From e7a6cad087c4142c75683a32b5876c34c5e23647 Mon Sep 17 00:00:00 2001
From: Oleh Prypin <oleh@pryp.in>
Date: Sun, 11 Apr 2021 20:16:23 +0200
Subject: [PATCH 1/3] Auto-deduced type annotations: JSON and YAML

---
 src/big/json.cr                   |  8 ++++----
 src/json/builder.cr               | 26 +++++++++++------------
 src/json/pull_parser.cr           |  4 ++--
 src/json/to_json.cr               | 34 +++++++++++++++----------------
 src/oauth2/access_token/bearer.cr |  2 +-
 src/oauth2/access_token/mac.cr    |  2 +-
 src/uuid/json.cr                  |  2 +-
 src/yaml/any.cr                   |  2 +-
 src/yaml/builder.cr               | 12 +++++------
 src/yaml/nodes/parser.cr          |  8 ++++----
 src/yaml/parser.cr                |  2 +-
 src/yaml/pull_parser.cr           |  2 +-
 src/yaml/schema/core/parser.cr    |  6 +++---
 src/yaml/schema/fail_safe.cr      |  8 ++++----
 14 files changed, 59 insertions(+), 59 deletions(-)

diff --git a/src/big/json.cr b/src/big/json.cr
index c59746bece0f..e07ddcbc3739 100644
--- a/src/big/json.cr
+++ b/src/big/json.cr
@@ -3,7 +3,7 @@ require "big"
 
 class JSON::Builder
   # Writes a big decimal.
-  def number(number : BigDecimal)
+  def number(number : BigDecimal) : IO
     scalar do
       @io << number
     end
@@ -26,7 +26,7 @@ struct BigInt
     to_s
   end
 
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.number(self)
   end
 end
@@ -56,7 +56,7 @@ struct BigFloat
     to_s
   end
 
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.number(self)
   end
 end
@@ -86,7 +86,7 @@ struct BigDecimal
     to_s
   end
 
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.number(self)
   end
 end
diff --git a/src/json/builder.cr b/src/json/builder.cr
index d848d954bc4e..edb91fd89ec8 100644
--- a/src/json/builder.cr
+++ b/src/json/builder.cr
@@ -28,7 +28,7 @@ class JSON::Builder
   end
 
   # Starts a document.
-  def start_document
+  def start_document : JSON::Builder::DocumentStartState
     case state = @state.last
     when StartState
       @state[-1] = DocumentStartState.new
@@ -62,28 +62,28 @@ class JSON::Builder
   end
 
   # Writes a `null` value.
-  def null
+  def null : IO
     scalar do
       @io << "null"
     end
   end
 
   # Writes a boolean value.
-  def bool(value : Bool)
+  def bool(value : Bool) : IO
     scalar do
       @io << value
     end
   end
 
   # Writes an integer.
-  def number(number : Int)
+  def number(number : Int) : IO
     scalar do
       @io << number
     end
   end
 
   # Writes a float.
-  def number(number : Float)
+  def number(number : Float) : IO
     scalar do
       case number
       when .nan?
@@ -100,7 +100,7 @@ class JSON::Builder
   # by invoking `to_s` on it.
   #
   # This method can also be used to write the name of an object field.
-  def string(value)
+  def string(value) : IO
     string = value.to_s
 
     scalar(string: true) do
@@ -157,14 +157,14 @@ class JSON::Builder
   # the IO without processing. This is the only method that
   # might lead to invalid JSON being generated, so you must
   # be sure that *string* contains a valid JSON string.
-  def raw(string : String)
+  def raw(string : String) : IO
     scalar do
       @io << string
     end
   end
 
   # Writes the start of an array.
-  def start_array
+  def start_array : IO
     start_scalar
     increase_indent
     @state.push ArrayState.new(empty: true)
@@ -172,7 +172,7 @@ class JSON::Builder
   end
 
   # Writes the end of an array.
-  def end_array
+  def end_array : JSON::Builder::ArrayState | JSON::Builder::DocumentEndState | JSON::Builder::ObjectState
     case state = @state.last
     when ArrayState
       @state.pop
@@ -193,7 +193,7 @@ class JSON::Builder
   end
 
   # Writes the start of an object.
-  def start_object
+  def start_object : IO
     start_scalar
     increase_indent
     @state.push ObjectState.new(empty: true, name: true)
@@ -201,7 +201,7 @@ class JSON::Builder
   end
 
