1 .SemanticDB For Scala developer tools !1 

2 . About me • Author of Scalafmt and Scalafix • Software developer at
 Scala Center • Scalameta maintainer 2 

3 . Credits • Eugene Burmako: Advanced Scala Tools team lead at Twitter • Co-maintainer of Scalameta and SemanticDB 3 

4 . Tooling 4 

5 . Scalameta • Open Source Project with 50+ contributors • Full-time developers funded by Scala Center + Twitter • 120k downloads/month for core module • !5 

6 .scalafmt 6 

7 . scalafix Rewrite and linting tool 7 

8 . We used Scalafix to perform a large-scale refactoring of our Scala codebase at Twitter with great success. – Shane Delmore, Advanced Scala Tools Team @Twitter 8 

9 . Scalafix enabled us to run refactorings in a distributed fashion, which is necessary for a codebase the size of ours. – Shane Delmore, Advanced Scala Tools Team @Twitter 9 

10 . Agenda • Compiler plugin vs. SemanticDB • Schema • Utilities • Demo !10 

11 . Build Tool -Xplugin:scalafix.jar Compiler plugin developer tools scalac !11 

12 . Build Tool -Xplugin:semanticdb.jar SemanticDB developer tools scalac *.semanticdb scalafix !12 

13 . Compiler plugins • Undocumented and unsupported internal APIs • Relevant data available in different phases • Analysis limited to single compilation run • Difficult to test and maintain !13 

14 . SemanticDB • 300 LOC protobuf schema: symbols, types, occurrences • 11.000 word specification: Scala, Java • Utilities: metacp, metac, mtags, metap • Applications: metadoc, metals, scalafix !14 

15 .Schema !15 

16 . TextDocument Uri: src/spire/math/Complex.scala Schema: SEMANTICDB3 Text: “package spire.math\n\n@…”
 Language: SCALA SymbolOccurrence: [ scala.SerialVersionUID# spire.math.Complex# … ] SymbolInformation: [ spire.math.Complex# spire.math.Complex#[T] … ] Diagnostics: […] Synthetics: […] !16 

17 . SymbolOccurence Symbol: spire.math.Complex# Range: 4:18-4:25 Role: DEFINITION !17 

18 . SymbolOccurence Symbol: spire.math.Complex#real(). Range: 10:18-10:22 Role: REFERENCE !18 

19 . SymbolInformation Kind: CLASS Language: SCALA Name: Complex Symbol: spire.math.Complex# Owner: spire.math. Type: ClassInfoType { +6 decls } Properties: final, case Annotations: scala.SerialVersionUID# Accessibility: PUBLIC !19 

20 . SymbolInformation Kind: PARAMETER Language: SCALA Name: r Symbol: spire.math.Complex#`+`(T,Semiring).(r) Owner: spire.math.Complex#`+`(T,Semiring). Type: TypeRef { Semiring[T] } Properties: implicit !20 

21 .Spec !21 

22 .Scala parameters !22 

23 .Java class !23 

24 .$ metac $ metacp Utilities $ mtags $ metap !24 

25 . metac Build SemanticDB with compiler !25 

26 . $ scalac -Xplugin:semanticdb.jar -Xstop-after:semanticdb-typer src/Complex.scala "## out $   %## META-INF $   %## semanticdb $      %## src $      %## Complex.scala.semanticdb %## src %## Complex.scala !26 

27 . $ metac src/Complex.scala "## out $   %## META-INF $   %## semanticdb $      %## src $      %## Complex.scala.semanticdb %## src %## Complex.scala !27 

28 ."## out $   %## META-INF $   %## semanticdb $      %## $      %## Complex.scala.semanticdb %## src %## Complex.scala !28 

29 . metacp Build SemanticDB with classpath !29