Type parameter variance

README.md

@@ -9,3 +9,20 @@ References
 
 * [The Scala Language Specification](http://www.scala-lang.org/docu/files/ScalaReference.pdf)
 * [Scala Syntax Summary](https://www.scala-lang.org/files/archive/spec/2.11/13-syntax-summary.html)
+
+Development
+-----------
+
+First, install the project's dependencies:
+
+```sh
+npm install
+```
+
+Add a test case to `./corpus`, make the required changes to `grammar.js`,
+regenerate and recompile the parser, and run the tests:
+
+```sh
+npm run build
+npm test
+```

corpus/definitions.txt

@@ -1,11 +1,44 @@
+================================
+Package
+================================
+
+package a.b
+package c {
+  object A
+}
+
+---
+
+(compilation_unit
+  (package_clause (package_identifier (identifier) (identifier)))
+  (package_clause (package_identifier (identifier))
+    (template_body
+      (object_definition (identifier)))))
+
+================================
+Package object
+================================
+
+package object d extends A {
+  val hello: String = "there"
+}
+
+---
+
+(compilation_unit
+  (package_object
+    (identifier)
+    (extends_clause (type_identifier))
+    (template_body
+      (val_definition (identifier) (type_identifier) (string)))))
+
 ================================
 Imports
 ================================
 
 import PartialFunction.condOpt
+import a.b, c.e
 import reflect.io.{Directory, File, Path}
-import tools.nsc.classpath._
-import lang.System.{lineSeparator => EOL}
 
 ---
 
@@ -14,10 +47,33 @@ import lang.System.{lineSeparator => EOL}
     (stable_identifier (identifier) (identifier)))
   (import_declaration
     (stable_identifier (identifier) (identifier))
-    (import_selectors (identifier) (identifier) (identifier)))
+    (stable_identifier (identifier) (identifier)))
+  (import_declaration
+    (stable_identifier (identifier) (identifier))
+    (import_selectors (identifier) (identifier) (identifier))))
+
+================================
+Imports: Wildcard
+================================
+
+import tools.nsc.classpath._
+
+---
+
+(compilation_unit
   (import_declaration
     (stable_identifier (stable_identifier (identifier) (identifier)) (identifier))
-    (wildcard))
+    (wildcard)))
+
+================================
+Imports: Rename
+================================
+
+import lang.System.{lineSeparator => EOL}
+
+---
+
+(compilation_unit
   (import_declaration
     (stable_identifier (identifier) (identifier))
     (import_selectors (renamed_identifier (identifier) (identifier)))))
@@ -33,12 +89,16 @@ object O1 {
 case object O2 {
 }
 
+object O3 extends A {
+}
+
 ---
 
 (compilation_unit
   (comment)
   (object_definition (identifier) (template_body))
-  (object_definition (identifier) (template_body)))
+  (object_definition (identifier) (template_body))
+  (object_definition (identifier) (extends_clause (type_identifier)) (template_body)))
 
 =======================================
 Class definitions

corpus/types.txt

@@ -87,3 +87,83 @@ type A = B Foo C
   (type_definition
     (type_identifier)
     (infix_type (type_identifier) (identifier) (type_identifier))))
+
+
+==================================
+Variant Types
+==================================
+
+class Function1[-T1, +R]
+
+---
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (type_parameters
+      (contravariant_type_parameter (identifier))
+      (covariant_type_parameter (identifier)))))
+
+
+==================================
+Upper bound
+==================================
+
+class A[B <: C]
+
+---
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (type_parameters
+      (identifier)
+      (upper_bound (type_identifier)))))
+
+==================================
+Lower bound
+==================================
+
+class A[B >: C]
+
+---
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (type_parameters
+      (identifier)
+      (lower_bound (type_identifier)))))
+
+==================================
+View bound
+==================================
+
+
+class A[B <% C <% D]
+
+---
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (type_parameters
+      (identifier)
+      (view_bound (type_identifier))
+      (view_bound (type_identifier)))))
+
+==================================
+Context bound
+==================================
+
+class A[B : C : D]
+
+---
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (type_parameters
+      (identifier)
+      (context_bound (type_identifier))
+      (context_bound (type_identifier)))))

examples/Packages.scala

@@ -0,0 +1,9 @@
+package a.b
+package c {
+  object A
+}
+package c {
+  package object d {
+    val hello: String = "there"
+  }
+}

examples/Variance.scala

@@ -0,0 +1 @@
+class Function1[-T1, +R]

grammar.js

@@ -39,6 +39,7 @@ module.exports = grammar({
 
     _definition: $ => choice(
       $.package_clause,
+      $.package_object,
       $.class_definition,
       $.import_declaration,
       $.object_definition,
@@ -54,11 +55,30 @@ module.exports = grammar({
 
     package_clause: $ => seq(
       'package',
-      choice($.identifier, $.stable_identifier)
+      $.package_identifier,
+      // This is slightly more permissive than the EBNF in that it allows any
+      // kind of delcaration inside of the package blocks. As we're more
+      // concerned with the structure rather than the validity of the program
+      // we'll allow it.
+      optional($.template_body)
+    ),
+
+    package_identifier: $ => sep1(
+      '.', $.identifier
+    ),
+
+    package_object: $ => seq(
+      'package',
+      'object',
+      $._object_definition
     ),
 
     import_declaration: $ => seq(
       'import',
+      sep1(',', $._import_expression)
+    ),
+
+    _import_expression: $ => seq(
       choice($.stable_identifier, $.identifier),
       optional(seq(
         '.',
@@ -87,8 +107,13 @@ module.exports = grammar({
     object_definition: $ => seq(
       optional('case'),
       'object',
+      $._object_definition
+    ),
+
+    _object_definition: $ => seq(
       $.identifier,
-      $.template_body
+      optional($.extends_clause),
+      optional($.template_body),
     ),
 
     class_definition: $ => seq(
@@ -110,17 +135,51 @@ module.exports = grammar({
       $.template_body
     ),
 
+    // The EBNF makes a distinction between function type parameters and other
+    // type parameters as you can't specify variance on function type
+    // parameters. This isn't important to the structure of the AST so we don't
+    // make that distinction.
     type_parameters: $ => seq(
       '[',
-      commaSep1($._type_parameter),
+      commaSep1($._variant_type_parameter),
       ']'
     ),
 
-    _type_parameter: $ => choice(
-      '_',
-      $.identifier
+    _variant_type_parameter: $ => seq(
+      choice(
+        $.covariant_type_parameter,
+        $.contravariant_type_parameter,
+        $._type_parameter // invariant type parameter
+      )
+    ),
+
+    covariant_type_parameter: $ => seq(
+      '+',
+      $._type_parameter
     ),
 
+    contravariant_type_parameter: $ => seq(
+      '-',
+      $._type_parameter,
+    ),
+
+    _type_parameter: $ => seq(
+      choice($.wildcard, $.identifier),
+      optional($.type_parameters),
+      optional($.upper_bound),
+      optional($.lower_bound),
+      optional(repeat($.view_bound)),
+      optional(repeat($.context_bound)),
+    ),
+
+    upper_bound: $ => seq('<:', $._type),
+
+    lower_bound: $ => seq('>:', $._type),
+
+    view_bound: $ => seq('<%', $._type),
+
+    context_bound: $ => seq(':', $._type),
+
     template_body: $ => seq(
       '{',
       repeat($._definition),