   # Writes the end of an object.
-  def end_object
+  def end_object : JSON::Builder::ArrayState | JSON::Builder::DocumentEndState | JSON::Builder::ObjectState
     case state = @state.last
     when ObjectState
       unless state.name
@@ -235,12 +235,12 @@ class JSON::Builder
   end
 
   # :ditto:
-  def scalar(value : Int | Float)
+  def scalar(value : Int | Float) : IO
     number(value)
   end
 
   # :ditto:
-  def scalar(value : String)
+  def scalar(value : String) : IO
     string(value)
   end
 
diff --git a/src/json/pull_parser.cr b/src/json/pull_parser.cr
index a4591f98e602..bf4337d7db04 100644
--- a/src/json/pull_parser.cr
+++ b/src/json/pull_parser.cr
@@ -263,7 +263,7 @@ class JSON::PullParser
   # Reads the new value and fill the a JSON builder with it.
   #
   # Use this method with a `JSON::Builder` to read a JSON while building another one.
-  def read_raw(json)
+  def read_raw(json) : IO | JSON::PullParser::Kind
     case @kind
     when .null?
       read_next
@@ -556,7 +556,7 @@ class JSON::PullParser
   #
   # It skips the whole value, not only the next lexer's token.
   # For example if the next value is an array, the whole array will be skipped.
-  def skip
+  def skip : Bool
     @lexer.skip = true
     skip_internal
     @lexer.skip = false
diff --git a/src/json/to_json.cr b/src/json/to_json.cr
index 819a9b02a3f6..0697fd451277 100644
--- a/src/json/to_json.cr
+++ b/src/json/to_json.cr
@@ -25,7 +25,7 @@ class Object
 end
 
 struct Nil
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.null
   end
 
@@ -35,13 +35,13 @@ struct Nil
 end
 
 struct Bool
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.bool(self)
   end
 end
 
 struct Int
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.number(self)
   end
 
@@ -51,7 +51,7 @@ struct Int
 end
 
 struct Float
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.number(self)
   end
 
@@ -61,7 +61,7 @@ struct Float
 end
 
 class String
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.string(self)
   end
 
@@ -71,7 +71,7 @@ class String
 end
 
 struct Path
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     @name.to_json(json)
   end
 
@@ -81,7 +81,7 @@ struct Path
 end
 
 struct Symbol
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.string(to_s)
   end
 
@@ -91,7 +91,7 @@ struct Symbol
 end
 
 class Array
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : Nil
     json.array do
       each &.to_json(json)
     end
@@ -99,7 +99,7 @@ class Array
 end
 
 class Deque
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : Nil
     json.array do
       each &.to_json(json)
     end
@@ -107,7 +107,7 @@ class Deque
 end
 
 struct Set
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : Nil
     json.array do
       each &.to_json(json)
     end
@@ -120,7 +120,7 @@ class Hash
   # Keys are serialized by invoking `to_json_object_key` on them.
   # Values are serialized with the usual `to_json(json : JSON::Builder)`
   # method.
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : Nil
     json.object do
       each do |key, value|
         json.field key.to_json_object_key do
@@ -132,7 +132,7 @@ class Hash
 end
 
 struct Tuple
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.array do
       {% for i in 0...T.size %}
         self[{{i}}].to_json(json)
@@ -154,7 +154,7 @@ struct NamedTuple
 end
 
 struct Time::Format
-  def to_json(value : Time, json : JSON::Builder)
+  def to_json(value : Time, json : JSON::Builder) : IO
     format(value).to_json(json)
   end
 end
@@ -263,7 +263,7 @@ struct Time
   # a time value.
   #
   # See `#from_json` for reference.
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.string(Time::Format::RFC_3339.format(self, fraction_digits: 0))
   end
 end
@@ -343,7 +343,7 @@ end
 # person.to_json    # => %({"birth_date":1459859781})
 # ```
 module Time::EpochConverter
-  def self.to_json(value : Time, json : JSON::Builder)
+  def self.to_json(value : Time, json : JSON::Builder) : IO
     json.number(value.to_unix)
   end
 end
@@ -367,7 +367,7 @@ end
 # timestamp.to_json # => %({"value":1459860483856})
 # ```
 module Time::EpochMillisConverter
-  def self.to_json(value : Time, json : JSON::Builder)
+  def self.to_json(value : Time, json : JSON::Builder) : IO
     json.number(value.to_unix_ms)
   end
 end
@@ -394,7 +394,7 @@ end
 # raw.to_json # => %({"value":123456789876543212345678987654321})
 # ```
 module String::RawConverter
-  def self.to_json(value : String, json : JSON::Builder)
+  def self.to_json(value : String, json : JSON::Builder) : IO
     json.raw(value)
   end
 end
diff --git a/src/oauth2/access_token/bearer.cr b/src/oauth2/access_token/bearer.cr
index d219ce4c4101..efe65cdd0304 100644
--- a/src/oauth2/access_token/bearer.cr
+++ b/src/oauth2/access_token/bearer.cr
@@ -13,7 +13,7 @@ class OAuth2::AccessToken::Bearer < OAuth2::AccessToken
     request.headers["Authorization"] = "Bearer #{access_token}"
   end
 
