From cb7faca3ee9129a62d562e74bc178bbadf964c90 Mon Sep 17 00:00:00 2001
From: Christopher Hertel <mail@christopher-hertel.de>
Date: Mon, 2 Nov 2026 22:52:38 +0100
Subject: [PATCH] [Server] Fix `"0"` prefix offering all completions

`empty("0")` is true, so `EnumCompletionProvider` and `ListCompletionProvider`
returned every value for that prefix.
---
 CHANGELOG.md                                          |  1 +
 src/Capability/Completion/EnumCompletionProvider.php  |  2 +-
 src/Capability/Completion/ListCompletionProvider.php  |  2 +-
 .../Completion/EnumCompletionProviderTest.php         | 11 +++++++++--
 .../Completion/ListCompletionProviderTest.php         |  7 +++++++
 5 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 69c8beb09..74954a863 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * Fix `InMemorySessionStore::exists()` reporting a session past its TTL as existing, while `read()` already treated it as gone.
 * Fix `Psr16NotificationBus` subscribers missing the notifications published after the bus stayed quiet for longer than its TTL: the sequence counter no longer expires, and a subscriber whose cursor is ahead of a lost counter reads what the bus holds.
 * Fix `Session::save()` wiping the other keys of a session that the store failed to read, e.g. when `Psr16SessionStore` hits a cache error: it now returns `false` instead of writing the changed keys alone.
+* Fix `EnumCompletionProvider` and `ListCompletionProvider` offering all values for the prefix `"0"` instead of only the values that start with it.
 * Add `Psr6SessionStore` and `Psr6NotificationBus`, which work like `Psr16SessionStore` and `Psr16NotificationBus` over a PSR-6 cache pool. `Builder::setDiscovery()` also accepts a PSR-6 pool as `$cache`.
 
 ### Client
diff --git a/src/Capability/Completion/EnumCompletionProvider.php b/src/Capability/Completion/EnumCompletionProvider.php
index 3c50eba56..f98161932 100644
--- a/src/Capability/Completion/EnumCompletionProvider.php
+++ b/src/Capability/Completion/EnumCompletionProvider.php
@@ -40,7 +40,7 @@ public function __construct(string $enumClass)
 
     public function getCompletions(string $currentValue): array
     {
-        if (empty($currentValue)) {
+        if ('' === $currentValue) {
             return $this->values;
         }
 
diff --git a/src/Capability/Completion/ListCompletionProvider.php b/src/Capability/Completion/ListCompletionProvider.php
index 45a41c45b..5e066dec9 100644
--- a/src/Capability/Completion/ListCompletionProvider.php
+++ b/src/Capability/Completion/ListCompletionProvider.php
@@ -31,7 +31,7 @@ public function __construct(array $values)
 
     public function getCompletions(string $currentValue): array
     {
-        if (empty($currentValue)) {
+        if ('' === $currentValue) {
             return $this->values;
         }
 
diff --git a/tests/Unit/Capability/Completion/EnumCompletionProviderTest.php b/tests/Unit/Capability/Completion/EnumCompletionProviderTest.php
index f0ca3d46b..4bbc292ad 100644
--- a/tests/Unit/Capability/Completion/EnumCompletionProviderTest.php
+++ b/tests/Unit/Capability/Completion/EnumCompletionProviderTest.php
@@ -32,10 +32,17 @@ public function testPrefixMatchesKeepCaseOrder(): void
         $this->assertSame([], $provider->getCompletions('missing'));
     }
 
-    public function testZeroPrefixOffersAllCases(): void
+    public function testEmptyPrefixOffersAllCases(): void
     {
         $provider = new EnumCompletionProvider(CompletionFixture::class);
 
-        $this->assertSame(['alpha', 'alpine', 'algebra', '0'], $provider->getCompletions('0'));
+        $this->assertSame(['alpha', 'alpine', 'algebra', '0'], $provider->getCompletions(''));
+    }
+
+    public function testZeroIsMatchedAsPrefix(): void
+    {
+        $provider = new EnumCompletionProvider(CompletionFixture::class);
+
+        $this->assertSame(['0'], $provider->getCompletions('0'));
     }
 }
diff --git a/tests/Unit/Capability/Completion/ListCompletionProviderTest.php b/tests/Unit/Capability/Completion/ListCompletionProviderTest.php
index 9a9ca9fc9..4870d7373 100644
--- a/tests/Unit/Capability/Completion/ListCompletionProviderTest.php
+++ b/tests/Unit/Capability/Completion/ListCompletionProviderTest.php
@@ -42,6 +42,13 @@ public function testNumericValuesBecomeStrings(): void
         $this->assertSame(['101', '102.5'], $provider->getCompletions('10'));
     }
 
+    public function testZeroIsMatchedAsPrefix(): void
+    {
+        $provider = new ListCompletionProvider(['zero', '0', '01']);
+
+        $this->assertSame(['0', '01'], $provider->getCompletions('0'));
+    }
+
     public function testKeysAreDiscarded(): void
     {
         $provider = new ListCompletionProvider([5 => 'a', 9 => 'b']);