Retain positions of operators after desugaring

Author: Kordyjan

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

@@ -39,6 +39,9 @@ object desugar {
    */
   val MultiLineInfix: Property.Key[Unit] = Property.StickyKey()
 
+  /** An attachment for retaining information about the original span of the operator after desugaring it to Select. */
+  val OperatorSpan: Property.Key[Span] = Property.StickyKey()
+
   /** What static check should be applied to a Match? */
   enum MatchCheck {
     case None, Exhaustive, IrrefutablePatDef, IrrefutableGenFrom
@@ -1215,7 +1218,7 @@ object desugar {
       case _ => arg
     }
     def makeOp(fn: Tree, arg: Tree, selectPos: Span) =
-      val sel = Select(fn, op.name).withSpan(selectPos)
+      val sel = Select(fn, op.name).withSpan(selectPos).withAttachment(OperatorSpan, op.span)
       if (left.sourcePos.endLine < op.sourcePos.startLine)
         sel.pushAttachment(MultiLineInfix, ())
       arg match

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

@@ -419,8 +419,10 @@ object Trees {
     def nameSpan(using Context): Span =
       if span.exists then
         val point = span.point
-        if span.isSynthetic || name.toTermName == nme.ERROR then Span(point)
-        else Span(point, span.end, point)
+        getAttachment(desugar.OperatorSpan) match
+          case Some(s) => s
+          case None if span.isSynthetic || name.toTermName == nme.ERROR => Span(point)
+          case None => Span(point, span.end, point)
       else span
   }
 

tests/semanticdb/expect/RightAssociativeExtension.expect.scala

@@ -0,0 +1,6 @@
+package ext
+
+/*<-ext::RightAssociativeExtension$package.*/extension (s/*<-ext::RightAssociativeExtension$package.`:*:`().(s)*/: String/*->scala::Predef.String#*/)
+  def :*:/*<-ext::RightAssociativeExtension$package.`:*:`().*/ (i/*<-ext::RightAssociativeExtension$package.`:*:`().(i)*/: Int/*->scala::Int#*/): (String/*->scala::Predef.String#*/, Int/*->scala::Int#*/) = (/*->scala::Tuple2.apply().*/s/*->ext::RightAssociativeExtension$package.`:*:`().(s)*/, i/*->ext::RightAssociativeExtension$package.`:*:`().(i)*/)
+
+val b/*<-ext::RightAssociativeExtension$package.b.*/ = "foo" :*:/*->ext::RightAssociativeExtension$package.`:*:`().*/ 23

tests/semanticdb/expect/RightAssociativeExtension.scala

@@ -0,0 +1,6 @@
+package ext
+
+extension (s: String)
+  def :*: (i: Int): (String, Int) = (s, i)
+
+val b = "foo" :*: 23

tests/semanticdb/metac.expect

@@ -2415,6 +2415,40 @@ Occurrences:
 [31:10..31:11): T -> prefixes/M.T#
 [31:14..31:17): ??? -> scala/Predef.`???`().
 
+expect/RightAssociativeExtension.scala
+--------------------------------------
+
+Summary:
+Schema => SemanticDB v4
+Uri => RightAssociativeExtension.scala
+Text => empty
+Language => Scala
+Symbols => 5 entries
+Occurrences => 14 entries
+
+Symbols:
+ext/RightAssociativeExtension$package. => final package object ext
+ext/RightAssociativeExtension$package.`:*:`(). => method :*:
+ext/RightAssociativeExtension$package.`:*:`().(i) => param i
+ext/RightAssociativeExtension$package.`:*:`().(s) => param s
+ext/RightAssociativeExtension$package.b. => val method b
+
+Occurrences:
+[0:8..0:11): ext <- ext/
+[2:0..2:0): <- ext/RightAssociativeExtension$package.
+[2:11..2:12): s <- ext/RightAssociativeExtension$package.`:*:`().(s)
+[2:14..2:20): String -> scala/Predef.String#
+[3:6..3:9): :*: <- ext/RightAssociativeExtension$package.`:*:`().
+[3:11..3:12): i <- ext/RightAssociativeExtension$package.`:*:`().(i)
+[3:14..3:17): Int -> scala/Int#
+[3:21..3:27): String -> scala/Predef.String#
+[3:29..3:32): Int -> scala/Int#
+[3:37..3:37): -> scala/Tuple2.apply().
+[3:37..3:38): s -> ext/RightAssociativeExtension$package.`:*:`().(s)
+[3:40..3:41): i -> ext/RightAssociativeExtension$package.`:*:`().(i)
+[5:4..5:5): b <- ext/RightAssociativeExtension$package.b.
+[5:14..5:17): :*: -> ext/RightAssociativeExtension$package.`:*:`().
+
 expect/Selfs.scala
 ------------------