Ensure that calls to methods without parameter list are instrumented

compiler/src/dotty/tools/dotc/transform/InstrumentCoverage.scala

@@ -118,12 +118,17 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
               instrument(tree)
             else
               val transformed = cpy.Select(tree)(transform(qual), name)
-              if transformed.qualifier.isDef then
+              if transformed.symbol.is(Method) then
                 // instrument calls to methods without parameter list
                 instrument(transformed)
               else
                 transformed
 
+          // f
+          case tree: Ident if tree.symbol.is(Method) =>
+            // instrument calls to method without parameter list
+            instrument(tree)
+
           case tree: CaseDef => instrumentCaseDef(tree)
           case tree: ValDef =>
             // only transform the rhs

compiler/src/dotty/tools/dotc/typer/EtaExpansion.scala

@@ -177,10 +177,13 @@ object LiftCoverage extends LiftImpure {
    *  - all the impure arguments
    *
    * There's no need to lift the other arguments.
+   * Note: at the instrumentCoverage phase, calls to functions that have no parameter list aren't Apply,
+   * but Ident (e.g. `f` with f in scope) or Select (e.g. `A.f`).
    */
   private def noLiftArg(arg: tpd.Tree)(using Context): Boolean =
     arg match
       case a: tpd.Apply => a.symbol.is(Erased) // don't lift erased applications, but lift all others
+      case s: (tpd.Select | tpd.Ident) if s.symbol.is(Method) => s.symbol.is(Erased) // take care of calls to functions without parameter lists
       case tpd.Block(stats, expr) => stats.forall(noLiftArg) && noLiftArg(expr)
       case tpd.Inlined(_, bindings, expr) => noLiftArg(expr)
       case tpd.Typed(expr, _) => noLiftArg(expr)

tests/coverage/pos/NoParams.scala

@@ -0,0 +1,18 @@
+object A:
+  def noParam = 0
+
+object B:
+  def f(x: Any) = println("f")
+  def noParam = 0
+
+  def testSelect =
+    A.noParam // call should be instrumented
+
+  def testSelectArg =
+    f(A.noParam) // arg should be lifted and instrumented
+
+  def testIdent =
+    noParam // call should be instrumented
+
+  def testIdentArg =
+    f(noParam) // arg should be lifted and instrumented

tests/coverage/pos/NoParams.scoverage.check

@@ -0,0 +1,275 @@
+# Coverage data, format version: 3.0
+# Statement data:
+# - id
+# - source path
+# - package name
+# - class name
+# - class type (Class, Object or Trait)
+# - full class name
+# - method name
+# - start offset
+# - end offset
+# - line number
+# - symbol name
+# - tree name
+# - is branch
+# - invocations count
+# - is ignored
+# - description (can be multi-line)
+# '' sign
+# ------------------------------------------
+0
+NoParams.scala
+<empty>
+A$
+Object
+<empty>.A$
+noParam
+12
+23
+1
+noParam
+DefDef
+false
+0
+false
+def noParam
+
+1
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+f
+57
+64
+4
+println
+Ident
+false
+0
+false
+println
+
+2
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+f
+57
+69
+4
+<none>
+Apply
+false
+0
+false
+println("f")
+
+3
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+f
+41
+46
+4
+f
+DefDef
+false
+0
+false
+def f
+
+4
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+noParam
+72
+83
+5
+noParam
+DefDef
+false
+0
+false
+def noParam
+
+5
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testSelect
+112
+121
+8
+noParam
+Select
+false
+0
+false
+A.noParam
+
+6
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testSelect
+91
+105
+7
+testSelect
+DefDef
+false
+0
+false
+def testSelect
+
+7
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testSelectArg
+182
+191
+11
+noParam
+Select
+false
+0
+false
+A.noParam
+
+8
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testSelectArg
+180
+192
+11
+f
+Apply
+false
+0
+false
+f(A.noParam)
+
+9
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testSelectArg
+156
+173
+10
+testSelectArg
+DefDef
+false
+0
+false
+def testSelectArg
+
+10
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testIdent
+257
+264
+14
+noParam
+Ident
+false
+0
+false
+noParam
+
+11
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testIdent
+237
+250
+13
+testIdent
+DefDef
+false
+0
+false
+def testIdent
+
+12
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testIdentArg
+324
+331
+17
+noParam
+Ident
+false
+0
+false
+noParam
+
+13
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testIdentArg
+322
+332
+17
+f
+Apply
+false
+0
+false
+f(noParam)
+
+14
+NoParams.scala
+<empty>
+B$
+Object
+<empty>.B$
+testIdentArg
+299
+315
+16
+testIdentArg
+DefDef
+false
+0
+false
+def testIdentArg
+