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Display parse tree for debugging purposes

  • Trying Implement toString with Xtext's Serializer. The parse tree I get is flat without indentation when not doing the toString replacement magic, just overriding AdditionImpl.toString(). So displaying the parse tree of 1+2 just gives 1+2. (I had to use the built-in lexer, it doesn't seem to work with my external beaver-based lexer.)
  • Display parse tree with structure

Overriding nextToken() in Lexer is not enough.

The parser seems to use only the first token when building the AST.

  • There are some differences between the token returned by the internal lexer and the token by the aptana lexer. The differences include: whitespace handling; EOF; type/id of operators.
  • The difference of whitespace and EOF handling seem to cause no problem.

Why is the type of operators different in BeaverToken?

  • A literal '+' within a rule is not the same as using PLUS within the same rule. (Note: the aptana lexer returns a MATH token both for '*' and for '/')

How to vizualize the LALR grammar of coffeescript?

  • I asked about [visualizing LALR grammar] on Stackoverflow
  • I found GOLD parser which has an IDE, but runs only on Windows. But I may check it out.

Learning ANTLR

  • Tried to use the generated python target, but it seemed difficult on Ubuntu: there is no python binding for antlr3, the java version doesn't match with the downloadable python bundles. So I abandon this track, and go back to painful old java.
  • The difficulty seems to be left-factoring expressions. I asked for help with left-factoring expressions at Stackoverflow.
  • I got an answer to my question which doesn't fix the problem but helped me understand it. The issue boils down to this: write a simple expression language with function calls. An expression can be an operation or a function call. The operand in an operation can be any expression, including a function call.
  • The lesson learned is this: if I have expression: operation | whatever, and whatever can be reached via operation, then omit it from the right-hand side of expression.
  • I'm not sure how close I can stay to the original LR grammar.

Convert Antlr grammar to Xtext

See Convert Antlr grammar to Xtext

  • Terminals should be prefixed with terminal
  • The first rule should be the root, it cannot be a terminal
  • Fix the error Cannot create datatype X by including import "http://www.eclipse.org/emf/2002/Ecore" as ecore right after the first line
  • Fix the error Generated package X may not be empty by including a feature in the root rule. If you have Root: Foo, replace it with Root: bar=Foo.
  • Rules are case-insensitive, you cannot have a terminal ID and a rule Id in the same file.
  • Optionally you may want to capitalize the rule names to follow the java convention.

Running headless with make

  • I'm going to abandod this because eclipse packages are versioned with a build date too which is difficult to handle in a Makefile.
  • Possible (and time-consuming) solutions are
    • use some dependency management tool, such as ivy
    • do some bash scripting magic to find foo-[version]-v[build-date].jar and copy it as foo-[version].jar

Terminals in a separate file.

Well, I've struggled with it. Abandoned, it's not worth the effort.

Partial parsing instead of failure

1 = 2 should fail, but it the first token gets parsed, the rest discarded without any error message.

Done, using org.eclipse.xtext.junit.AbstractXtextTests.getModelAndExpect()

How is THEN handled?

Fortunately, it seems to be handled by the lexer, making it a block

Add postfix conditional.

The problem is "num = 2 if even" is parsed as an assignment "num = 2", then the next IF token is considered an error. It may be handled the same way as the existence operator.

  • Study XBase to see how they handle expressions. This is how to get to the XBase grammar:
    • Create a new XText project
    • Append with org.eclipse.xtext.xbase.Xbase to the grammar definition line
    • Navigate to Xbase and press F3

My first impression is they follow this strategy

  • Sort every rule related to expressions by its precedence
  • Create a chain of rules from lowest to highest precedence
  • The highest precendenc rule refers to PrimaryExpression
  • PrimaryExpression has all the expressions which consume at least one token from the stream

I don't know why unary expression is included in the chain, and not in the PrimaryExpression.

  • Some grammar features worth studying
    • Cross-reference denoted as [Foo], for example 'Class: class' name=ID 'extends' superClass=[Class]; The referrred [Class] will not create a new class name, but expects an existing name
    • Syntactic predicate denoted as =>.

