Coverage: mark case bodies as branches; don't ignore branches with synthetic spans

Marking bodies of CaseDefs as branches seems like an uncontroversial
change, it was probably an oversight.

Not ignoring synthetic spans when creating coverage calls in branches
seems like a good trade off. There might be some auto-generated `else
()` interpreted as branches, but Scala introduces quite a lot of
synthetic trees that wrap non-synthetic trees (e.g. implicit classes).
Also, it looks like Scala 2 includes those compiler-generated `else`
branches in coverage. (Another possibility here would be to also check
if the span is zero extent, but that approach would be different to the
Scala 2 one)

partial fix for lampepfl#16634

[Cherry-picked bcb2053]

Author: KacperFKorban

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

@@ -188,12 +188,9 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
      * If the tree is empty, return itself and don't instrument.
      */
     private def transformBranch(tree: Tree)(using Context): Tree =
-      import dotty.tools.dotc.core.Decorators.{show,i}
-      if tree.isEmpty || tree.span.isSynthetic then
+      if tree.isEmpty then
         // - If t.isEmpty then `transform(t) == t` always hold,
         //   so we can avoid calling transform in that case.
-        // - If tree.span.isSynthetic then the branch has been generated
-        //   by the frontend phases, so we don't want to instrument it.
         tree
       else
         val transformed = transform(tree)
@@ -353,10 +350,8 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
       // recursively transform the guard, but keep the pat
       val transformedGuard = transform(guard)
 
-      // ensure that the body is always instrumented by inserting a call to Invoker.invoked at its beginning
-      val coverageCall = createInvokeCall(tree.body, pos)
-      val transformedBody = transform(tree.body)
-      val instrumentedBody = InstrumentedParts.singleExprTree(coverageCall, transformedBody)
+      // ensure that the body is always instrumented as a branch
+      val instrumentedBody = transformBranch(tree.body)
 
       cpy.CaseDef(tree)(pat, transformedGuard, instrumentedBody)
 

tests/coverage/pos/Inlined.scoverage.check

@@ -59,6 +59,23 @@ Inlined$package$
 Object
 covtest.Inlined$package$
 testInlined
+330
+330
+10
+<none>
+Literal
+true
+0
+false
+
+
+3
+Inlined.scala
+covtest
+Inlined$package$
+Object
+covtest.Inlined$package$
+testInlined
 155
 162
 6
@@ -69,7 +86,7 @@ false
 false
 List(l)
 
-3
+4
 Inlined.scala
 covtest
 Inlined$package$
@@ -86,7 +103,7 @@ false
 false
 List
 
-4
+5
 Inlined.scala
 covtest
 Inlined$package$
@@ -103,7 +120,7 @@ false
 false
 List(l).length
 
-5
+6
 Inlined.scala
 covtest
 Inlined$package$
@@ -120,7 +137,7 @@ false
 false
 scala.runtime.Scala3RunTime.assertFailed()
 
-6
+7
 Inlined.scala
 covtest
 Inlined$package$
@@ -137,7 +154,24 @@ true
 false
 scala.runtime.Scala3RunTime.assertFailed()
 
-7
+8
+Inlined.scala
+covtest
+Inlined$package$
+Object
+covtest.Inlined$package$
+testInlined
+330
+330
+10
+<none>
+Literal
+true
+0
+false
+
+
+9
 Inlined.scala
 covtest
 Inlined$package$
@@ -154,7 +188,7 @@ false
 false
 List(l)
 
-8
+10
 Inlined.scala
 covtest
 Inlined$package$
@@ -171,7 +205,7 @@ false
 false
 List
 
-9
+11
 Inlined.scala
 covtest
 Inlined$package$
@@ -188,7 +222,7 @@ false
 false
 List(l).length
 
-10
+12
 Inlined.scala
 covtest
 Inlined$package$
@@ -205,7 +239,7 @@ false
 false
 scala.runtime.Scala3RunTime.assertFailed()
 
-11
+13
 Inlined.scala
 covtest
 Inlined$package$
@@ -222,7 +256,24 @@ true
 false
 scala.runtime.Scala3RunTime.assertFailed()
 
-12
+14
+Inlined.scala
+covtest
+Inlined$package$
+Object
+covtest.Inlined$package$
+testInlined
+330
+330
+10
+<none>
+Literal
+true
+0
+false
+
+
+15
 Inlined.scala
 covtest
 Inlined$package$

tests/coverage/pos/MatchCaseClasses.scoverage.check

@@ -25,23 +25,6 @@ MatchCaseClasses$
 Object
 covtest.MatchCaseClasses$
 f
-135
-147
-7
-<none>
-Block
-false
-0
-false
-case Pat1(0)
-
-1
-MatchCaseClasses.scala
-covtest
-MatchCaseClasses$
-Object
-covtest.MatchCaseClasses$
-f
 151
 163
 7
@@ -52,24 +35,24 @@ false
 false
 println("a")
 
-2
+1
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
 Object
 covtest.MatchCaseClasses$
 f
-168
-180
-8
+148
+163
+7
 <none>
 Block
-false
+true
 0
 false
-case Pat1(_)
+=> println("a")
 
-3
+2
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
@@ -86,24 +69,24 @@ false
 false
 println("b")
 
-4
+3
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
 Object
 covtest.MatchCaseClasses$
 f
-201
-221
-9
+181
+196
+8
 <none>
 Block
-false
+true
 0
 false
-case p @ Pat2(1, -1)
+=> println("b")
 
-5
+4
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
@@ -120,24 +103,24 @@ false
 false
 println("c")
 
-6
+5
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
 Object
 covtest.MatchCaseClasses$
 f
-242
-265
-10
+222
+237
+9
 <none>
 Block
-false
+true
 0
 false
-case Pat2(_, y: String)
+=> println("c")
 
-7
+6
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
@@ -154,7 +137,7 @@ false
 false
 println(y)
 
-8
+7
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
@@ -171,24 +154,24 @@ false
 false
 println("d")
 
-9
+8
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
 Object
 covtest.MatchCaseClasses$
 f
-309
-321
-13
+275
+304
+11
 <none>
 Block
-false
+true
 0
 false
-case p: Pat2
+println(y)\n      println("d")
 
-10
+9
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
@@ -205,24 +188,24 @@ false
 false
 println("e")
 
-11
+10
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
 Object
 covtest.MatchCaseClasses$
 f
-342
-348
-14
+322
+337
+13
 <none>
 Block
-false
+true
 0
 false
-case _
+=> println("e")
 
-12
+11
 MatchCaseClasses.scala
 covtest
 MatchCaseClasses$
@@ -239,6 +222,23 @@ false
 false
 println("other")
 
+12
+MatchCaseClasses.scala
+covtest
+MatchCaseClasses$
+Object
+covtest.MatchCaseClasses$
+f
+349
+368
+14
+<none>
+Block
+true
+0
+false
+=> println("other")
+
 13
 MatchCaseClasses.scala
 covtest