From f49b27b4c8a8061a72dc6a830c1a67270e4289ee Mon Sep 17 00:00:00 2001
From: "John M. Higgins" <johnmatthiggins@gmail.com>
Date: Sun, 3 Sep 2023 08:38:27 -0700
Subject: [PATCH] fix: Closes #18367 `-Wconf` options are processed incorrectly

---
 .../src/dotty/tools/dotc/reporting/WConf.scala     |  2 +-
 .../tools/dotc/config/ScalaSettingsTests.scala     | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/reporting/WConf.scala b/compiler/src/dotty/tools/dotc/reporting/WConf.scala
index af1a5c0f0f47..5303ccd7f219 100644
--- a/compiler/src/dotty/tools/dotc/reporting/WConf.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/WConf.scala
@@ -106,7 +106,7 @@ object WConf:
   def fromSettings(settings: List[String]): Either[List[String], WConf] =
     if (settings.isEmpty) Right(WConf(Nil))
     else
-      val parsedConfs: List[Either[List[String], (List[MessageFilter], Action)]] = settings.map(conf =>
+      val parsedConfs: List[Either[List[String], (List[MessageFilter], Action)]] = settings.reverse.map(conf =>
         val filtersAndAction = conf.split(':')
         if filtersAndAction.length != 2 then Left(List("exactly one `:` expected (<filter>&...&<filter>:<action>)"))
         else
diff --git a/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala b/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
index 44cf83b521f4..a1014043724e 100644
--- a/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
+++ b/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
@@ -83,4 +83,18 @@ class ScalaSettingsTests:
     val nowr = new Diagnostic.Warning("This is a problem.".toMessage, util.NoSourcePosition)
     assertEquals(Action.Silent, sut.action(nowr))
 
+  @Test def `i18367 rightmost WConf flags take precedence over flags to the left`: Unit =
+    import reporting.{Action, Diagnostic}
+    val sets = new ScalaSettings
+    val args = List("-Wconf:cat=deprecation:e", "-Wconf:cat=deprecation:s")
+    val sumy = ArgsSummary(sets.defaultState, args, errors = Nil, warnings = Nil)
+    val proc = sets.processArguments(sumy, processAll = true, skipped = Nil)
+    val conf = sets.Wconf.valueIn(proc.sstate)
+    val msg  = "Don't use that!".toMessage
+    val depr = new Diagnostic.DeprecationWarning(msg, util.NoSourcePosition)
+    val sut  = reporting.WConf.fromSettings(conf).getOrElse(???)
+    assertEquals(Action.Silent, sut.action(depr))
+
+
+
 end ScalaSettingsTests