The Parsers in Code
Generating the parsers requires Java installed (because ANTLR is a Java tool), which is the reason why we include the generated files in the source package. This way you are not forced to install Java when you want to build MySQL Workbench. The generation step is simply skipped as the grammar and generated files have the same current timestamp. However, as soon as you change the grammar you will need Java (and the ANTLR jar) to regenerate the parser files, when you build MySQL Workbench yourself.
Starting with Workbench 6.3 we use 2 parser variants: one that generates an AST (abstract syntax tree) and one without. The latter is used for our quick syntax checker as it is twice as fast as the one generating an AST (generation cannot be switched dynamically). The AST however is needed to easily walk the parsed elements, e.g. to find the type of a statement, convert query details into our internal representation, manipulate (rewrite) queries and other things.