Avoid instrumentation of inline and erased definitions

These methods will not generate code and therefore do not need to be
instrumented. Note that a retained inline method will have a `$retained`
variant that will be instrumented.

Found this issue while looking into #15490.

Author: nicolasstucki

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

@@ -132,17 +132,22 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
             cpy.ValDef(tree)(rhs = rhs)
 
           case tree: DefDef =>
-            // Only transform the params (for the default values) and the rhs.
-            val paramss = transformParamss(tree.paramss)
-            val rhs = transform(tree.rhs)
-            val finalRhs =
-              if canInstrumentDefDef(tree) then
-                // Ensure that the rhs is always instrumented, if possible
-                instrumentBody(tree, rhs)
-              else
-                rhs
-            cpy.DefDef(tree)(tree.name, paramss, tree.tpt, finalRhs)
-
+            if tree.symbol.isOneOf(Inline | Erased) then
+              // Inline and erased definitions will not be in the generated code and therefore do not need to be instrumented.
+              // Note that a retained inline method will have a `$retained` variant that will be instrumented.
+              tree
+            else
+              // Only transform the params (for the default values) and the rhs.
+              val paramss = transformParamss(tree.paramss)
+              val rhs = transform(tree.rhs)
+              val finalRhs =
+                if canInstrumentDefDef(tree) then
+                  // Ensure that the rhs is always instrumented, if possible
+                  instrumentBody(tree, rhs)
+                else
+                  rhs
+              cpy.DefDef(tree)(tree.name, paramss, tree.tpt, finalRhs)
+            end if
           case tree: PackageDef =>
             // only transform the statements of the package
             cpy.PackageDef(tree)(tree.pid, transform(tree.stats))
@@ -336,4 +341,4 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
 
 object InstrumentCoverage:
   val name: String = "instrumentCoverage"
-  val description: String = "instrument code for coverage cheking"
+  val description: String = "instrument code for coverage checking"

compiler/test/dotty/tools/dotc/coverage/CoverageTests.scala

@@ -56,6 +56,7 @@ class CoverageTests:
         val expected = fixWindowsPaths(Files.readAllLines(expectFile).asScala)
         val obtained = fixWindowsPaths(Files.readAllLines(targetFile).asScala)
         if expected != obtained then
+          // FIXME: zip will drop part of the output if one is shorter (i.e. will not print anything of one is a refix of the other)
           for ((exp, actual),i) <- expected.zip(obtained).filter(_ != _).zipWithIndex do
             Console.err.println(s"wrong line ${i+1}:")
             Console.err.println(s"  expected: $exp")

tests/coverage/pos/Inlined.scoverage.check

@@ -273,71 +273,3 @@ false
 false
 def testInlined
 
-15
-Inlined.scala
-covtest
-Inlined$package$
-Object
-covtest.Inlined$package$
-assert
-288
-315
-10
-Scala3RunTime
-Select
-false
-0
-false
-scala.runtime.Scala3RunTime
-
-16
-Inlined.scala
-covtest
-Inlined$package$
-Object
-covtest.Inlined$package$
-assert
-288
-330
-10
-assertFailed
-Apply
-false
-0
-false
-scala.runtime.Scala3RunTime.assertFailed()
-
-17
-Inlined.scala
-covtest
-Inlined$package$
-Object
-covtest.Inlined$package$
-assert
-288
-330
-10
-<none>
-Block
-true
-0
-false
-scala.runtime.Scala3RunTime.assertFailed()
-
-18
-Inlined.scala
-covtest
-Inlined$package$
-Object
-covtest.Inlined$package$
-assert
-202
-231
-9
-assert
-DefDef
-false
-0
-false
-transparent inline def assert
-

tests/coverage/run/erased/test.scoverage.check

@@ -24,23 +24,6 @@ erased/test.scala
 test$package$
 Object
 <empty>.test$package$
-e
-54
-66
-2
-e
-DefDef
-false
-0
-false
-erased def e
-
-1
-erased/test.scala
-<empty>
-test$package$
-Object
-<empty>.test$package$
 foo
 149
 162
@@ -52,7 +35,7 @@ false
 false
 s"foo(a)($b)"
 
-2
+1
 erased/test.scala
 <empty>
 test$package$
@@ -69,7 +52,7 @@ false
 false
 println(s"foo(a)($b)")
 
-3
+2
 erased/test.scala
 <empty>
 test$package$
@@ -86,7 +69,7 @@ false
 false
 def foo
 
-4
+3
 erased/test.scala
 <empty>
 test$package$
@@ -103,7 +86,7 @@ false
 false
 s"identity($s)"
 
-5
+4
 erased/test.scala
 <empty>
 test$package$
@@ -120,7 +103,7 @@ false
 false
 println(s"identity($s)")
 
-6
+5
 erased/test.scala
 <empty>
 test$package$
@@ -137,7 +120,7 @@ false
 false
 def identity
 
-7
+6
 erased/test.scala
 <empty>
 test$package$
@@ -154,7 +137,7 @@ false
 false
 e("a")
 
-8
+7
 erased/test.scala
 <empty>
 test$package$
@@ -171,7 +154,7 @@ false
 false
 foo(e("a"))("b")
 
-9
+8
 erased/test.scala
 <empty>
 test$package$
@@ -188,7 +171,7 @@ false
 false
 identity("idem")
 
-10
+9
 erased/test.scala
 <empty>
 test$package$
@@ -205,7 +188,7 @@ false
 false
 foo(e("a"))(identity("idem"))
 
-11
+10
 erased/test.scala
 <empty>
 test$package$

tests/coverage/run/inline-def/test.check

@@ -0,0 +1,4 @@
+1
+foo
+bar
+foo

tests/coverage/run/inline-def/test.scala

@@ -0,0 +1,18 @@
+abstract class B:
+  val x: Int
+  def foo: String
+
+class A extends B:
+  inline val x = 1
+  inline val y = 2
+  inline def foo: String = "foo".toString
+  inline def bar: String = "bar".toString
+
+@main
+def Test: Unit =
+  val a = A()
+  println(a.x)
+  println(a.foo)
+  println(a.bar)
+  val b: B = a
+  println(b.foo)