From 0b6b8169e5105ce1c52c1c586a7384efbb8523bb Mon Sep 17 00:00:00 2001
From: Michael Davis <mcarsondavis@gmail.com>
Date: Mon, 26 Feb 2024 14:19:39 -0500
Subject: [PATCH] Skip isolating cover instructions when native coverage is
 available

If OTP is compiled with native coverage support (OTP 27+ plus JIT),
`cover` does not attempt to inject counters into the code, so
isolating the cover instructions fails. We can skip that step when we
detect native coverage support.
---
 src/horus.erl | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/horus.erl b/src/horus.erl
index b074466..88b814e 100644
--- a/src/horus.erl
+++ b/src/horus.erl
@@ -324,6 +324,19 @@ fun((#{calls := #{Call :: mfa() => true},
 
 -define(SF_ENTRYPOINT, run).
 
+-if(?OTP_RELEASE >= 27).
+-define(IF_NATIVE_COVERAGE_IS_SUPPORTED(IfSupportedBlock, ElseBlock),
+        (case code:coverage_support() of
+             true ->
+                 IfSupportedBlock;
+             false ->
+                 ElseBlock
+         end)).
+-else.
+-define(IF_NATIVE_COVERAGE_IS_SUPPORTED(_IfSupportedBlock, ElseBlock),
+        (ElseBlock)).
+-endif.
+
 -spec to_standalone_fun(Fun) -> StandaloneFun when
       Fun :: fun(),
       StandaloneFun :: horus_fun().
@@ -1218,8 +1231,17 @@ pass1_process_instructions(
   Instructions,
   #state{mfa_in_progress = MFA,
          asm_in_progress_from = cover} = State) ->
-    Instructions1 = horus_cover:isolate_cover_instructions(MFA, Instructions),
-    pass1_process_instructions(Instructions1, State, []);
+    ?IF_NATIVE_COVERAGE_IS_SUPPORTED(
+      begin
+          %% In Erlang/OTP 27+ with JIT, cover does not inject counters, so
+          %% there are no significant cover instructions to isolate.
+          pass1_process_instructions(Instructions, State, []);
+      end,
+      begin
+          Instructions1 = horus_cover:isolate_cover_instructions(
+                            MFA, Instructions),
+          pass1_process_instructions(Instructions1, State, [])
+      end);
 pass1_process_instructions(Instructions, State) ->
     pass1_process_instructions(Instructions, State, []).