Add return type restrictions to methods related to String (#10583)

src/char.cr

@@ -61,7 +61,7 @@ struct Char
   # 'b' - 'a' # => 1
   # 'c' - 'a' # => 2
   # ```
-  def -(other : Char)
+  def -(other : Char) : Int32
     ord - other.ord
   end
 
@@ -70,7 +70,7 @@ struct Char
   # ```
   # 'f' + "oo" # => "foo"
   # ```
-  def +(str : String)
+  def +(str : String) : String
     bytesize = str.bytesize + self.bytesize
     String.new(bytesize) do |buffer|
       count = 0
@@ -142,7 +142,7 @@ struct Char
 
   # Returns `true` if this char is an ASCII character
   # (codepoint is in (0..127))
-  def ascii?
+  def ascii? : Bool
     ord < 128
   end
 
@@ -155,7 +155,7 @@ struct Char
   # 'z'.ascii_number?     # => false
   # 'z'.ascii_number?(36) # => true
   # ```
-  def ascii_number?(base : Int = 10)
+  def ascii_number?(base : Int = 10) : Bool
     !!to_i?(base)
   end
 
@@ -165,7 +165,7 @@ struct Char
   # '1'.number? # => true
   # 'a'.number? # => false
   # ```
-  def number?
+  def number? : Bool
     ascii? ? ascii_number? : Unicode.number?(self)
   end
 
@@ -177,7 +177,7 @@ struct Char
   # 'G'.ascii_lowercase? # => false
   # '.'.ascii_lowercase? # => false
   # ```
-  def ascii_lowercase?
+  def ascii_lowercase? : Bool
     'a' <= self <= 'z'
   end
 
@@ -189,7 +189,7 @@ struct Char
   # 'G'.lowercase? # => false
   # '.'.lowercase? # => false
   # ```
-  def lowercase?
+  def lowercase? : Bool
     ascii? ? ascii_lowercase? : Unicode.lowercase?(self)
   end
 
@@ -201,7 +201,7 @@ struct Char
   # 'c'.ascii_uppercase? # => false
   # '.'.ascii_uppercase? # => false
   # ```
-  def ascii_uppercase?
+  def ascii_uppercase? : Bool
     'A' <= self <= 'Z'
   end
 
@@ -213,7 +213,7 @@ struct Char
   # 'c'.uppercase? # => false
   # '.'.uppercase? # => false
   # ```
-  def uppercase?
+  def uppercase? : Bool
     ascii? ? ascii_uppercase? : Unicode.uppercase?(self)
   end
 
@@ -224,7 +224,7 @@ struct Char
   # 'á'.ascii_letter? # => false
   # '8'.ascii_letter? # => false
   # ```
-  def ascii_letter?
+  def ascii_letter? : Bool
     ascii_lowercase? || ascii_uppercase?
   end
 
@@ -235,7 +235,7 @@ struct Char
   # 'á'.letter? # => true
   # '8'.letter? # => false
   # ```
-  def letter?
+  def letter? : Bool
     ascii? ? ascii_letter? : Unicode.letter?(self)
   end
 
@@ -246,7 +246,7 @@ struct Char
   # '8'.ascii_alphanumeric? # => true
   # '.'.ascii_alphanumeric? # => false
   # ```
-  def ascii_alphanumeric?
+  def ascii_alphanumeric? : Bool
     ascii_letter? || ascii_number?
   end
 
@@ -257,7 +257,7 @@ struct Char
   # '8'.alphanumeric? # => true
   # '.'.alphanumeric? # => false
   # ```
-  def alphanumeric?
+  def alphanumeric? : Bool
     letter? || number?
   end
 
@@ -268,7 +268,7 @@ struct Char
   # '\t'.ascii_whitespace? # => true
   # 'b'.ascii_whitespace?  # => false
   # ```
-  def ascii_whitespace?
+  def ascii_whitespace? : Bool
     self == ' ' || 9 <= ord <= 13
   end
 
@@ -279,7 +279,7 @@ struct Char
   # '\t'.whitespace? # => true
   # 'b'.whitespace?  # => false
   # ```
-  def whitespace?
+  def whitespace? : Bool
     ascii? ? ascii_whitespace? : Unicode.whitespace?(self)
   end
 
@@ -291,7 +291,7 @@ struct Char
   # 'F'.hex? # => true
   # 'g'.hex? # => false
   # ```
-  def hex?
+  def hex? : Bool
     ascii_number? 16
   end
 
@@ -322,7 +322,7 @@ struct Char
   # '\\'.in_set? "\\A"   # => false
   # '\\'.in_set? "X-\\w" # => true
   # ```
-  def in_set?(*sets : String)
+  def in_set?(*sets : String) : Bool
     if sets.size > 1
       return sets.all? { |set| in_set?(set) }
     end
@@ -388,7 +388,7 @@ struct Char
   # 'x'.downcase # => 'x'
   # '.'.downcase # => '.'
   # ```
-  def downcase(options = Unicode::CaseOptions::None)
+  def downcase(options = Unicode::CaseOptions::None) : Char
     Unicode.downcase(self, options)
   end
 
@@ -415,7 +415,7 @@ struct Char
   # 'X'.upcase # => 'X'
   # '.'.upcase # => '.'
   # ```
-  def upcase(options = Unicode::CaseOptions::None)
+  def upcase(options = Unicode::CaseOptions::None) : Char
     Unicode.upcase(self, options)
   end
 
@@ -446,7 +446,7 @@ struct Char
   # ```
   #
   # This method allows creating a `Range` of chars.
-  def succ
+  def succ : Char
     (ord + 1).chr
   end
 
