Extending the Xbase Typesystem

1. Extending the Xbase Typesystem Sebastian Zarnekow

2. Understanding the Xbase TS

3. LazyLinking vs BatchLinking

4. IBatchTypeResolver Cancelable Type Resolution for a Resource Returns IResolvedTypes Type for each JvmIdentiﬁableElement (Local Var, Param, ..) Resolved Generics For each XExpression: Actual Type and Expected Type Return Type and Expected Return Type

5. Actual Type vs Return Type Type: What would ‘Extract Local Var’ do? == boolean Return Type: What would ‘Extract Method’ yield? == void {  if (!isValid(value))  return;  hashSet.add(value);  }

6. LightweightTypeReference

7. LightweightTypeReference Solve the EMF Dilemma Rich API getSuperTypes, getTypeArguments, isAssignableFrom, … Context and Service Access via getOwner() Lossless conversion from/to JvmTypeReference

8. ITypeReferenceOwner Provides Context: Current ResourceSet Provides CommonTypeComputationServices Factory API to Create Valid Type References

9. Facade for Clients Find Relevant Root Elements in Resource Traverse Root Instance Tree Guard Against Inﬁnite Recursion Prepare and Compute Traverse Expression Trees First Candidate for Customizing IBatchTypeResolver IReentrantTypeResolver ITypeComputer IBatchTypeResolver

10. IBatchTypeResolver IReentrantTypeResolver ITypeComputer  BatchLinkableResource IJvmModelInferrer InferredTypeIndicator <<installs>> <<detects>> <<initialized by>>

11. XbaseTypeComputer computeTypes(XExpression, ITypeComputationState) MyDslTypeComputer Called by the Framework Never Invoke computeTypes(..) Manually Implements Default XExpression Typing Dispatches for given XExpression Optional Customization Required for New Expressions ITypeComputer 

12. ITypeComputer  computeTypes(XExpression, ITypeComputationState) ITypeComputationState    computeTypes(XExpression): ITypeComputationResult withExpectation(LightweightTypeReference): ITCState getExpectations(): List<ITypeExpectation> acceptActualType(LightweightTypeReference, Hints) assignTypes(..): ITypeComputationState ITypeExpectation ITypeComputationResult <<yields>> <<calls>> <<uses>> <<creates>> <<inﬂuences>> <<calls>> <<uses>>

13. Type System Invariants All Expressions Must be Visited All InferredTypes Must be Resolved JvmMember Signatures Must be Complete Explicit Tree Traversal  No eAllContents.forEach in Framework Code

14. Cookbook:  Extending the Xbase TS

15. DateLiteral DateLiteral returns xbase::XExpression: day=INT ’.’ month=INT ’.’ year=INT;

16. DateLiteral Use java.util.Date (at your own risk)

17. DateLiteral class MyDslTypeComputer extends XbaseTypeComputer { def dispatch computeTypes(DateLiteral date, ITCState s) { s.acceptActualType(getTypeForName(j.u.Date, s)) } }

18. DateLiteral Support Different Date Implementations

19. Exploit Type Expectation def dispatch computeTypes(DateLiteral date, ITCState s) { for(e: s.expectations) e.acceptActualType(getTypeForName(switch it: e.expectedType { case it === null: java.util.Date // no expected type given case isType(java.sql.Date): java.sql.Date case isType(LocalDate): LocalDate // fancy Java8 impl default: java.util.Date // eeek  }, s))  }

20. DateLiteral Validate Literal Values

21. Validate Expressions def dispatch computeTypes(DateLiteral date, ITCState s) { if (isInvalid(date.day, date.month, date.year)) { s.addDiagnostic(new EObjectDiagnosticImpl(  Severity.ERROR, IssueCodes.INVALID_DATE_LITERAL,  ’’’«day».«month».«year» is not a valid date’’’,  date, null, -1, Strings.EMPTY_ARRAY));  } ..  }

22. Library Types Globally Available Types XImportSectionNamespaceScopeProvider and IImportsConﬁguration Globally Available Features ImplicitlyImportedFeatures Locally Available Features ITypeComputationState.addImports

23. Library Types def dispatch computeTypes(MyExpression e, ITCState s) { s.addImports [ ITypeImporter it | for(e: s.expectations) {  if (isEnum(e.expectedType)) { it.importStatic( e.expectedType.type as JvmEnumerationType) }  }  ] // see also s.addTypeToStaticImportScope(..)  s.computeTypes(e.childExpression)  }

24. Different Qualities of Assignability Synonyms Type A is Convertable to Type B Compiler / Interpreter Need Special Treatment Native Assignability Only Reasonable with Custom Interpreter / Runtime Assignable According to Runtime Custom Assignability Rules

25. class MySynonymTypesProvider extends SynonymTypesProvider { @Override  def boolean collectCustomSynonymTypes(LightweightTypeReference type,  Acceptor acceptor) { if (type.invariantBoundSubstitute.isType(j.t.LocalDate)) { return announceSynonym(  getUtilDate(type),  ConformanceFlags.DEMAND_CONVERSION,  acceptor); }  return true; }  } Custom Assignability Rules

26. Custom Assignability Rules TypeConformanceComputer Native Assignability Rules Uses Custom SynonymTypesProvider Common SuperType Computation Usually not Customized

27. Recap: What to customize if … JvmModelInferrer Always Put XExpression into “some” Context Mark Types as Inferred

28. Recap: What to customize if … XbaseTypeComputer Newly Introduced Expression Modiﬁed Expression Semantics

29. Recap: What to customize if … DefaultReentrantTypeResolver iff Expressions without JVM Model (Discouraged) and Expressions not at Root Level LogicalContainerAwareReentrantTypeResolver Handle AntLR Error Recovery Situations

30. Recap: What to customize if … *ReentrantTypeResolver Prepare Special Cases of InferredTypeIndicators  e.g. InferredType 1:n or 1:0 XExpression

31. Recap: What to customize if … DefaultBatchTypeResolver Non-JVM Model Entry Points on Resource Level LogicalContainerAwareBatchTypeResolver Handle AntLR Error Recovery Situations Usually Not Necessary

32. Unit Test Utility @RunWith(XtextSmokeTestRunner) @ProcessedBy(  value = TypeSystemSmokeTester,  processInParallel = true)  @SuiteClasses(ParserTest, ValidationTest)  class SmokeTest {}

33. Q & A

Extending the Xbase Typesystem

Extending the Xbase Typesystem

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