Fix coverage instrumentation of Java-defined and parameterless methods

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

@@ -2,23 +2,21 @@ package dotty.tools.dotc
 package transform
 
 import java.io.File
-import java.util.concurrent.atomic.AtomicInteger
 
 import ast.tpd.*
 import collection.mutable
 import core.Flags.*
 import core.Contexts.{Context, ctx, inContext}
 import core.DenotTransformers.IdentityDenotTransformer
 import core.Symbols.{defn, Symbol}
-import core.Decorators.{toTermName, i}
 import core.Constants.Constant
 import core.NameOps.isContextFunction
 import core.Types.*
+import coverage.*
 import typer.LiftCoverage
-import util.{SourcePosition, Property}
+import util.SourcePosition
 import util.Spans.Span
-import coverage.*
-import localopt.StringInterpolatorOpt.isCompilerIntrinsic
+import localopt.StringInterpolatorOpt
 
 /** Implements code coverage by inserting calls to scala.runtime.coverage.Invoker
   * ("instruments" the source code).
@@ -44,7 +42,7 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
     val outputPath = ctx.settings.coverageOutputDir.value
 
     // Ensure the dir exists
-    val dataDir = new File(outputPath)
+    val dataDir = File(outputPath)
     val newlyCreated = dataDir.mkdirs()
 
     if !newlyCreated then
@@ -66,7 +64,16 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
         tree match
           // simple cases
           case tree: (Import | Export | Literal | This | Super | New) => tree
-          case tree if tree.isEmpty || tree.isType => tree // empty Thicket, Ident, TypTree, ...
+          case tree if tree.isEmpty || tree.isType => tree // empty Thicket, Ident (referring to a type), TypeTree, ...
+
+          // identifier
+          case tree: Ident =>
+            val sym = tree.symbol
+            if canInstrumentParameterless(sym) then
+              // call to a local parameterless method f
+              instrument(tree)
+            else
+              tree
 
           // branches
           case tree: If =>
@@ -82,20 +89,6 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
               finalizer = instrument(transform(tree.finalizer), branch = true)
             )
 
-          // a.f(args)
-          case tree @ Apply(fun: Select, args) =>
-            // don't transform the first Select, but do transform `a.b` in `a.b.f(args)`
-            val transformedFun = cpy.Select(fun)(transform(fun.qualifier), fun.name)
-            if canInstrumentApply(tree) then
-              if needsLift(tree) then
-                val transformed = cpy.Apply(tree)(transformedFun, args) // args will be transformed in instrumentLifted
-                instrumentLifted(transformed)
-              else
-                val transformed = transformApply(tree, transformedFun)
-                instrument(transformed)
-            else
-              transformApply(tree, transformedFun)
-
           // f(args)
           case tree: Apply =>
             if canInstrumentApply(tree) then
@@ -106,24 +99,19 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
             else
               transformApply(tree)
 
-          // (f(x))[args]
-          case TypeApply(fun: Apply, args) =>
+          // (fun)[args]
+          case TypeApply(fun, args) =>
             cpy.TypeApply(tree)(transform(fun), args)
 
           // a.b
           case Select(qual, name) =>
-            if qual.symbol.exists && qual.symbol.is(JavaDefined) then
-              //Java class can't be used as a value, we can't instrument the
-              //qualifier ({<Probe>;System}.xyz() is not possible !) instrument it
-              //as it is
-              instrument(tree)
+            val transformed = cpy.Select(tree)(transform(qual), name)
+            val sym = tree.symbol
+            if canInstrumentParameterless(sym) then
+              // call to a parameterless method
+              instrument(transformed)
             else
-              val transformed = cpy.Select(tree)(transform(qual), name)
-              if transformed.qualifier.isDef then
-                // instrument calls to methods without parameter list
-                instrument(transformed)
-              else
-                transformed
+              transformed
 
           case tree: CaseDef => instrumentCaseDef(tree)
           case tree: ValDef =>
@@ -142,7 +130,9 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
               val rhs = transform(tree.rhs)
               val finalRhs =
                 if canInstrumentDefDef(tree) then
-                  // Ensure that the rhs is always instrumented, if possible
+                  // Ensure that the rhs is always instrumented, if possible.
+                  // This is useful because methods can be stored and called later, or called by reflection,
+                  // and if the rhs is too simple to be instrumented (like `def f = this`), the method won't show up as covered.
                   instrumentBody(tree, rhs)
                 else
                   rhs
@@ -162,7 +152,7 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
         }
 