@@ -456,7 +456,7 @@ struct Char
   # 'b'.pred # => 'a'
   # 'ぃ'.pred # => 'あ'
   # ```
-  def pred
+  def pred : Char
     (ord - 1).chr
   end
 
@@ -471,17 +471,17 @@ struct Char
   #   char.control? # => true
   # end
   # ```
-  def ascii_control?
+  def ascii_control? : Bool
     ord < 0x20 || (0x7F <= ord <= 0x9F)
   end
 
   # Returns `true` if this char is a control character according to unicode.
-  def control?
+  def control? : Bool
     ascii? ? ascii_control? : Unicode.control?(self)
   end
 
   # Returns `true` if this is char is a mark character according to unicode.
-  def mark?
+  def mark? : Bool
     Unicode.mark?(self)
   end
 
@@ -521,7 +521,7 @@ struct Char
   # 'あ'.dump      # => "'\\u{3042}'"
   # '\u0012'.dump # => "'\\u{12}'"
   # ```
-  def dump
+  def dump : String
     dump_or_inspect do |io|
       if ascii_control? || ord >= 0x80
         io << "\\u{"
@@ -637,7 +637,7 @@ struct Char
   # '8'.to_f # => 8.0
   # 'c'.to_f # raises ArgumentError
   # ```
-  def to_f
+  def to_f : Float64
     to_f64
   end
 
@@ -649,27 +649,27 @@ struct Char
   # '8'.to_f? # => 8.0
   # 'c'.to_f? # => nil
   # ```
-  def to_f?
+  def to_f? : Float64?
     to_f64?
   end
 
   # See also: `to_f`.
-  def to_f32
+  def to_f32 : Float32
     to_i.to_f32
   end
 
   # See also: `to_f?`.
-  def to_f32?
+  def to_f32? : Float32?
     to_i?.try &.to_f32
   end
 
   # Same as `to_f`.
-  def to_f64
+  def to_f64 : Float64
     to_i.to_f64
   end
 
   # Same as `to_f?`.
-  def to_f64?
+  def to_f64? : Float64?
     to_i?.try &.to_f64
   end
 
@@ -732,7 +732,7 @@ struct Char
   # 'a'.bytesize # => 1
   # '好'.bytesize # => 3
   # ```
-  def bytesize
+  def bytesize : Int32
     # See http://en.wikipedia.org/wiki/UTF-8#Sample_code
 
     c = ord
@@ -759,7 +759,7 @@ struct Char
   # 'a'.bytes # => [97]
   # 'あ'.bytes # => [227, 129, 130]
   # ```
-  def bytes
+  def bytes : Array(UInt8)
     bytes = [] of UInt8
     each_byte do |byte|
       bytes << byte

src/char/reader.cr

@@ -82,7 +82,7 @@ struct Char
     # reader.has_next?      # => true
     # reader.peek_next_char # => '\0'
     # ```
-    def has_next?
+    def has_next? : Bool
       !@end
     end
 
@@ -94,7 +94,7 @@ struct Char
     # reader = Char::Reader.new("ab")
     # reader.next_char # => 'b'
     # ```
-    def next_char
+    def next_char : Char
       @pos += @current_char_width
       if @pos > @string.bytesize
         raise IndexError.new
@@ -113,7 +113,7 @@ struct Char
     # reader.peek_next_char # => 'b'
     # reader.current_char   # => 'a'
     # ```
-    def peek_next_char
+    def peek_next_char : Char
       next_pos = @pos + @current_char_width
 
       if next_pos > @string.bytesize
@@ -127,7 +127,7 @@ struct Char
 
     # Returns `true` if there are characters before
     # the current one.
-    def has_previous?
+    def has_previous? : Bool
       @pos > 0
     end
 

src/int.cr

@@ -67,7 +67,7 @@ struct Int
   # ```
   # 97.chr # => 'a'
   # ```
-  def chr
+  def chr : Char
     unless 0 <= self <= Char::MAX_CODEPOINT
       raise ArgumentError.new("#{self} out of char range")
     end

src/levenshtein.cr

@@ -104,7 +104,7 @@ module Levenshtein
       end
     end
 
-    def best_match
+    def best_match : String?
       @best_entry.try &.value
     end
 
@@ -114,7 +114,7 @@ module Levenshtein
       sn.best_match
     end
 
-    def self.find(name, all_names, tolerance = nil)
+    def self.find(name, all_names, tolerance = nil) : String?
       find(name, tolerance) do |similar|
         all_names.each do |a_name|
           similar.test(a_name)

src/regex.cr

@@ -267,7 +267,7 @@ class Regex
   # Regex.error?("(foo|bar)") # => nil
   # Regex.error?("(foo|bar")  # => "missing ) at 8"
   # ```
-  def self.error?(source)
+  def self.error?(source) : String?
     re = LibPCRE.compile(source, (Options::UTF_8 | Options::NO_UTF8_CHECK | Options::DUPNAMES), out errptr, out erroffset, nil)
     if re
       nil
@@ -368,7 +368,7 @@ class Regex
   # re.match("Skiing")   # => Regex::MatchData("Skiing")
   # re.match("sledding") # => Regex::MatchData("sledding")
   # ```
-  def +(other)
+  def +(other) : Regex
     Regex.union(self, other)
   end
 
@@ -421,7 +421,7 @@ class Regex
   # /at/ =~ "input data" # => 7
   # /ax/ =~ "input data" # => nil
   # ```
-  def =~(other : String)
+  def =~(other : String) : Int32?
     match = self.match(other)
     $~ = match
     match.try &.begin(0)