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO?
     json.object do
       json.field "token_type", "bearer"
       json.field "access_token", access_token
diff --git a/src/oauth2/access_token/mac.cr b/src/oauth2/access_token/mac.cr
index d5152ee873a9..68420b31942f 100644
--- a/src/oauth2/access_token/mac.cr
+++ b/src/oauth2/access_token/mac.cr
@@ -45,7 +45,7 @@ class OAuth2::AccessToken::Mac < OAuth2::AccessToken
     Base64.strict_encode OpenSSL::HMAC.digest(digest, mac_key, normalized_request_string)
   end
 
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.object do
       json.field "token_type", "mac"
       json.field "access_token", access_token
diff --git a/src/uuid/json.cr b/src/uuid/json.cr
index d9b56f7258ca..637c3d6c4f71 100644
--- a/src/uuid/json.cr
+++ b/src/uuid/json.cr
@@ -32,7 +32,7 @@ struct UUID
   # uuid = UUID.new("87b3042b-9b9a-41b7-8b15-a93d3f17025e")
   # uuid.to_json # => "\"87b3042b-9b9a-41b7-8b15-a93d3f17025e\""
   # ```
-  def to_json(json : JSON::Builder)
+  def to_json(json : JSON::Builder) : IO
     json.string(to_s)
   end
 
diff --git a/src/yaml/any.cr b/src/yaml/any.cr
index e037afa2ceb7..385ad43637ea 100644
--- a/src/yaml/any.cr
+++ b/src/yaml/any.cr
@@ -311,7 +311,7 @@ struct YAML::Any
     raw.to_yaml(io)
   end
 
-  def to_json(builder : JSON::Builder)
+  def to_json(builder : JSON::Builder) : IO?
     if (raw = self.raw).is_a?(Slice)
       raise "Can't serialize #{raw.class} to JSON"
     else
diff --git a/src/yaml/builder.cr b/src/yaml/builder.cr
index 77924f184809..ab179190884f 100644
--- a/src/yaml/builder.cr
+++ b/src/yaml/builder.cr
@@ -62,7 +62,7 @@ class YAML::Builder
   end
 
   # Ends a YAML stream.
-  def end_stream
+  def end_stream : IO | Int32 | Nil
     emit stream_end
     @io.flush
   end
@@ -97,14 +97,14 @@ class YAML::Builder
   end
 
   # Starts a sequence.
-  def start_sequence(anchor : String? = nil, tag : String? = nil, style : YAML::SequenceStyle = YAML::SequenceStyle::ANY)
+  def start_sequence(anchor : String? = nil, tag : String? = nil, style : YAML::SequenceStyle = YAML::SequenceStyle::ANY) : Nil
     implicit = tag ? 0 : 1
     emit sequence_start, get_anchor(anchor), string_to_unsafe(tag), implicit, style
     increase_nesting
   end
 
   # Ends a sequence.
-  def end_sequence
+  def end_sequence : Int32
     emit sequence_end
     decrease_nesting
   end
@@ -116,14 +116,14 @@ class YAML::Builder
   end
 
   # Starts a mapping.
-  def start_mapping(anchor : String? = nil, tag : String? = nil, style : YAML::MappingStyle = YAML::MappingStyle::ANY)
+  def start_mapping(anchor : String? = nil, tag : String? = nil, style : YAML::MappingStyle = YAML::MappingStyle::ANY) : Nil
     implicit = tag ? 0 : 1
     emit mapping_start, get_anchor(anchor), string_to_unsafe(tag), implicit, style
     increase_nesting
   end
 
