From 64aac345d38f98520c367c080829f06fd47472b6 Mon Sep 17 00:00:00 2001
From: Andrew Kaster <akaster@serenityos.org>
Date: Sat, 17 Jul 2021 16:27:12 -0600
Subject: [PATCH] AK: Use new Formatter for each element in
 Formatter<Vector<T>>

The state of the formatter for the previous element should be thrown
away for each iteration. This showed up when trying to format a
Vector<String>, since Formatter<StringView> was unhappy about some state
that gets set when it's called. Add a test for Formatter<Vector>.
---
 AK/Format.h             |  4 +++-
 Tests/AK/TestFormat.cpp | 17 +++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/AK/Format.h b/AK/Format.h
index 199cab97b4..8c9f3184d1 100644
--- a/AK/Format.h
+++ b/AK/Format.h
@@ -354,8 +354,10 @@ requires(HasFormatter<T>) struct Formatter<Vector<T>> : StandardFormatter {
         builder.put_literal("[ "sv);
         bool first = true;
         for (auto& content : value) {
-            if (!first)
+            if (!first) {
                 builder.put_literal(", "sv);
+                content_fmt = Formatter<T> {};
+            }
             first = false;
             content_fmt.format(builder, content);
         }
diff --git a/Tests/AK/TestFormat.cpp b/Tests/AK/TestFormat.cpp
index 3c61179879..28696cce28 100644
--- a/Tests/AK/TestFormat.cpp
+++ b/Tests/AK/TestFormat.cpp
@@ -8,6 +8,7 @@
 
 #include <AK/String.h>
 #include <AK/StringBuilder.h>
+#include <AK/Vector.h>
 
 TEST_CASE(is_integral_works_properly)
 {
@@ -306,3 +307,19 @@ TEST_CASE(hex_dump)
     EXPECT_EQ(String::formatted("{:>2hex-dump}", "0000"), "3030    00\n3030    00");
     EXPECT_EQ(String::formatted("{:*>4hex-dump}", "0000"), "30303030****0000");
 }
+
+TEST_CASE(vector_format)
+{
+    {
+        Vector<int> v { 1, 2, 3, 4 };
+        EXPECT_EQ(String::formatted("{}", v), "[ 1, 2, 3, 4 ]");
+    }
+    {
+        Vector<StringView> v { "1"sv, "2"sv, "3"sv, "4"sv };
+        EXPECT_EQ(String::formatted("{}", v), "[ 1, 2, 3, 4 ]");
+    }
+    {
+        Vector<Vector<String>> v { { "1"sv, "2"sv }, { "3"sv, "4"sv } };
+        EXPECT_EQ(String::formatted("{}", v), "[ [ 1, 2 ], [ 3, 4 ] ]");
+    }
+}