From 4df32fc167dfca6d78b06da7e35418f1906d3e08 Mon Sep 17 00:00:00 2001
From: Kacper Korban <kacper.f.korban@gmail.com>
Date: Tue, 29 Aug 2023 14:23:06 +0200
Subject: [PATCH] Coverage: Do not lift applications of context functions

closes lampepfl#16502

[Cherry-picked 3e7dae83eb61cc0b3b3823bd372ac38ecbb49b36]
---
 .../dotc/transform/InstrumentCoverage.scala   | 15 +++-
 tests/coverage/pos/i16502.scala               |  8 ++
 tests/coverage/pos/i16502.scoverage.check     | 88 +++++++++++++++++++
 3 files changed, 109 insertions(+), 2 deletions(-)
 create mode 100644 tests/coverage/pos/i16502.scala
 create mode 100644 tests/coverage/pos/i16502.scoverage.check

diff --git a/compiler/src/dotty/tools/dotc/transform/InstrumentCoverage.scala b/compiler/src/dotty/tools/dotc/transform/InstrumentCoverage.scala
index 104c73b6c466..4adbe1313cd7 100644
--- a/compiler/src/dotty/tools/dotc/transform/InstrumentCoverage.scala
+++ b/compiler/src/dotty/tools/dotc/transform/InstrumentCoverage.scala
@@ -452,8 +452,13 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
          * they shouldn't be lifted.
          */
         val sym = fun.symbol
-        sym.exists && (isShortCircuitedOp(sym) || StringInterpolatorOpt.isCompilerIntrinsic(sym) || sym == defn.Object_synchronized)
-      end
+        sym.exists && (
+          isShortCircuitedOp(sym)
+          || StringInterpolatorOpt.isCompilerIntrinsic(sym)
+          || sym == defn.Object_synchronized
+          || isContextFunctionApply(fun)
+        )
+      end isUnliftableFun
 
       val fun = tree.fun
       val nestedApplyNeedsLift = fun match
@@ -463,6 +468,12 @@ class InstrumentCoverage extends MacroTransform with IdentityDenotTransformer:
       nestedApplyNeedsLift ||
       !isUnliftableFun(fun) && !tree.args.isEmpty && !tree.args.forall(LiftCoverage.noLift)
 
+    private def isContextFunctionApply(fun: Tree)(using Context): Boolean =
+      fun match
+        case Select(prefix, nme.apply) =>
+          defn.isContextFunctionType(prefix.tpe.widen)
+        case _ => false
+
     /** Check if an Apply can be instrumented. Prevents this phase from generating incorrect code. */
     private def canInstrumentApply(tree: Apply)(using Context): Boolean =
       def isSecondaryCtorDelegateCall: Boolean = tree.fun match
diff --git a/tests/coverage/pos/i16502.scala b/tests/coverage/pos/i16502.scala
new file mode 100644
index 000000000000..bd7847138c3f
--- /dev/null
+++ b/tests/coverage/pos/i16502.scala
@@ -0,0 +1,8 @@
+import scala.concurrent.*
+
+def asyncSum: ExecutionContext ?=> Future[Int] = Future(1)
+
+@main
+def Test(): Unit =
+  import scala.concurrent.ExecutionContext.Implicits.global
+  asyncSum
diff --git a/tests/coverage/pos/i16502.scoverage.check b/tests/coverage/pos/i16502.scoverage.check
new file mode 100644
index 000000000000..febd55de39b5
--- /dev/null
+++ b/tests/coverage/pos/i16502.scoverage.check
@@ -0,0 +1,88 @@
+# 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
+i16502.scala
+<empty>
+i16502$package$
+Object
+<empty>.i16502$package$
+$anonfun
+76
+85
+2
+apply
+Apply
+false
+0
+false
+Future(1)
+
+1
+i16502.scala
+<empty>
+i16502$package$
+Object
+<empty>.i16502$package$
+asyncSum
+27
+39
+2
+asyncSum
+DefDef
+false
+0
+false
+def asyncSum
+
+2
+i16502.scala
+<empty>
+i16502$package$
+Object
+<empty>.i16502$package$
+Test
+174
+182
+7
+apply
+Apply
+false
+0
+false
+asyncSum
+
+3
+i16502.scala
+<empty>
+i16502$package$
+Object
+<empty>.i16502$package$
+Test
+87
+101
+5
+Test
+DefDef
+false
+0
+false
+@main\ndef Test
+