   # Ends a mapping.
-  def end_mapping
+  def end_mapping : Int32
     emit mapping_end
     decrease_nesting
   end
@@ -186,7 +186,7 @@ class YAML::Builder
   end
 
   # Closes the builder, freeing up resources.
-  def close
+  def close : Bool
     finalize
     @closed = true
   end
diff --git a/src/yaml/nodes/parser.cr b/src/yaml/nodes/parser.cr
index 31366cc8bb57..758fc1bb377c 100644
--- a/src/yaml/nodes/parser.cr
+++ b/src/yaml/nodes/parser.cr
@@ -46,7 +46,7 @@ class YAML::Nodes::Parser < YAML::Parser
     node.start_column = @pull_parser.start_column.to_i
   end
 
-  def end_value(node)
+  def end_value(node) : Int32
     node.end_line = @pull_parser.end_line.to_i
     node.end_column = @pull_parser.end_column.to_i
   end
@@ -72,15 +72,15 @@ class YAML::Nodes::Parser < YAML::Parser
     documents << document
   end
 
-  def add_to_document(document, node)
+  def add_to_document(document, node) : Array(YAML::Nodes::Node)
     document << node
   end
 
-  def add_to_sequence(sequence, node)
+  def add_to_sequence(sequence, node) : Array(YAML::Nodes::Node)
     sequence << node
   end
 
-  def add_to_mapping(mapping, key, value)
+  def add_to_mapping(mapping, key, value) : Array(YAML::Nodes::Node)
     mapping[key] = value
   end
 end
diff --git a/src/yaml/parser.cr b/src/yaml/parser.cr
index 308b3fb0af34..1d1ab385514c 100644
--- a/src/yaml/parser.cr
+++ b/src/yaml/parser.cr
@@ -157,7 +157,7 @@ abstract class YAML::Parser
   end
 
   # Closes this parser, freeing up resources.
-  def close
+  def close : Bool
     @pull_parser.close
   end
 
diff --git a/src/yaml/pull_parser.cr b/src/yaml/pull_parser.cr
index d572a7e8f6b1..4115eebe44c9 100644
--- a/src/yaml/pull_parser.cr
+++ b/src/yaml/pull_parser.cr
@@ -321,7 +321,7 @@ class YAML::PullParser
     LibYAML.yaml_event_delete(pointerof(@event))
   end
 
-  def close
+  def close : Bool
     finalize
     @closed = true
   end
diff --git a/src/yaml/schema/core/parser.cr b/src/yaml/schema/core/parser.cr
index ba8629bac067..b5cdb4ccc5a5 100644
--- a/src/yaml/schema/core/parser.cr
+++ b/src/yaml/schema/core/parser.cr
@@ -36,15 +36,15 @@ class YAML::Schema::Core::Parser < YAML::Parser
     Any.new(Core.parse_scalar(@pull_parser))
   end
 
-  def add_to_documents(documents, document)
+  def add_to_documents(documents, document) : Array(YAML::Any)
     documents << document
   end
 
-  def add_to_document(document, node)
+  def add_to_document(document, node) : Array(YAML::Any)
     document.as_a << node
   end
 
-  def add_to_sequence(sequence, node)
+  def add_to_sequence(sequence, node) : Array(YAML::Any)
     sequence.as_a << node
   end
 
diff --git a/src/yaml/schema/fail_safe.cr b/src/yaml/schema/fail_safe.cr
index ec480b2b7108..8edac563fbe3 100644
--- a/src/yaml/schema/fail_safe.cr
+++ b/src/yaml/schema/fail_safe.cr
@@ -50,19 +50,19 @@ module YAML::Schema::FailSafe
       Any.new(@pull_parser.value)
     end
 
-    def add_to_documents(documents, document)
+    def add_to_documents(documents, document) : Array(YAML::Any)
       documents << document
     end
 
-    def add_to_document(document, node)
+    def add_to_document(document, node) : Array(YAML::Any)
       document.as_a << node
     end
 
-    def add_to_sequence(sequence, node)
+    def add_to_sequence(sequence, node) : Array(YAML::Any)
       sequence.as_a << node
     end
 
-    def add_to_mapping(mapping, key, value)
+    def add_to_mapping(mapping, key, value) : YAML::Any
       mapping.as_h[key] = value
     end
   end

From a241dcbec3994029e5c1d57696604c5807cc4a75 Mon Sep 17 00:00:00 2001
From: Oleh Prypin <oleh@pryp.in>
Date: Mon, 12 Apr 2021 01:02:17 +0200
Subject: [PATCH 2/3] Change nonsense return types to Nil: JSON and YAML

