From 4a78852dc877e1ad945868bce57b62738e0bd02e Mon Sep 17 00:00:00 2001
From: Khang Nguyen Duy <k@ndykhang.net>
Date: Sun, 8 Nov 2026 14:59:20 +0700
Subject: [PATCH] fix completion crash on unknown tagged union payload type

---
 src/analyser/InternPool.zig       |  2 +-
 tests/lsp_features/completion.zig | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/analyser/InternPool.zig b/src/analyser/InternPool.zig
index e050203cc..d8953ad33 100644
--- a/src/analyser/InternPool.zig
+++ b/src/analyser/InternPool.zig
@@ -3655,7 +3655,7 @@ pub fn onePossibleValue(ip: *InternPool, ty: Index) Index {
             .type_info,
             => Index.none,
 
-            .unknown => unreachable,
+            .unknown => Index.unknown_unknown,
             .generic_poison => unreachable,
         },
         .int_type => |int_info| {
diff --git a/tests/lsp_features/completion.zig b/tests/lsp_features/completion.zig
index b21dac8a7..d26609e1a 100644
--- a/tests/lsp_features/completion.zig
+++ b/tests/lsp_features/completion.zig
@@ -1867,6 +1867,18 @@ test "tagged union - tag" {
     });
 }
 
+test "tagged union - unknown field type" {
+    try testCompletion(
+        \\const UnknownType: type;
+        \\const U = union(enum) {
+        \\    alpha: UnknownType,
+        \\};
+        \\const foo: U = .<cursor>
+    , &.{
+        .{ .label = "alpha", .kind = .Field },
+    });
+}
+
 test "switch cases" {
     // Because current logic is to list all enums if all else fails,
     // the following tests include an extra enum to ensure that we're not just 'getting lucky'