Debugging Xtext grammar with Antlrworks

  • The grammar generated doesn't compile, it's looking for a class DebugAbstractInternalAntlrParser which cannot be found anywhere
  • Xtext claims to have new stuff for debugging. New stuff includes a railroad diagram (Views->Xtext->Xtext Syntax Graph). It also refers to a new generator fragment, org.eclipse.xtext.generator.parser.antlr.DebugAntlrGeneratorFragment which I don't know yet how to use.
  • It was just a single line of code, and csep/src-gen/csep/parser/antlr/internal/DebugInternalCoffeeScript.g gets generated which can be opened and debugged with Antlrworks seamlessly

Warning: "Decision can match input such as RULE_IF using multiple alternatives: 1, 2"

  • Before the previous commit it almost disappeared, then it came back.
  • The answer to this Stackoverflow question says, you can set option=greedy in Antlr, but this is not an option here, because the Antlr grammar is generated.
  • This issue has no impact on parsing itself, it affects only the way how AST will be constructed. So I'm going to deal with this question later, in the AST construction phase.
  • A dirty quick-fix in the generated DebugInternalCoffeeScript is to make this change: in rulePostfixIf append a caret to (RULE_POSTIF|RULE_IF), so it becomes (RULE_POSTIF|RULE_IF)^. I don't know how to achieve this in the Xtext grammar. I don't know why this fixes the Antlr grammar, either.

Handle dynamic variables.

It's more difficult than it first seemed, see my Stackoverflow question about handling dynamic variables

  • There is a difference between the generated debug grammar and the generated proper grammar, even to the extent that the debug grammar works, the proper one doesn't compile. See my question at Stackoverflow for more.

  • Just installed an Antlr Eclipse plugin to compare the grammars

  • I found the reason:

    Assignment: {Assignment} (=>(left...));

The {Assignment} part will be converted to an action in the internal grammar, and to an empty group before the syntactic predicate in the stripped off grammary, and to nothing in the debug grammar. The empty group seems to invalidate the syntactic predicate. I removed the {Assignment}, so an uglier AST will be produced.

  • Another trick I tried for assignment is to treat property assignment differently, so a.b = 3 is thought of as a (.b =) 3. The actual Xtext is

    Assignment returns Expression: {Assignment} (=>(left=(Id | Array) operator=(EQUAL | COMPOUND_ASSIGN)) right=Expression) | LogicOp (=>({PropertyAssignment.left=current} prop=PropertyAccess operator=EQUAL) right=Expression)?;

Unfortunately, it gives the same non-LL(*) decision error.

Linking.

Introduced IdRef and a dummy scoping mechanism. It shuts up linking problems and enables most coffeescript constructs. The only drawback for the moment seems to be that variables cannot be reassigned. It causes some tricky hidden problems (StringIndexOutOfBoundsException), so I'm going another way See http://www.eclipse.org/forums/index.php?t=msg&th=172032&start=0& and http://zarnekow.blogspot.com/2010/06/customizing-error-messages-in-xtext-10.html

Syntax highlight of keywords.

It should be automatic, but it matters how terminals are defined in the grammar, consider this:

ImportStatement: 'import' ID;

ExportStatement: EXPORT ID;
terminal EXPORT: 'export';

In the first case, import will be a Keyword object; in the second case, it will be a Terminal object.

There is a way to assign a highlighting category to each token, see http://www.eclipse.org/forums/index.php?t=msg&goto=479001& This is what I just started. Regex can be configured in the preferences now, but it doesn't get highlighted in the source code.

