Once we have wrapped up everything we generate the last EOF token.
- When the AST is complete we actually trigger the regular semantic
- analysis process. The DoResolve method of each node in our abstract
- syntax tree will compute the result and communicate the possible
- completions by throwing an exception of type CompletionResult.
+ When the AST is complete we actually trigger the regular
+ semantic analysis process. The DoResolve method of each node
+ in our abstract syntax tree will compute the result and
+ communicate the possible completions by throwing an exception
+ of type CompletionResult.
So for example if the user type "T" and the completion is
"ToString" we return "oString".
+** Enhancing Completion
+
+ Code completion is a process that will be curated over time.
+ Just like producing good error reports or warnings is an
+ iterative process to find a good balance, the code completion
+ engine in the compiler will require tuning to find the right
+ balance for the end user.
+
+ This section explains the basic process by which you can
+ improve the code completion by using a real life sample.
+
+ Once you add the GENERATE_COMPLETION token to your grammar
+ rule, chances are, you will need to alter the grammar to
+ support COMPLETE_COMPLETION all the way up to the toplevel
+ production.
+
+ To debug this, you will want to try the completion with either
+ a sample program or with the `csharp' tool.
+
+ I use this setup:
+
+ $ csharp -v -v
+
+ This will turn on the parser debugging output and will
+ generate a lot of data when parsing its input.
+
+ To start with a new completion scheme, type your C# code and
+ then hit the tab key to trigger the completion engine. In the
+ generated output you will want to look for the first time that
+ the parser got the GENERATE_COMPLETION token, it will look
+ like this:
+
+ lex state 414 reading GENERATE_COMPLETION value {interactive}(1,35):
+
+ The first word `lex' indicates that the parser called the
+ lexer at state 414 (more on this in a second) and it got back
+ from the lexer the token GENERATE_COMPLETION. If this is a
+ kind of completion chances are, you will get an error
+ immediately as the rules at that point do not know how to cope
+ with the stream of COMPLETE_COMPLETION tokens that will
+ follow, they will look like this:
+
+ error syntax error
+ pop state 414 on error
+ pop state 805 on error
+ pop state 628 on error
+ pop state 417 on error
+
+ The first line means that the parser has entered the error
+ state and will pop states until it can find a production that
+ can deal with the error. At that point an error message will
+ be displayed.
+
+ Open the file `y.output' which describes the parser states
+ generated by jay and search for the state that was reported
+ previously in `lex' that got the GENERATE_COMPLETION:
+
+ state 414
+ object_or_collection_initializer : OPEN_BRACE . opt_member_initializer_list CLOSE_BRACE (444)
+ object_or_collection_initializer : OPEN_BRACE . member_initializer_list COMMA CLOSE_BRACE (445)
+ opt_member_initializer_list : . (446)
+
+ We now know that the parser was in the middle of parsing an
+ `object_or_collection_initializer' and had alread seen the
+ OPEN_BRACE token.
+
+ The `.' after OPEN_BRACE indicates the current state of the
+ parser, and this is where our parser got the
+ GENERATE_COMPLETION token. As you can see from the three
+ rules in this sample, support for GENERATE_COMPLETION did not
+ exist.
+
+ So we must edit the grammar to add a production for this case,
+ I made the code look like this:
+
+ member_initializer
+ [...]
+ | GENERATE_COMPLETION
+ {
+ LocatedToken lt = $1 as LocatedToken;
+ $$ = new CompletionElementInitializer (GetLocation ($1));
+ }
+ [...]
+
+ This new production creates the class
+ CompletionElementInitializer and returns this as the value for
+ this. The following is a trivial implementation that always
+ returns "foo" and "bar" as the two completions and it
+ illustrates how things work:
+
+ public class CompletionElementInitializer : CompletingExpression {
+ public CompletionElementInitializer (Location l)
+ {
+ this.loc = l;
+ }
+
+ public override Expression DoResolve (EmitContext ec)
+ {
+ string [] = new string [] { "foo", "bar" };
+ throw new CompletionResult ("", result);
+ }
+
+ //
+ // You should implement CloneTo if your CompletingExpression
+ // keeps copies to Statements or Expressions. CloneTo
+ // is used by the lambda engine, so you should always
+ // implement this
+ //
+ protected override void CloneTo (CloneContext clonectx, Expression t)
+ {
+ // We do not keep references to anything interesting
+ // so cloning is an empty operation.
+ }
+ }
+
+
+ We then rebuild our compiler:
+
+ (cd mcs/; make cs-parser.jay)
+ (cd tools/csharplib; make install)
+
+ And re-run csharp:
+
+ (cd tools/csharp; csharp -v -v)
+
+ Chances are, you will get another error, but this time it will
+ not be for the GENERATE_COMPLETION, we already handled that
+ one. This time it will be for COMPLETE_COMPLETION.
+
+ The remaining of the process is iterative: you need to locate
+ the state where this error happens. It will look like this:
+
+ lex state 623 reading COMPLETE_COMPLETION value {interactive}(1,35):
+ error syntax error
+
+ And make sure that the state can handle at this point a
+ COMPLETE_COMPLETION. When receiving COMPLETE_COMPLETION the
+ parser needs to complete constructing the parse tree, so
+ productions that handle COMPLETE_COMPLETION need to wrap
+ things up with whatever data they have available and just make
+ it so that the parser can complete.
+
+ To avoid rule duplication you can use the
+ opt_COMPLETE_COMPLETION production and append it to an
+ existing production:
+
+ foo : bar opt_COMPLETE_COMPLETION {
+ ..
+ }
+
* Miscellaneous
** Error Processing.
projects / mono.git / blobdiff