From 1e4bdac3ebb5a575d3c6d954c9fd7f4bbe7c5c3f Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 16 Dec 2019 10:55:49 +0100
Subject: [PATCH] Fix #7743: Widen by-name parameter termrefs in pattern
 matching translation

---
 .../dotty/tools/dotc/transform/PatternMatcher.scala    | 10 ++++++++--
 tests/pos/i7743.scala                                  |  3 +++
 2 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/i7743.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
index 6930539ec990..d799be0adc49 100644
--- a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
+++ b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
@@ -32,14 +32,20 @@ class PatternMatcher extends MiniPhase {
   override def transformMatch(tree: Match)(implicit ctx: Context): Tree =
     if (tree.isInstanceOf[InlineMatch]) tree
     else {
-      val translated = new Translator(tree.tpe, this).translateMatch(tree)
+      // Widen termrefs with underlying `=> T` types. Otherwise ElimByName will produce
+      // inconsistent types. See i7743.scala.
+      // Question: Does this need to be done more systematically, not just for pattern matches?
+      val matchType = tree.tpe.widenSingleton match
+        case ExprType(rt) => rt
+        case rt => tree.tpe
+      val translated = new Translator(matchType, this).translateMatch(tree)
 
       // check exhaustivity and unreachability
       val engine = new patmat.SpaceEngine
       engine.checkExhaustivity(tree)
       engine.checkRedundancy(tree)
 
-      translated.ensureConforms(tree.tpe)
+      translated.ensureConforms(matchType)
     }
 }
 
diff --git a/tests/pos/i7743.scala b/tests/pos/i7743.scala
new file mode 100644
index 000000000000..088f892aa206
--- /dev/null
+++ b/tests/pos/i7743.scala
@@ -0,0 +1,3 @@
+def foo(x: => String) = 1 match {
+    case _ => x
+}
\ No newline at end of file