Allow named tuple syntax for case class constructors.

This is a tweak to the named tuple spec. If the expected type is a case class
expand to a call of its apply method.

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1717,7 +1717,20 @@ object desugar {
         cpy.Tuple(tree)(elemValues)
     val names = elems.collect:
       case NamedArg(name, arg) => name
-    if names.isEmpty || ctx.mode.is(Mode.Pattern) then
+    val targetClassType = pt.underlyingClassRef(refinementOK = true)
+    val targetClass = targetClassType.typeSymbol
+    val isCaseClassConstr =
+      ctx.mode.isExpr
+      && targetClass.is(Case)
+      && !defn.isTupleClass(targetClass)
+      && targetClass != defn.TupleXXLClass
+      && names.hasSameLengthAs(elems) // true iff all arguments are named
+    if isCaseClassConstr then
+      import tpd.TreeOps
+      val companion = targetClass.companionModule.termRef
+        .withPrefix(targetClassType.asInstanceOf[TypeRef].prefix).asInstanceOf[TermRef]
+      Apply(TypedSplice(tpd.ref(companion).select(nme.apply)), elems).withSpan(tree.span)
+    else if names.isEmpty || ctx.mode.is(Mode.Pattern) then
       tup
     else
       def namesTuple = withModeBits(ctx.mode &~ Mode.Pattern | Mode.Type):

tests/run/json.check

@@ -0,0 +1,3 @@
+BuildDescription(true,true,.,typescript,true,null,List(null, null),List(Plugin(typescript-transform-paths,false), Plugin(typescript-transform-paths,true)),List(someValue, some-value, a value),node,CommonJS,ES2020,)
+BuildDescription(true,true,.,typescript,false,null,List(null, null),List(Plugin(typescript-transform-paths,false), Plugin(typescript-transform-paths,true)),List(),node,,ES2020,)
+BuildDescription(false,true,.,,false,.,List(null, null),List(),List(),,,,)

tests/run/json.scala

@@ -0,0 +1,72 @@
+import language.`3.7`
+import language.experimental.namedTuples
+import language.experimental.collectionLiterals
+
+case class BuildDescription(
+  declarationMap: Boolean = false,
+  esModuleInterop: Boolean = true,
+  baseUrl: String = ".",
+  rootDir: String = "",
+  declaration: Boolean = false,
+  outDir: String = ".",
+  deps: Seq[Dep] = [junitInterface, commonsIo],
+  plugins: Seq[Plugin]  = [],
+  aliases: Seq[String] = [],
+  moduleResolution: String = "",
+  module: String = "",
+  target: String = "",
+  other: String = ""
+)
+
+case class Plugin(
+  transform: String,
+  afterDeclarations: Boolean = false
+)
+
+val b1: BuildDescription = (
+  declarationMap = true,
+  esModuleInterop = true,
+  baseUrl = ".",
+  rootDir = "typescript",
+  declaration = true,
+  outDir = pubBundledOut,
+  deps = [junitInterface, commonsIo],
+  plugins  = [
+    ( transform = "typescript-transform-paths" ),
+    ( transform = "typescript-transform-paths",
+      afterDeclarations = true
+    )
+  ],
+  aliases = ["someValue", "some-value", "a value"],
+  moduleResolution = "node",
+  module = "CommonJS",
+  target = "ES2020"
+)
+
+val b2: BuildDescription = (
+  declarationMap = true,
+  baseUrl = ".",
+  rootDir = "typescript",
+  outDir = pubBundledOut,
+  plugins  = [
+    ( transform = "typescript-transform-paths" ),
+    ( transform = "typescript-transform-paths",
+      afterDeclarations = true
+    )
+  ],
+  moduleResolution = "node",
+  target = "ES2020"
+)
+
+val b3: BuildDescription = ()
+
+@main def Test =
+  println(b1)
+  println(b2)
+  println(b3)
+
+class Dep
+val junitInterface = Dep()
+val commonsIo = Dep()
+
+val pubBundledOut = ""