From 04b5daa2fe5c2f9dfa982922ec297a062052f46c Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 31 Aug 2026 19:29:39 +0000
Subject: [PATCH 1/2] Initial plan


From b8f2599cf37ef4b68047012bb5ecad52c0b70585 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Mon, 31 Aug 2026 19:44:02 +0000
Subject: [PATCH 2/2] Fix printing mapped types without property types

Co-authored-by: DanielRosenwasser <972891+DanielRosenwasser@users.noreply.github.com>
---
 .../hoverMappedTypePropertyJSDoc_test.go      | 11 +++++
 tsc/internal/printer/printer.go               |  8 ++--
 ...overMappedTypeWithoutPropertyType.baseline | 41 +++++++++++++++++++
 3 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 tsc/testdata/baselines/reference/fourslash/quickInfo/hoverMappedTypeWithoutPropertyType.baseline

diff --git a/tsc/internal/fourslash/tests/hoverMappedTypePropertyJSDoc_test.go b/tsc/internal/fourslash/tests/hoverMappedTypePropertyJSDoc_test.go
index 37398b3e11b75..1b79314469901 100644
--- a/tsc/internal/fourslash/tests/hoverMappedTypePropertyJSDoc_test.go
+++ b/tsc/internal/fourslash/tests/hoverMappedTypePropertyJSDoc_test.go
@@ -35,3 +35,14 @@ A.X/*2*/;
 	defer done()
 	f.VerifyBaselineHover(t)
 }
+
+func TestHoverMappedTypeWithoutPropertyType(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `
+declare function uhoh/*1*/<T>(x: { [K in keyof T] }): void;
+`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+	f.VerifyBaselineHover(t)
+}
diff --git a/tsc/internal/printer/printer.go b/tsc/internal/printer/printer.go
index ae279d9666341..ac8f4353dc668 100644
--- a/tsc/internal/printer/printer.go
+++ b/tsc/internal/printer/printer.go
@@ -2181,9 +2181,11 @@ func (p *Printer) emitMappedType(node *ast.MappedTypeNode) {
 			p.writePunctuation("?")
 		}
 	}
-	p.writePunctuation(":")
-	p.writeSpace()
-	p.emitTypeNodeOutsideExtends(node.Type)
+	if node.Type != nil {
+		p.writePunctuation(":")
+		p.writeSpace()
+		p.emitTypeNodeOutsideExtends(node.Type)
+	}
 	p.writeTrailingSemicolon()
 	if node.Members != nil {
 		if len(node.Members.Nodes) > 0 {
diff --git a/tsc/testdata/baselines/reference/fourslash/quickInfo/hoverMappedTypeWithoutPropertyType.baseline b/tsc/testdata/baselines/reference/fourslash/quickInfo/hoverMappedTypeWithoutPropertyType.baseline
new file mode 100644
index 0000000000000..7941d30d1a03f
--- /dev/null
+++ b/tsc/testdata/baselines/reference/fourslash/quickInfo/hoverMappedTypeWithoutPropertyType.baseline
@@ -0,0 +1,41 @@
+// === QuickInfo ===
+=== /hoverMappedTypeWithoutPropertyType.ts ===
+// 
+// declare function uhoh<T>(x: { [K in keyof T] }): void;
+//                  ^^^^
+// | ----------------------------------------------------------------------
+// | ```typescript
+// | function uhoh<T>(x: { [K in keyof T]; }): void
+// | ```
+// | 
+// | ----------------------------------------------------------------------
+// 
+[
+  {
+    "marker": {
+      "Position": 22,
+      "LSPosition": {
+        "line": 1,
+        "character": 21
+      },
+      "Name": "1",
+      "Data": {}
+    },
+    "item": {
+      "contents": {
+        "kind": "markdown",
+        "value": "```typescript\nfunction uhoh<T>(x: { [K in keyof T]; }): void\n```\n"
+      },
+      "range": {
+        "start": {
+          "line": 1,
+          "character": 17
+        },
+        "end": {
+          "line": 1,
+          "character": 21
+        }
+      }
+    }
+  }
+]
\ No newline at end of file