From 91f5d4f3e3a0440a5d032df8c3ca29743e6c3b67 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?M=C3=A1t=C3=A9=20Szab=C3=B3?= <mszabo@slack-corp.com>
Date: Fri, 24 Apr 2026 20:42:49 +0200
Subject: [PATCH] Fix type resolution for fully-qualified type hints with
 leading backslash

Fully-qualified types like `\HH\Awaitable<_>` were not matching known
type patterns in `get_type_from_hint` because the leading `\` was not
stripped before the match. This caused them to fall through to
`TReference` -> `TNamedObject` instead of the correct `TAwaitable`,
making them incompatible with parameter types resolved from stubs.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>
---
 src/code_info_builder/typehint_resolver.rs          |  7 +++++--
 .../FunctionCall/aliasedArgumentType/input.hack     | 13 +++++++++++++
 .../FunctionCall/aliasedArgumentType/output.txt     |  1 +
 3 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 tests/inference/FunctionCall/aliasedArgumentType/input.hack
 create mode 100644 tests/inference/FunctionCall/aliasedArgumentType/output.txt

diff --git a/src/code_info_builder/typehint_resolver.rs b/src/code_info_builder/typehint_resolver.rs
index 68a21086..d43d7651 100644
--- a/src/code_info_builder/typehint_resolver.rs
+++ b/src/code_info_builder/typehint_resolver.rs
@@ -510,6 +510,9 @@ pub fn get_type_from_hint(
     let base = match hint {
         Hint_::Happly(id, extra_info) => {
             let applied_type = &id.1;
+            let applied_type_str = applied_type
+                .strip_prefix('\\')
+                .unwrap_or(applied_type.as_str());
 
             if let Some(resolved_name) = resolved_names.get(&(id.0.start_offset() as u32)) {
                 if let Some((_, type_name)) = type_context
@@ -521,7 +524,7 @@ pub fn get_type_from_hint(
                 }
             }
 
-            match applied_type.as_str() {
+            match applied_type_str {
                 "int" => TAtomic::TInt,
                 "string" => TAtomic::TString,
                 "arraykey" => TAtomic::TArraykey { from_any: false },
@@ -664,7 +667,7 @@ pub fn get_type_from_hint(
                 }
                 "resource" => TAtomic::TResource,
                 "_" => TAtomic::TPlaceholder,
-                "HH\\FIXME\\MISSING_RETURN_TYPE" | "\\HH\\FIXME\\MISSING_RETURN_TYPE" => {
+                "HH\\FIXME\\MISSING_RETURN_TYPE" => {
                     return None;
                 }
                 _ => get_reference_type(
diff --git a/tests/inference/FunctionCall/aliasedArgumentType/input.hack b/tests/inference/FunctionCall/aliasedArgumentType/input.hack
new file mode 100644
index 00000000..b09cf401
--- /dev/null
+++ b/tests/inference/FunctionCall/aliasedArgumentType/input.hack
@@ -0,0 +1,13 @@
+namespace A;
+
+function foo(mixed $test): void {
+    if ($test is \HH\Awaitable<_>) {
+        \HH\Asio\join($test);
+    }
+}
+
+function bar(mixed $test): void {
+    if ($test is Awaitable<_>) {
+        Asio\join($test);
+    }
+}
diff --git a/tests/inference/FunctionCall/aliasedArgumentType/output.txt b/tests/inference/FunctionCall/aliasedArgumentType/output.txt
new file mode 100644
index 00000000..8b137891
--- /dev/null
+++ b/tests/inference/FunctionCall/aliasedArgumentType/output.txt
@@ -0,0 +1 @@
+