Tricky highlight issues

  • how to handle 'then' which doesn't get a token, but is replaced with a block?
  • how to handle string interpolation? "before #{ x } after" is tokenized as [( (] [STRING "before "] [+ +] [IDENTIFIER x] [+ +] [STRING " after"] [) )]

Variable scoping. The strategy is

  • The left-hand side of assignment contains Id. It causes a Duplicate ForValue error in case of reassignment. Solution: simply hide this error.
  • The right-hand side of assignment contains IdRef. It causes a Couldn't resolve reference to xxx error when using an imported or built-in object. Solution: change this error to a warning. Optionally, add built-in objects to global scope.
  • Change compound left-hand sides to contain only Ids. It means introducing new rules: AssignableArray and AssignableObject. It wouldn't accept syntactically correct, but erroneous expressions, such as [a+1] = 3

Syntax highlight of comments

Xtext uses TokenScanner when doing syntax highlighting which seems to ignore the lexer and to use the xtext grammar directly. I asked about it: http://www.eclipse.org/forums/index.php/m/772060/#msg\_772060 I may check out semantic highlighting instead.

It was easier to change the terminals in the xtext grammar and stay with the current lexical highlighter.

Display tokenization errors correctly.

An exception may be thrown either by the scanner, or by the rewriter. In the first case, we have a stream of valid tokens up to the point where the exception was thrown. In the second case, the rewriter iterates over the tokens, so we need to throw an exception containing the index of the problematic token. Eclipse doesn't treat INVALID_TOKEN_TYPE in a special way, just passes it on to the parser. So it would be correct if the Lexer added a Diagnostic error directly to the XtextResource.

The errors in XtextResource are cleared in the parsing phase, so adding a Diagnostic error by the lexer would be lost.

Issues

  • One-character long string not recognized in editor -- Done
  • Double quotation mark within singly quoted string -- Done
  • Add standard objects and functions (Array, String, Math, console, etc) to global scope
  • Add function parameters to local scope, they should be Id-s rather than IdRef-s
  • Explore StringIndexOutOfBoundsException problem when resolving an xtext link -- Done
  • break keyword -- Done
  • Comments are ignored by lexer, so error locations are shifted by the length of preceding comment -- Done
  • Weird reconciler exception when opening nodes.coffee -- Done
  • Use .coffee as file extension -- Done
  • Accept empty file

The file has to be modified to activate xtext grammar check

Problems with tokens got from Aptana scanner

  • It uses short numbers internally which easily overflows, resulting token positions restarted after 4095 -- oops, not true, it simply uses offsets
  • The rewriter calculates wrong positions for inserted tokens, sometimes resulting in a token with startIndex > stopIndex
  • Comments get ignored, since it can't use a hidden channel (probably unsupported by the Beaver API)
  • It doesn't seem to keep track of line number and positions within line

The case of the ugly StringIndexOutOfBoundsException:

When an issue is raised, its content is calculated from the whole text indexed by the token where occurred. But the whole text is calculated by taking the input char stream and reading it from the first token. If the first token was hidden, the beginning of the text is chopped, and we'll get a shorter full text. So a substring with the proper indexes will fail.

Most annoying issue:

The editor works inconsistently.

  • Sometimes No viable alternative at EOF for an empty or almost empty file
  • When opening a file, it's not checked, only after it's been modified
  • Saving a file removes warnings
  • The warnings are not shown in the Problems window

Hovering sometimes throws an NPE, maybe when I hover over a missing crossref

Scoping, second round.

Reading this series of posts: http://blogs.itemis.de/stundzig/archives/773 I just realized that functions have dynamic scoping, but loops seem to have lexical scoping.

Debugging into AbstractDeclarativeScopeProvider and ImportedNamespaceAwareLocalScopeProvider makes me think that scopes are queries based on how AST nodes are nested. I suspect that my IdRef references are hidden in a side-branch in the AST, so their referees cannot be found by simply querying upwards. My next step could be just to make this work properly

 a = 0
 b = a + 1

Built-in namespaces/objects. I have to make import (aka. require) work in the first place. Then I can think about default global imports. Well, it seems to much work to do it properly, resolve exports in the imported file, etc. It would add only a limited autocompletion support, anyway, since we can't infer the return type of a function call.

Read original coffeescript source files. There seems to be some errors with scanner which cannot handle all of them properly.

