From bbb1c6064ad0e61e86d389467e5b73d76afbe0f5 Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Thu, 20 Nov 2025 21:01:49 -0800
Subject: [PATCH 1/2] Single line case lambda gets a region

---
 .../src/dotty/tools/dotc/parsing/Parsers.scala    |  6 +++++-
 tests/neg/i24496.scala                            | 12 ++++++++++++
 tests/pos/i24496.scala                            | 15 +++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/i24496.scala
 create mode 100644 tests/pos/i24496.scala

diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index f44703a562f1..7bdc34bd7a7c 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -1137,7 +1137,11 @@ object Parsers {
           lookahead.skipParens()
           isArrowIndent()
         else if lookahead.token == CASE && in.featureEnabled(Feature.relaxedLambdaSyntax) then
-          Some(() => singleCaseMatch())
+          Some: () =>
+            inSepRegion(SingleLineLambda(_)):
+              singleCaseMatch()
+            .tap: _ =>
+              accept(ENDlambda)
         else
           None
       isParamsAndArrow()
diff --git a/tests/neg/i24496.scala b/tests/neg/i24496.scala
new file mode 100644
index 000000000000..d8a86cc87924
--- /dev/null
+++ b/tests/neg/i24496.scala
@@ -0,0 +1,12 @@
+import scala.language.experimental.relaxedLambdaSyntax
+
+@main def Test =
+  val list = List(1, 2, 3)
+
+  val three = list
+        .collect: case x =>
+          (x, x + 1) // error not a member of tuple
+        .toMap
+
+  val huh = list
+        .collect: x => case y => (y, y + 1) // error expecting case at x
diff --git a/tests/pos/i24496.scala b/tests/pos/i24496.scala
new file mode 100644
index 000000000000..0cd358a8d87f
--- /dev/null
+++ b/tests/pos/i24496.scala
@@ -0,0 +1,15 @@
+import scala.language.experimental.relaxedLambdaSyntax
+
+@main def Test =
+  val list = List(1, 2, 3)
+
+  val two = list
+        .collect: x => (x, x + 1)
+        .toMap
+
+  val one = list
+        .collect: case x => (x, x + 1)
+        .toMap
+
+  //val huh = list
+  //      .collect: x => case y => (y, y + 1) correctly errors expecting case at x

From 5a24b2a93a28e3e7a4afdda5fc8ca5674f71b38f Mon Sep 17 00:00:00 2001
From: Som Snytt <som.snytt@gmail.com>
Date: Sun, 23 Nov 2025 00:57:24 -0800
Subject: [PATCH 2/2] Permit indented RHS of single line case

---
 compiler/src/dotty/tools/dotc/parsing/Parsers.scala  | 3 +++
 compiler/src/dotty/tools/dotc/parsing/Scanners.scala | 2 +-
 tests/neg/i24496.scala                               | 4 ++--
 tests/pos/i24496.scala                               | 9 ++++++---
 4 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
index 7bdc34bd7a7c..d37ab3afc31c 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -3232,6 +3232,9 @@ object Parsers {
       val body = tok match
         case ARROW => atSpan(in.skipToken()):
           if exprOnly then
+            if in.token == ENDlambda then
+              in.token = NEWLINE
+              in.observeIndented()
             if in.indentSyntax && in.isAfterLineEnd && in.token != INDENT then
               warning(em"""Misleading indentation: this expression forms part of the preceding case.
                           |If this is intended, it should be indented for clarity.
diff --git a/compiler/src/dotty/tools/dotc/parsing/Scanners.scala b/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
index ec246f7a3742..82c87152be96 100644
--- a/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
+++ b/compiler/src/dotty/tools/dotc/parsing/Scanners.scala
@@ -596,7 +596,7 @@ object Scanners {
           lastWidth = r.width
           newlineIsSeparating = lastWidth <= nextWidth || r.isOutermost
           indentPrefix = r.prefix
-        case _: InString => ()
+        case _: InString | _: SingleLineLambda => ()
         case r =>
           indentIsSignificant = indentSyntax
           r.proposeKnownWidth(nextWidth, lastToken)
diff --git a/tests/neg/i24496.scala b/tests/neg/i24496.scala
index d8a86cc87924..4d5ae7d7d6d5 100644
--- a/tests/neg/i24496.scala
+++ b/tests/neg/i24496.scala
@@ -5,8 +5,8 @@ import scala.language.experimental.relaxedLambdaSyntax
 
   val three = list
         .collect: case x =>
-          (x, x + 1) // error not a member of tuple
-        .toMap
+        (x, x + 1)
+        .toMap // error value toMap is not a member of (Int, Int)
 
   val huh = list
         .collect: x => case y => (y, y + 1) // error expecting case at x
diff --git a/tests/pos/i24496.scala b/tests/pos/i24496.scala
index 0cd358a8d87f..bdef831863a6 100644
--- a/tests/pos/i24496.scala
+++ b/tests/pos/i24496.scala
@@ -3,6 +3,12 @@ import scala.language.experimental.relaxedLambdaSyntax
 @main def Test =
   val list = List(1, 2, 3)
 
+  val three = list
+        .collect: case x =>
+          val y = x + 1
+          (x, y)
+        .toMap
+
   val two = list
         .collect: x => (x, x + 1)
         .toMap
@@ -10,6 +16,3 @@ import scala.language.experimental.relaxedLambdaSyntax
   val one = list
         .collect: case x => (x, x + 1)
         .toMap
-
-  //val huh = list
-  //      .collect: x => case y => (y, y + 1) correctly errors expecting case at x