Fix the issue with coverage inside of a TypeApply (#18420)

Based on looking into the issues that:
#17239 was trying to solve.

It was discovered that `TypeApply` was throwing away parts of the
expression tree, which meant that the `coverage` file contained
references to things that could never be invoked.

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

@@ -234,8 +234,8 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
             val InstrumentedParts(pre, coverageCall, expr) = tryInstrument(fun)
 
             if coverageCall.isEmpty then
-              // `fun` cannot be instrumented, and `args` is a type so we keep this tree as it is
-              tree
+              // `fun` cannot be instrumented and `args` is a type, but `expr` may have been transformed
+              cpy.TypeApply(tree)(expr, args)
             else
               // expr[T] shouldn't be transformed to:
               // {invoked(...), expr}[T]

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

@@ -17,6 +17,8 @@ import scala.language.unsafeNulls
 import scala.collection.mutable.Buffer
 import dotty.tools.dotc.util.DiffUtil
 
+import java.util.stream.Collectors
+
 @Category(Array(classOf[BootstrappedOnlyTests]))
 class CoverageTests:
   import CoverageTests.{*, given}
@@ -61,6 +63,26 @@ class CoverageTests:
           val instructions = FileDiff.diffMessage(expectFile.toString, targetFile.toString)
           fail(s"Coverage report differs from expected data.\n$instructions")
 
+      // measurement files only exist in the "run" category
+      // as these are generated at runtime by the scala.runtime.coverage.Invoker
+      val expectMeasurementFile = path.resolveSibling(s"$fileName.measurement.check")
+      if run && Files.exists(expectMeasurementFile) then
+
+        // Note that this assumes that the test invoked was single threaded,
+        // if that is not the case then this will have to be adjusted
+        val targetMeasurementFile = findMeasurementFile(targetDir)
+
+        if updateCheckFiles then
+          Files.copy(targetMeasurementFile, expectMeasurementFile, StandardCopyOption.REPLACE_EXISTING)
+
+        else
+          val targetMeasurementFile = findMeasurementFile(targetDir)
+          val expectedMeasurements = fixWindowsPaths(Files.readAllLines(expectMeasurementFile).asScala)
+          val obtainedMeasurements = fixWindowsPaths(Files.readAllLines(targetMeasurementFile).asScala)
+          if expectedMeasurements != obtainedMeasurements then
+            val instructions = FileDiff.diffMessage(expectMeasurementFile.toString, targetMeasurementFile.toString)
+            fail(s"Measurement report differs from expected data.\n$instructions")
+      ()
     })
 
   /** Generates the coverage report for the given input file, in a temporary directory. */
@@ -75,6 +97,14 @@ class CoverageTests:
       test.checkCompile()
     target
 
+  private def findMeasurementFile(targetDir: Path): Path = {
+    val allFilesInTarget = Files.list(targetDir).collect(Collectors.toList).asScala
+    allFilesInTarget.filter(_.getFileName.toString.startsWith("scoverage.measurements.")).headOption.getOrElse(
+      throw new AssertionError(s"Expected to find measurement file in targetDir [${targetDir}] but none were found.")
+    )
+  }
+
+
 object CoverageTests extends ParallelTesting:
   import scala.concurrent.duration.*
 

tests/coverage/run/type-apply/test.check

@@ -0,0 +1 @@
+List(List(1), List(2), List(3))

tests/coverage/run/type-apply/test.measurement.check

@@ -0,0 +1,7 @@
+6
+1
+3
+2
+5
+4
+0

tests/coverage/run/type-apply/test.scala

@@ -0,0 +1,5 @@
+@main
+def Test: Unit =
+  // verifies a problematic case where the TypeApply instrumentation was added to the coverage file,
+  // but was never marked as invoked
+  println(List(1,2,3).map(a => List(a)))

tests/coverage/run/type-apply/test.scoverage.check

@@ -0,0 +1,139 @@
+# 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
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+163
+201
+4
+println
+Apply
+false
+0
+false
+println(List(1,2,3).map(a => List(a)))
+
+1
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+171
+200
+4
+map
+Apply
+false
+0
+false
+List(1,2,3).map(a => List(a))
+
+2
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+171
+182
+4
+apply
+Apply
+false
+0
+false
+List(1,2,3)
+
+3
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+171
+175
+4
+List
+Ident
+false
+0
+false
+List
+
+4
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+$anonfun
+192
+199
+4
+apply
+Apply
+false
+0
+false
+List(a)
+
+5
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+$anonfun
+192
+196
+4
+List
+Ident
+false
+0
+false
+List
+
+6
+type-apply/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+0
+14
+1
+Test
+DefDef
+false
+0
+false
+@main\ndef Test
+