From ef392525cce91fa7960eb33bb5183d4fb9a70dab Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20M=C3=BCller?= <straightshoota@gmail.com>
Date: Mon, 17 Apr 2023 18:14:14 +0200
Subject: [PATCH 1/3] Refactor `String` header layout reflection

---
 src/string.cr         | 19 +++++++++++++++----
 src/string/builder.cr |  7 ++++---
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/src/string.cr b/src/string.cr
index 9454f6d1ea03..7a11c6a09045 100644
--- a/src/string.cr
+++ b/src/string.cr
@@ -146,7 +146,9 @@ class String
   TYPE_ID = "".crystal_type_id
 
   # :nodoc:
-  HEADER_SIZE = sizeof({Int32, Int32, Int32})
+  #
+  # Holds the offset to the first character byte.
+  HEADER_SIZE = offsetof(String, @c)
 
   include Comparable(self)
 
@@ -266,9 +268,18 @@ class String
       str = GC.realloc(str, bytesize.to_u32 + HEADER_SIZE + 1)
     end
 
-    str_header = str.as({Int32, Int32, Int32}*)
-    str_header.value = {TYPE_ID, bytesize.to_i, size.to_i}
-    str.as(String)
+    str.as(Pointer(typeof(TYPE_ID))).value = TYPE_ID
+    str = str.as(String)
+    str.initialize_header(bytesize.to_i, size.to_i)
+    str
+  end
+
+  # :nodoc:
+  #
+  # Initializes the header information of a `String` instance.
+  # The actual character content at `@c` is expected to be already filled and is
+  # unaffected by this method.
+  def initialize_header(@bytesize : Int32, @length : Int32 = 0)
   end
 
   # Builds a `String` by creating a `String::Builder` with the given initial capacity, yielding
diff --git a/src/string/builder.cr b/src/string/builder.cr
index d1add8dc9be2..89e8ffbd3055 100644
--- a/src/string/builder.cr
+++ b/src/string/builder.cr
@@ -117,9 +117,10 @@ class String::Builder < IO
       resize_to_capacity(real_bytesize)
     end
 
-    header = @buffer.as({Int32, Int32, Int32}*)
-    header.value = {String::TYPE_ID, @bytesize - 1, 0}
-    @buffer.as(String)
+    @buffer.as(Pointer(typeof(String::TYPE_ID))).value = String::TYPE_ID
+    str = @buffer.as(String)
+    str.initialize_header((bytesize - 1).to_i)
+    str
   end
 
   private def real_bytesize

From 9199b60c0ccd3cf5f6db18183303b75ea3295e05 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20M=C3=BCller?= <straightshoota@gmail.com>
Date: Mon, 17 Apr 2023 21:44:00 +0200
Subject: [PATCH 2/3] Remove unnecesary and harmful bounds check

---
 src/string/builder.cr | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/string/builder.cr b/src/string/builder.cr
index 89e8ffbd3055..b34cdf97d923 100644
--- a/src/string/builder.cr
+++ b/src/string/builder.cr
@@ -14,7 +14,6 @@ class String::Builder < IO
     # Make sure to also be able to hold
     # the header size plus the trailing zero byte
     capacity += String::HEADER_SIZE + 1
-    String.check_capacity_in_bounds(capacity)
 
     @buffer = GC.malloc_atomic(capacity.to_u32).as(UInt8*)
     @bytesize = 0

From 5789771b1ba3c3227419e3abb4da6cfdfabf0ea1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20M=C3=BCller?= <straightshoota@gmail.com>
Date: Tue, 18 Apr 2023 12:27:41 +0200
Subject: [PATCH 3/3] Use `set_crystal_type_id` and remove `String::TYPE_ID`

---
 src/string.cr         | 5 +----
 src/string/builder.cr | 2 +-
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/string.cr b/src/string.cr
index 7a11c6a09045..61237013800f 100644
--- a/src/string.cr
+++ b/src/string.cr
@@ -142,9 +142,6 @@ require "c/string"
 # behavior on invalid strings. If this is undesired, `#scrub` could be used to
 # remove the offending byte sequences first.
 class String
-  # :nodoc:
-  TYPE_ID = "".crystal_type_id
-
   # :nodoc:
   #
   # Holds the offset to the first character byte.
@@ -268,7 +265,7 @@ class String
       str = GC.realloc(str, bytesize.to_u32 + HEADER_SIZE + 1)
     end
 
-    str.as(Pointer(typeof(TYPE_ID))).value = TYPE_ID
+    set_crystal_type_id(str)
     str = str.as(String)
     str.initialize_header(bytesize.to_i, size.to_i)
     str
diff --git a/src/string/builder.cr b/src/string/builder.cr
index b34cdf97d923..0fb77f4ca41b 100644
--- a/src/string/builder.cr
+++ b/src/string/builder.cr
@@ -116,7 +116,7 @@ class String::Builder < IO
       resize_to_capacity(real_bytesize)
     end
 
-    @buffer.as(Pointer(typeof(String::TYPE_ID))).value = String::TYPE_ID
+    String.set_crystal_type_id(@buffer)
     str = @buffer.as(String)
     str.initialize_header((bytesize - 1).to_i)
     str