Probably interdependent issues

  • Files don't get validated automatically (http://www.eclipse.org/forums/index.php/m/774437/#msg\_774437)
  • Errors are not displayed in the Problems tab
    • Well, maybe a workaround, but you can manually validate the file selecting Validate from the context menu.
  • Saving or modifying a file may change whether or not problems are shown in the editor

An ugly bug that took me hours to hunt down

When there's an error in the file, any change to the file will generate a number of errors without any message. This is due to the bug that somewhere deep down trailing zero bytes are appended to the source text to be parsed. My hunch is it's related to replacing the text from the previous parse result using a replace region. I couldn't find the exact source of the problem, but could make a simple workaround.

Auto-completion

The tricky thing is: when we try to give a completion for Math., the context is an IdRef, but it can't find any referee named Math. So we have no name for the lookup.

String interpolation mystery

The right-hand side of first and second in the following snippet should be parsed the same, because the same tokens are generated.

name = "Joe"
first = ("I am " + name)
second = "I am #{name}"

But in the second case, a warning is given that the reference cannot be found. There is also an offset problem here, the warning message is Couldn't resolve reference to Id '#{na'

Annoying editor bug

This is how I could reproduce a problem most of the times (it may depend on typing speed). Enter the following snippet into an empty file

a=1
class C
   b:3

(The property b after class C will be auto-indented). Now, go back and insert a space before 1 in the first line. If it doesn't cause a syntax error, delete the space you just inserted. You are supposed to get a No viable alternative at input '}' error. In the meanwhile, the hosting Eclipse instance logs errors every now and then: PartialParsingHelper - Invalid replace region.

One cause is a bad coincidence: the scanner adds OUTDENT and TERMINATOR tokens with a wrong offset. The antlr stream doesn't check the upper bound. The result is: when the underlying parser gets the whole stream as string, it reads a substring after the end of the stream, resulting in trailing zero bytes.

A related problem is that the scanner added and removed some whitespaces to make its job easier, but it didn't fix the offsets accordingly.

Respond to bug reports.

Resolution warning. The minimal snippet to reproduce it is

 a = 1
 #remark
 b = a

It gives no warning when opening with a new Eclipse instance or when checking in a test case. If you add a trailing space (or if there is one, remove it), you'll get the warning. It seems to trying to resolve a as a reference, but with a wrong offset. It may be related to Xtext calculating a ReplaceRegion when parsing.

Parse element with wrong offsets are produced in XtextResource.update after calling parser.reparse()

Workaround: don't use partialParser, because it seems to be responsible for the wrong offsets. This may result in some performance penalty for larger files.

Asked about issues at Eclipse forum

Installable plugin

I followed the instructions on How to create an update site Now all you have to do is

  • Open the csep.update project
  • Open site.xml
  • Go to the Site Map tab
  • Click Build all

The csep.update directory will be populated with the required artifacts.

Directories are cleaned by org.eclipse.emf.mwe.utils.DirectoryCleaner before generating source

The cleaner ignores .csvignore files by default, so I put such files into xxx-gen folders as a workaround to have empty directories (not tracked by mercurial).

This whole plugin development with xtext looks a pile of undocumented, overcomplicated crap

My question is http://www.eclipse.org/forums/index.php/m/795597/

Eclipse plugin versioning.

I want to append date to version number automatically. It would make plugin development easier: no need to remove and reinstall it, just update it.

Mercurial keyword substitution wouldn't solve this. It would need a special marker which would conflict with the syntax of the manifest file. It would be also difficult to put the most recent tag or current date into it.

Note: site.xml gets rewritten when building if the version number ends with "qualifier". It's a bit awkward, but never mind, the generated timestamp will be appended, and commited to the repo.

A better (but only local) solution is to have this in your .hgrc file. It will keep the commited site.xml file intact from timestamps.

[encode]
csep.update/site.xml = sed -e '/feature url/ s/[0-9]\{12\}/qualifier/g'

Asked http://stackoverflow.com/questions/9535064/

Problem with generated folders again

Eclipse gives a warning "the resource is a duplicate of ..." I added some comment to the .csvignore files causing the problem -- no change. I followed the advice of http://www.stevenmarkford.com/solution-to-eclipse-warning-with-svn-the-resource-is-a-duplicate-of-and-was-not-copied-to-the-output-folder/ -- no change. Leaving it as is, for now.