---
 src/big/json.cr                   |  8 ++++----
 src/json/builder.cr               | 26 +++++++++++++-------------
 src/json/pull_parser.cr           |  4 ++--
 src/json/to_json.cr               | 26 +++++++++++++-------------
 src/oauth2/access_token/bearer.cr |  2 +-
 src/oauth2/access_token/mac.cr    |  2 +-
 src/uuid/json.cr                  |  2 +-
 src/yaml/any.cr                   |  2 +-
 src/yaml/builder.cr               |  8 ++++----
 src/yaml/nodes/parser.cr          |  8 ++++----
 src/yaml/parser.cr                |  2 +-
 src/yaml/pull_parser.cr           |  2 +-
 src/yaml/schema/core/parser.cr    |  6 +++---
 src/yaml/schema/fail_safe.cr      |  8 ++++----
 14 files changed, 53 insertions(+), 53 deletions(-)

diff --git a/src/big/json.cr b/src/big/json.cr
index e07ddcbc3739..a1f71bb68ee5 100644
--- a/src/big/json.cr
+++ b/src/big/json.cr
@@ -3,7 +3,7 @@ require "big"
 
 class JSON::Builder
   # Writes a big decimal.
-  def number(number : BigDecimal) : IO
+  def number(number : BigDecimal) : Nil
     scalar do
       @io << number
     end
@@ -26,7 +26,7 @@ struct BigInt
     to_s
   end
 
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.number(self)
   end
 end
@@ -56,7 +56,7 @@ struct BigFloat
     to_s
   end
 
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.number(self)
   end
 end
@@ -86,7 +86,7 @@ struct BigDecimal
     to_s
   end
 
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.number(self)
   end
 end
diff --git a/src/json/builder.cr b/src/json/builder.cr
index edb91fd89ec8..04644ef28a7a 100644
--- a/src/json/builder.cr
+++ b/src/json/builder.cr
@@ -28,7 +28,7 @@ class JSON::Builder
   end
 
   # Starts a document.
-  def start_document : JSON::Builder::DocumentStartState
+  def start_document : Nil
     case state = @state.last
     when StartState
       @state[-1] = DocumentStartState.new
@@ -62,28 +62,28 @@ class JSON::Builder
   end
 
   # Writes a `null` value.
-  def null : IO
+  def null : Nil
     scalar do
       @io << "null"
     end
   end
 
   # Writes a boolean value.
-  def bool(value : Bool) : IO
+  def bool(value : Bool) : Nil
     scalar do
       @io << value
     end
   end
 
   # Writes an integer.
-  def number(number : Int) : IO
+  def number(number : Int) : Nil
     scalar do
       @io << number
     end
   end
 
   # Writes a float.
-  def number(number : Float) : IO
+  def number(number : Float) : Nil
     scalar do
       case number
       when .nan?
@@ -100,7 +100,7 @@ class JSON::Builder
   # by invoking `to_s` on it.
   #
   # This method can also be used to write the name of an object field.
-  def string(value) : IO
+  def string(value) : Nil
     string = value.to_s
 
     scalar(string: true) do
@@ -157,14 +157,14 @@ class JSON::Builder
   # the IO without processing. This is the only method that
   # might lead to invalid JSON being generated, so you must
   # be sure that *string* contains a valid JSON string.
-  def raw(string : String) : IO
+  def raw(string : String) : Nil
     scalar do
       @io << string
     end
   end
 
   # Writes the start of an array.
-  def start_array : IO
+  def start_array : Nil
     start_scalar
     increase_indent
     @state.push ArrayState.new(empty: true)
@@ -172,7 +172,7 @@ class JSON::Builder
   end
 
   # Writes the end of an array.
-  def end_array : JSON::Builder::ArrayState | JSON::Builder::DocumentEndState | JSON::Builder::ObjectState
+  def end_array : Nil
     case state = @state.last
     when ArrayState
       @state.pop
@@ -193,7 +193,7 @@ class JSON::Builder
   end
 
   # Writes the start of an object.
-  def start_object : IO
+  def start_object : Nil
     start_scalar
     increase_indent
     @state.push ObjectState.new(empty: true, name: true)
@@ -201,7 +201,7 @@ class JSON::Builder
   end
 