     /** Lifts and instruments an application.
-      * Note that if only one arg needs to be lifted, we just lift everything.
+      * Note that if only one arg needs to be lifted, we just lift everything (see LiftCoverage).
       */
     private def instrumentLifted(tree: Apply)(using Context) =
       // lifting
@@ -178,10 +168,7 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
       )
 
     private inline def transformApply(tree: Apply)(using Context): Apply =
-      transformApply(tree, transform(tree.fun))
-
-    private inline def transformApply(tree: Apply, transformedFun: Tree)(using Context): Apply =
-      cpy.Apply(tree)(transformedFun, transform(tree.args))
+      cpy.Apply(tree)(transform(tree.fun), transform(tree.args))
 
     private inline def instrumentCases(cases: List[CaseDef])(using Context): List[CaseDef] =
       cases.map(instrumentCaseDef)
@@ -201,7 +188,7 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
     private def recordStatement(tree: Tree, pos: SourcePosition, branch: Boolean)(using ctx: Context): Int =
       val id = statementId
       statementId += 1
-      val statement = new Statement(
+      val statement = Statement(
         source = ctx.source.file.name,
         location = Location(tree),
         id = id,
@@ -292,7 +279,7 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
          * they shouldn't be lifted.
          */
         val sym = fun.symbol
-        sym.exists && (isShortCircuitedOp(sym) || isCompilerIntrinsic(sym))
+        sym.exists && (isShortCircuitedOp(sym) || StringInterpolatorOpt.isCompilerIntrinsic(sym))
       end
 
       val fun = tree.fun
@@ -312,7 +299,9 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
 
     /** Check if an Apply can be instrumented. Prevents this phase from generating incorrect code. */
     private def canInstrumentApply(tree: Apply)(using Context): Boolean =
-      !tree.symbol.isOneOf(Synthetic | Artifact) && // no need to instrument synthetic apply
+      val sym = tree.symbol
+      !sym.isOneOf(Synthetic | Artifact) && // no need to instrument synthetic apply
+      !isCompilerIntrinsicMethod(sym) &&
       (tree.typeOpt match
         case AppliedType(tycon: NamedType, _) =>
           /* If the last expression in a block is a context function, we'll try to
@@ -339,6 +328,28 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
           true
       )
 
+    /** Is this the symbol of a parameterless method that we can instrument?
+      * Note: it is crucial that `asInstanceOf` and `isInstanceOf`, among others,
+      * do NOT get instrumented, because that would generate invalid code and crash
+      * in post-erasure checking.
+      */
+    private def canInstrumentParameterless(sym: Symbol)(using Context): Boolean =
+      sym.is(Method, butNot = Synthetic | Artifact) &&
+      sym.info.isParameterless &&
+      !isCompilerIntrinsicMethod(sym)
+
+    /** Does sym refer to a "compiler intrinsic" method, which only exist during compilation,
+      * like Any.isInstanceOf?
+      * If this returns true, the call souldn't be instrumented.
+      */
+    private def isCompilerIntrinsicMethod(sym: Symbol)(using Context): Boolean =
+      val owner = sym.maybeOwner
+      owner.exists && (
+        owner.eq(defn.AnyClass) ||
+        owner.isPrimitiveValueClass ||
+        owner.maybeOwner == defn.CompiletimePackageClass
+      )
+
 object InstrumentCoverage:
   val name: String = "instrumentCoverage"
   val description: String = "instrument code for coverage checking"

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

@@ -15,6 +15,7 @@ import scala.jdk.CollectionConverters.*
 import scala.util.Properties.userDir
 import scala.language.unsafeNulls
 import scala.collection.mutable.Buffer
+import dotty.tools.dotc.util.DiffUtil
 
 @Category(Array(classOf[BootstrappedOnlyTests]))
 class CoverageTests:
@@ -56,12 +57,8 @@ 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")
-            Console.err.println(s"  actual  : $actual")
-          fail(s"$targetFile differs from expected $expectFile")
+          val instructions = FileDiff.diffMessage(expectFile.toString, targetFile.toString)
+          fail(s"Coverage report differs from expected data.\n$instructions")
 
     })
 

tests/coverage/pos/CompiletimeUninitialized.scala

@@ -0,0 +1,5 @@
+package covtest
+
+import scala.compiletime.uninitialized
+class Foo:
+  var x: AnyRef = uninitialized

tests/coverage/pos/CompiletimeUninitialized.scoverage.check

@@ -0,0 +1,20 @@
+# 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
+# ------------------------------------------

tests/coverage/pos/Constructor.scoverage.check

@@ -59,6 +59,23 @@ C
 Class
 covtest.C
 <init>
+62
+63
+5
+x
+Select
+false
+0
+false
+x
+
+3
+Constructor.scala
+covtest
+C
+Class
+covtest.C
+<init>
 60
 64
 5
@@ -69,7 +86,7 @@ false
 false
 f(x)
 
-3
+4
 Constructor.scala
 covtest
 O$
@@ -86,7 +103,7 @@ false
 false
 def g
 
-4
+5
 Constructor.scala
 covtest
 O$
@@ -103,7 +120,24 @@ false
 false
 def y
 
-5
+6
+Constructor.scala
+covtest
+O$
+Object
+covtest.O$
+<init>
+112
+113
+10
+y
+Ident
+false
+0
+false
+y
+
+7
 Constructor.scala
 covtest
 O$