Update site

It's difficult to find a hosting site, because download folders are required. Most open source hosting sites don't provide this. The only exception may be Sourceforge, but I haven't checked it, I don't want to register. I tried to have an update site with a flat file structure, but I couldn't make it work.

I'm going to host it at eclipselabs at googlecode, it seems an appropriate place. It has no ability to create download directories, either, so I'll have to put it into a mercurial repository, but 2GB should be enough -- well, it still feels a bit awkward to use a repository to store a few binary files.

Create a coffee plugin so the language can be extended

Cakefile language is almost the same as coffee with a single addition: it has task as a predefined function. It requires two steps to make it work

  1. Do magic in coffeescript plugin so its extensions will know about the language
  2. Do magic in cakefile application to know about coffeescript

How other projects make use of the Xbase language? I created a new example project Xtext -> Domainmodel. Its mwe2 file contains this

bean = StandaloneSetup {
  // ...
  registerGeneratedEPackage = "org.eclipse.xtext.xbase.XbasePackage"
  registerGenModelFile = "platform:/resource/org.eclipse.xtext.xbase/model/Xbase.genmodel"
}

I had to understand how the mwe2 workflow works. After that I realized that magic 1 puts a genmodel file to a strange URL, then magic 2 can find it there. The concepts of genmodel and ecore which are part of the magic are part of the EMF infrastructure.

Checking the xbase jar, I found that the genmodel file is actually in the model directory, but I don't know how it got there. Browsing the xbase source sheds no light on it.

I debugged how registered genmodel files are resolved: org.eclipse.emf.ecore.plugin.EcorePlugin.resolvePlatformResourcePath thinks its root location is the csep project directory in the file system. The reason may be that the csep project is in the same workspace as the cakefile project. Moving the latter into its own workspace may solve the problem.

Moving to a separate workspace doesn't solve the problem. EcorePlugin.platformResourceMap gets populated with an entry pointing to the csep directory, and this happens in a strange way before reaching any debugger break point. The platformResourceMap seems to get populated while executing org.eclipse.emf.mwe2.language.factory.SettingProviderImpl.getSettings. More precisely, while executing org.eclipse.emf.mwe.utils.StandaloneSetup.setScanClassPath.

I also bumped into a related question in the Xtext FAQ.

Reexporting the required csep and csep.ui bundles in the manifest fixes the classpath, so StandaloneSetup.setScanClassPath registers the correct jar file. But the final exception thrown remains the same.

SettingProviderImpl.getSettings calls StandaloneSetup.setScanClassPath which registers the package correctly. Then it calls StandaloneSetup.setPlatformUri which scans the folders for .project file, so re-registers the csep package incorrectly. It works based on the location of the project files, not on the workspace. Moving the whole example source tree to a separate directory may help.

It seems to fix the problem, the coffeescript genmodel is now registered correctly.

Some warnings probably not to be fixed

"Discouraged access: The type CoffeeScriptActivator is not accessible due to restriction on required project csep.ui" in in csep.tests/src-gen/csep/CoffeeScriptUiInjectorProvider.java It's generated code, I don't know how to fix it.

"The resource is a duplicate of src-gen/.cvsignore and was not copied to the output folder". A possible solution would be to remove all .cvsignore files, create a DirectoryCreator component, and add it to the mwe2 workflow:

component = DirectoryCreator {
  directory = "${runtimeProject}/src-gen"
}
// do the same for xtend-gen for ui and tests directories

"Version '0.2.1.qualifier' of plug-in 'csep.ui' is not available". It seems to work exactly this way. I may come back to it later when fine-tuning the update site.

One warning I fixed: Java execution environment warning.