   # Writes the end of an object.
-  def end_object : JSON::Builder::ArrayState | JSON::Builder::DocumentEndState | JSON::Builder::ObjectState
+  def end_object : Nil
     case state = @state.last
     when ObjectState
       unless state.name
@@ -235,12 +235,12 @@ class JSON::Builder
   end
 
   # :ditto:
-  def scalar(value : Int | Float) : IO
+  def scalar(value : Int | Float) : Nil
     number(value)
   end
 
   # :ditto:
-  def scalar(value : String) : IO
+  def scalar(value : String) : Nil
     string(value)
   end
 
diff --git a/src/json/pull_parser.cr b/src/json/pull_parser.cr
index bf4337d7db04..82edd541ca89 100644
--- a/src/json/pull_parser.cr
+++ b/src/json/pull_parser.cr
@@ -263,7 +263,7 @@ class JSON::PullParser
   # Reads the new value and fill the a JSON builder with it.
   #
   # Use this method with a `JSON::Builder` to read a JSON while building another one.
-  def read_raw(json) : IO | JSON::PullParser::Kind
+  def read_raw(json) : Nil
     case @kind
     when .null?
       read_next
@@ -556,7 +556,7 @@ class JSON::PullParser
   #
   # It skips the whole value, not only the next lexer's token.
   # For example if the next value is an array, the whole array will be skipped.
-  def skip : Bool
+  def skip : Nil
     @lexer.skip = true
     skip_internal
     @lexer.skip = false
diff --git a/src/json/to_json.cr b/src/json/to_json.cr
index 0697fd451277..b77dc7bb63d3 100644
--- a/src/json/to_json.cr
+++ b/src/json/to_json.cr
@@ -25,7 +25,7 @@ class Object
 end
 
 struct Nil
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.null
   end
 
@@ -35,13 +35,13 @@ struct Nil
 end
 
 struct Bool
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.bool(self)
   end
 end
 
 struct Int
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.number(self)
   end
 
@@ -51,7 +51,7 @@ struct Int
 end
 
 struct Float
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.number(self)
   end
 
@@ -61,7 +61,7 @@ struct Float
 end
 
 class String
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.string(self)
   end
 
@@ -71,7 +71,7 @@ class String
 end
 
 struct Path
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     @name.to_json(json)
   end
 
@@ -81,7 +81,7 @@ struct Path
 end
 
 struct Symbol
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.string(to_s)
   end
 
@@ -132,7 +132,7 @@ class Hash
 end
 
 struct Tuple
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.array do
       {% for i in 0...T.size %}
         self[{{i}}].to_json(json)
@@ -154,7 +154,7 @@ struct NamedTuple
 end
 
 struct Time::Format
-  def to_json(value : Time, json : JSON::Builder) : IO
+  def to_json(value : Time, json : JSON::Builder) : Nil
     format(value).to_json(json)
   end
 end
@@ -263,7 +263,7 @@ struct Time
   # a time value.
   #
   # See `#from_json` for reference.
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.string(Time::Format::RFC_3339.format(self, fraction_digits: 0))
   end
 end
@@ -343,7 +343,7 @@ end
 # person.to_json    # => %({"birth_date":1459859781})
 # ```
 module Time::EpochConverter
-  def self.to_json(value : Time, json : JSON::Builder) : IO
+  def self.to_json(value : Time, json : JSON::Builder) : Nil
     json.number(value.to_unix)
   end
 end
@@ -367,7 +367,7 @@ end
 # timestamp.to_json # => %({"value":1459860483856})
 # ```
 module Time::EpochMillisConverter
-  def self.to_json(value : Time, json : JSON::Builder) : IO
+  def self.to_json(value : Time, json : JSON::Builder) : Nil
     json.number(value.to_unix_ms)
   end
 end
@@ -394,7 +394,7 @@ end
 # raw.to_json # => %({"value":123456789876543212345678987654321})
 # ```
 module String::RawConverter
-  def self.to_json(value : String, json : JSON::Builder) : IO
+  def self.to_json(value : String, json : JSON::Builder) : Nil
     json.raw(value)
   end
 end
diff --git a/src/oauth2/access_token/bearer.cr b/src/oauth2/access_token/bearer.cr
index efe65cdd0304..9bd6d0572045 100644
--- a/src/oauth2/access_token/bearer.cr
+++ b/src/oauth2/access_token/bearer.cr
@@ -13,7 +13,7 @@ class OAuth2::AccessToken::Bearer < OAuth2::AccessToken
     request.headers["Authorization"] = "Bearer #{access_token}"
   end
 
