From 72a9014f711a62115c12de827226b2a8f072239b Mon Sep 17 00:00:00 2001
From: Jan Chyb <jan.chyb.99@gmail.com>
Date: Tue, 14 May 2024 12:25:27 +0200
Subject: [PATCH] Check pattern match exhaustivity in inlined code

[Cherry-picked 36d2205284b9042304204da0b4a16f13392c4a04]
---
 .../dotty/tools/dotc/transform/PatternMatcher.scala    |  4 ++++
 .../src/dotty/tools/dotc/transform/patmat/Space.scala  |  5 ++++-
 tests/warn/i20372.check                                |  8 ++++++++
 tests/warn/i20372.scala                                | 10 ++++++++++
 4 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 tests/warn/i20372.check
 create mode 100644 tests/warn/i20372.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
index 3778a263c14e..316acf02d453 100644
--- a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
@@ -56,6 +56,10 @@ class PatternMatcher extends MiniPhase {
       if !inInlinedCode then
         // check exhaustivity and unreachability
         SpaceEngine.checkMatch(tree)
+      else
+        // only check exhaustivity, as inlining may generate unreachable code 
+        // like in i19157.scala
+        SpaceEngine.checkMatchExhaustivityOnly(tree)
 
       translated.ensureConforms(matchType)
     }
diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
index 560f1d6e92e9..118b7fe70ce3 100644
--- a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
+++ b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -903,6 +903,9 @@ object SpaceEngine {
   }
 
   def checkMatch(m: Match)(using Context): Unit =
-    if exhaustivityCheckable(m.selector) then checkExhaustivity(m)
+    checkMatchExhaustivityOnly(m)
     if reachabilityCheckable(m.selector) then checkReachability(m)
+  
+  def checkMatchExhaustivityOnly(m: Match)(using Context): Unit =
+    if exhaustivityCheckable(m.selector) then checkExhaustivity(m)
 }
diff --git a/tests/warn/i20372.check b/tests/warn/i20372.check
new file mode 100644
index 000000000000..7946c424df0c
--- /dev/null
+++ b/tests/warn/i20372.check
@@ -0,0 +1,8 @@
+-- [E029] Pattern Match Exhaustivity Warning: tests/warn/i20372.scala:8:5 ----------------------------------------------
+8 |  id(foo match { // warn
+  |     ^^^
+  |     match may not be exhaustive.
+  |
+  |     It would fail on pattern case: Baz
+  |
+  | longer explanation available when compiling with `-explain`
diff --git a/tests/warn/i20372.scala b/tests/warn/i20372.scala
new file mode 100644
index 000000000000..2886bd11b09f
--- /dev/null
+++ b/tests/warn/i20372.scala
@@ -0,0 +1,10 @@
+sealed trait Foo
+case object Bar extends Foo
+case object Baz extends Foo
+
+inline def id[A](a: A): A = a
+
+def shouldThrowAWarning(foo: Foo) =
+  id(foo match { // warn
+    case Bar => "Bar"
+  })