat, pattern, init, noAnchor )
 			epp = ep + 1
 		until S.byte( rawpat, ep - 1 ) ~= 0x25 or S.byte( rawpat, ep - 2 ) == 0x25
 		local key = S.sub( rawpat, pattern.bytepos[pp], ep )
+		if key == '[]' or key == '[^]' then
+			-- This is the error Lua string functions throws in this situation
+			error( "malformed pattern (missing ']')" )
+		end
 		if charset_cache[key] then
 			local pl, cs = unpack( charset_cache[key] )
 			return pp + pl, cs

tests/engines/LuaCommon/UstringLibraryTests.lua

@@ -429,6 +429,14 @@ return testframework.getTestProvider( {
 	  args = { "fóó", '([^a-z])' },
 	  expect = { 2, 2, 'ó' }
 	},
+	{ name = 'find: empty character set', func = mw.ustring.find,
+	  args = { "fóó", '[]' },
+	  expect = "malformed pattern (missing ']')"
+	},
+	{ name = 'find: empty negated character set', func = mw.ustring.find,
+	  args = { "fóó", '[^]' },
+	  expect = "malformed pattern (missing ']')"
+	},
 
 	{ name = 'match: (1)', func = mw.ustring.match,
 	  args = { "bar fóo bar", 'f%a+' },