-  def to_json(json : JSON::Builder) : IO?
+  def to_json(json : JSON::Builder) : Nil
     json.object do
       json.field "token_type", "bearer"
       json.field "access_token", access_token
diff --git a/src/oauth2/access_token/mac.cr b/src/oauth2/access_token/mac.cr
index 68420b31942f..9ba4dfe3f52b 100644
--- a/src/oauth2/access_token/mac.cr
+++ b/src/oauth2/access_token/mac.cr
@@ -45,7 +45,7 @@ class OAuth2::AccessToken::Mac < OAuth2::AccessToken
     Base64.strict_encode OpenSSL::HMAC.digest(digest, mac_key, normalized_request_string)
   end
 
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.object do
       json.field "token_type", "mac"
       json.field "access_token", access_token
diff --git a/src/uuid/json.cr b/src/uuid/json.cr
index 637c3d6c4f71..040668f4a6b8 100644
--- a/src/uuid/json.cr
+++ b/src/uuid/json.cr
@@ -32,7 +32,7 @@ struct UUID
   # uuid = UUID.new("87b3042b-9b9a-41b7-8b15-a93d3f17025e")
   # uuid.to_json # => "\"87b3042b-9b9a-41b7-8b15-a93d3f17025e\""
   # ```
-  def to_json(json : JSON::Builder) : IO
+  def to_json(json : JSON::Builder) : Nil
     json.string(to_s)
   end
 
diff --git a/src/yaml/any.cr b/src/yaml/any.cr
index 385ad43637ea..bc8d95bf385a 100644
--- a/src/yaml/any.cr
+++ b/src/yaml/any.cr
@@ -311,7 +311,7 @@ struct YAML::Any
     raw.to_yaml(io)
   end
 
-  def to_json(builder : JSON::Builder) : IO?
+  def to_json(builder : JSON::Builder) : Nil
     if (raw = self.raw).is_a?(Slice)
       raise "Can't serialize #{raw.class} to JSON"
     else
diff --git a/src/yaml/builder.cr b/src/yaml/builder.cr
index ab179190884f..ddc2c2244353 100644
--- a/src/yaml/builder.cr
+++ b/src/yaml/builder.cr
@@ -62,7 +62,7 @@ class YAML::Builder
   end
 
   # Ends a YAML stream.
-  def end_stream : IO | Int32 | Nil
+  def end_stream : Nil
     emit stream_end
     @io.flush
   end
@@ -104,7 +104,7 @@ class YAML::Builder
   end
 
   # Ends a sequence.
-  def end_sequence : Int32
+  def end_sequence : Nil
     emit sequence_end
     decrease_nesting
   end
@@ -123,7 +123,7 @@ class YAML::Builder
   end
 
   # Ends a mapping.
-  def end_mapping : Int32
+  def end_mapping : Nil
     emit mapping_end
     decrease_nesting
   end
@@ -186,7 +186,7 @@ class YAML::Builder
   end
 
   # Closes the builder, freeing up resources.
-  def close : Bool
+  def close : Nil
     finalize
     @closed = true
   end
diff --git a/src/yaml/nodes/parser.cr b/src/yaml/nodes/parser.cr
index 758fc1bb377c..8f44c292a507 100644
--- a/src/yaml/nodes/parser.cr
+++ b/src/yaml/nodes/parser.cr
@@ -46,7 +46,7 @@ class YAML::Nodes::Parser < YAML::Parser
     node.start_column = @pull_parser.start_column.to_i
   end
 
-  def end_value(node) : Int32
+  def end_value(node) : Nil
     node.end_line = @pull_parser.end_line.to_i
     node.end_column = @pull_parser.end_column.to_i
   end
@@ -72,15 +72,15 @@ class YAML::Nodes::Parser < YAML::Parser
     documents << document
   end
 
-  def add_to_document(document, node) : Array(YAML::Nodes::Node)
+  def add_to_document(document, node) : Nil
     document << node
   end
 
-  def add_to_sequence(sequence, node) : Array(YAML::Nodes::Node)
+  def add_to_sequence(sequence, node) : Nil
     sequence << node
   end
 
-  def add_to_mapping(mapping, key, value) : Array(YAML::Nodes::Node)
+  def add_to_mapping(mapping, key, value) : Nil
     mapping[key] = value
   end
 end
diff --git a/src/yaml/parser.cr b/src/yaml/parser.cr
index 1d1ab385514c..1a81b5e7ad34 100644
--- a/src/yaml/parser.cr
+++ b/src/yaml/parser.cr
@@ -157,7 +157,7 @@ abstract class YAML::Parser
   end
 