  • Right click on JRE System Library in the package explorer
  • Select JavaSE-1.6 from the options

Serialization

My hunch is that the issue https://bitbucket.org/adamschmideg/coffeescript-eclipse/issue/7 is related to serialization. Partly, because a NPE is involved. If I omit serialization from the mwe2 workflow, the generation works fine, but the above issue is present. If I I have serialization in the workflow, it writes an error: "constraint is INVALID for context Block and type Body" (it's written by org.eclipse.xtext.serializer.analysis.GrammarConstraintProvider.getConstraints). If I even set generateDebugData in it, a NPE is thrown.

Use coffee lexer for cakefile

The generated tokens seem to have a different integer value for coffee and cakefile. I implemented a mindless mapping, see csep.example.cake.parser.TokenTypeMapper. It maps between coffee and cakefile tokens (both used in different cases).

Map grammar-specific identifiers ('task' in this case) are mapped to an appropriate terminal rule by csep.example.cake.parser.CustomLexer.nextToken

Implicit parameter

I want to use options either explicitly, or implicitly:

# Implicit
task "foo", "desc", ->
  # OK, implicit variable
  options.foo
  # Invalid, reference to unknown variable
  opts.foo

# Explicit
task "foo", "desc", (opts) ->
  # OK
  opts.foo
  # Invalid when options provided explicitly
  options.foo

I'm not even sure if these links are relevant

Change generated constructor in postprocessing

Not sure if it works, this phase may come later than scoping/linking. Anyway, I'm trying to change the constructor of TaskDeclaration to give a default value to options. Some examples

Well, the postprocessing approach probably wouldn't work, because it doesn't take care of scoping.

Custom scoping

I added custom declarative scoping. I have two problems with it

  • If the variable in question is not an implicit one, I just want to fall back on normal scoping. But I don't know how to get the variable name from an EReference. I may need a custom linking service that would pass the Node when calling getScope
  • What scope should I return for an implicit variable? My question at the Eclipse forum: http://www.eclipse.org/forums/index.php/mv/msg/309869/821018/#msg_821018

Consecutive assignments as nested scopes

This would handle re-assignment correctly.

a = 1         # scope 1
b = 2         # scope 2
doSomething() # same scope as before
a = a + 1     # new scope shadowing variable `a`
useVar(a)     # same scope as before, using re-assigned `a`

This may more elegant than the way it's currently implemented, but it can wait.

Error in editor: <some uri> contains a dangling reference

I implemented custom scoping. Now the above error is shown only in the editor, but the test case with implicit variable runs without any problem. I realized that scope\_Id method doesn't have to know the name of the id. It's enough to return a scope which

  • has a single options entry
  • has a reference to its parent scope -- not accessible in the method context

This wouldn't solve the dangling reference problem, anyway, which may be related to this forum entry: http://www.eclipse.org/forums/index.php/m/756325/ The problem is that I just create an Id object with options as name, but I don't register it into... I don't know what, maybe a resource. Part of this registration may create an uri for it.

I found the line that puts in the error message (I don't why zgrep didn't find it any jar file in the eclipse plugins directory). It's org.eclipse.emf.ecore.util.EObjectValidator.validate\_EveryReferenceIsContained when its eObject paramater is an IdRefImpl. The cause is that these conditions exist for the referenced IdImpl (which is the Id object named options)

  • IdImpl.eResource() == null
  • IdImpl.eIsProxy() == false

Now the question is: how are these properties set for ids? It's done in org.eclipse.xtext.resource.XtextResource.updateInternalState(IParseResult) when calling getContents().add(..., parseResult...) It calls indirectly org.eclipse.emf.ecore.impl.BasicEObjectImpl.eSetResource. So I choose to override updateInternalState and add implicit variables to the resource.

This last approach seems to work.

Include source in plugin bundle

There seems to be two ways to do it, but none of them works for me:

Timestamp issue

See https://bitbucket.org/adamschmideg/coffeescript-eclipse/issue/6 It's caused by the missing last-modified entry in the http header returned by the googlecode mercurial front-end. Set to wontfix.

Use branches on github

I don't see an easy way to convert hg branches to git branches. It would involve creating a hg bookmark for each hg branch which is otherwise discouraged. So I'm going to use a single master branch on github until a better solution is found.