Skip to content

Latest commit

 

History

History
95 lines (70 loc) · 7.59 KB

README.md

File metadata and controls

95 lines (70 loc) · 7.59 KB
Raw

GSoC 2021 Final Report: Add synthetics and symbol information for semanticdb in Scala 3

Rikito Taniguchi (rikiriki1238@gmail.com)

Overview

SemanticDB is a data model for semantic information such as symbols and types in Scala programs. It is widely used for developing Scala's devtools such as scalafix and Metals. However, the SemanticDB extractor for Scala3 was a work in progress, and some features in devtools were unavailable for Scala3.

In this project, I worked on extracting more information for SemanticDB from the Scala3 compiler to improve the developer experience of Scala3. My contributions consists of mainly five parts.

  • Generate Scala3 code for SemanticDB data models
  • Support Signature information
  • Support Synthetic information
  • Support some missing fields of SymbolInformation and new Scala3 modifiers
  • Some other contributions

Work

(1) Generate Scala3 code for SemanticDB data models (completed)

The first thing I did was automating the process of generating Scala3 code from the protobuf scheme of SemanticDB.

Previously, the code for SemanticDB data models in Scala3 was copy-and-pasted and adjusted by hand to remove dependencies to ScalaPB and protobuf library (see the discussion). It was a plausible way of generating Scala3 code when all the information we extracted for SemanticDB was limited. However, once we start extracting more information for SemanticDB, we need more classes to generate, and hand-crafting all the code and maintaining them was unrealistic.

So I proposed some ways to improve the code generation process, and we decided to generate Scala code using ScalaPB and automatically adjust them for Scala3 compiler using scalafix. See the discussion.

Here's a project to generate and adjust Scala code, and generated code had been merged into dotty.

(2) Support Signature information (completed)

This is the main contribution of this project.

Signature in SemanticDB is a data structure that represents definition signatures (type information) for class, method, type, and local value. This information is consumed by, for example, metals to show inferred types as decoration, and scalafix rules that utilize type information. Previously, Scala3 doesn't extract this information, and Metals couldn't show the inferred type for Scala3 programs.

In this project, I extended Scala3 to extract signature information. The PR involves

  • Convert definition types of Scala3 into SemanticDB Types.
  • Convert Signature information of Scala3 to SemanticDB Signature
  • Pretty Print Signature information for regression testing.

The most tricky part of this work is converting complicated types such as TypeParamRef and TermParamRef, and RefinedType. In SemanticDB, they should be represented as TypeRef, TermRef, and StructuralType respectively, and they should contain the references to the symbols. However, we can't retrieve the symbol information directly from those types. Therefore we work-around it by

  • Traverse the children nodes first, construct symbol tables, and then lookup the symbol for TypeParamRef, TermParamRef, and RefinedType.
  • If the symbols are unavailable from the symbol tables, create a dummy symbol and convert it to a SemanticDB symbol.

(3) Support Synthetic infromation (not yet merged)

Synthetic is information that represents trees synthesized by the compiler. For example, Metals uses this information to show implicit parameters, show inferred type applications, and find references.

First, I summarized what kind of synthetic information we should extract because Scala3 has different syntax and semantics than Scala2. During the coding period, I submit PRs to support several synthetics, but they are not yet merged.

(4) Support some missing fields of SymbolInformation and new Scala3 modifiers

While working on this project, I realized some useful information is missing from SymbolInformation in Scala3. So I worked on it. Also, supported new Scala3 modifiers such as inline, transparent, and given.

(5) Other contributions

Links to all the contributions during GSoC

Future Work