   # Closes this parser, freeing up resources.
-  def close : Bool
+  def close : Nil
     @pull_parser.close
   end
 
diff --git a/src/yaml/pull_parser.cr b/src/yaml/pull_parser.cr
index 4115eebe44c9..ba23cbb5239d 100644
--- a/src/yaml/pull_parser.cr
+++ b/src/yaml/pull_parser.cr
@@ -321,7 +321,7 @@ class YAML::PullParser
     LibYAML.yaml_event_delete(pointerof(@event))
   end
 
-  def close : Bool
+  def close : Nil
     finalize
     @closed = true
   end
diff --git a/src/yaml/schema/core/parser.cr b/src/yaml/schema/core/parser.cr
index b5cdb4ccc5a5..8ff23d0157b3 100644
--- a/src/yaml/schema/core/parser.cr
+++ b/src/yaml/schema/core/parser.cr
@@ -36,15 +36,15 @@ class YAML::Schema::Core::Parser < YAML::Parser
     Any.new(Core.parse_scalar(@pull_parser))
   end
 
-  def add_to_documents(documents, document) : Array(YAML::Any)
+  def add_to_documents(documents, document) : Nil
     documents << document
   end
 
-  def add_to_document(document, node) : Array(YAML::Any)
+  def add_to_document(document, node) : Nil
     document.as_a << node
   end
 
-  def add_to_sequence(sequence, node) : Array(YAML::Any)
+  def add_to_sequence(sequence, node) : Nil
     sequence.as_a << node
   end
 
diff --git a/src/yaml/schema/fail_safe.cr b/src/yaml/schema/fail_safe.cr
index 8edac563fbe3..3a88e56b78fd 100644
--- a/src/yaml/schema/fail_safe.cr
+++ b/src/yaml/schema/fail_safe.cr
@@ -50,19 +50,19 @@ module YAML::Schema::FailSafe
       Any.new(@pull_parser.value)
     end
 
-    def add_to_documents(documents, document) : Array(YAML::Any)
+    def add_to_documents(documents, document) : Nil
       documents << document
     end
 
-    def add_to_document(document, node) : Array(YAML::Any)
+    def add_to_document(document, node) : Nil
       document.as_a << node
     end
 
-    def add_to_sequence(sequence, node) : Array(YAML::Any)
+    def add_to_sequence(sequence, node) : Nil
       sequence.as_a << node
     end
 
-    def add_to_mapping(mapping, key, value) : YAML::Any
+    def add_to_mapping(mapping, key, value) : Nil
       mapping.as_h[key] = value
     end
   end

From 913ce5823c1c837a21cb78a9ea9552d82e55cca1 Mon Sep 17 00:00:00 2001
From: Oleh Prypin <oleh@pryp.in>
Date: Mon, 12 Apr 2021 21:25:20 +0200
Subject: [PATCH 3/3] Fix a bug relying on truthiness of JSON::Builder#string

---
 src/compiler/crystal/tools/doc/type.cr | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/crystal/tools/doc/type.cr b/src/compiler/crystal/tools/doc/type.cr
index 2db6db348050..a212ac1b8d07 100644
--- a/src/compiler/crystal/tools/doc/type.cr
+++ b/src/compiler/crystal/tools/doc/type.cr
@@ -760,7 +760,7 @@ class Crystal::Doc::Type
       builder.field "full_name", full_name
       builder.field "name", name
       builder.field "abstract", abstract?
-      builder.field "superclass" { superclass.try(&.to_json_simple(builder)) || builder.scalar(nil) }
+      builder.field "superclass" { (s = superclass) ? s.to_json_simple(builder) : builder.null }
       builder.field "ancestors" do
         builder.array do
           ancestors.each &.to_json_simple(builder)
@@ -795,7 +795,7 @@ class Crystal::Doc::Type
           including_types.each &.to_json_simple(builder)
         end
       end
-      builder.field "namespace" { namespace.try(&.to_json_simple(builder)) || builder.scalar(nil) }
+      builder.field "namespace" { (n = namespace) ? n.to_json_simple(builder) : builder.null }
       builder.field "doc", doc
       builder.field "summary", formatted_summary
       builder.field "class_methods", class_methods