ruby--ruby/spec/ruby/language/pattern_matching_spec.rb

require_relative '../spec_helper'

ruby_version_is "2.7" do
  describe "Pattern matching" do
    # TODO: Remove excessive eval calls when support of previous version
    #       Ruby 2.6 will be dropped

    before do
      ScratchPad.record []
    end

    it "can be standalone in operator that deconstructs value" do
      eval(<<-RUBY).should == [0, 1]
        [0, 1] in [a, b]
        [a, b]
      RUBY
    end

    it "extends case expression with case/in construction" do
      eval(<<~RUBY).should == :bar
        case [0, 1]
          in [0]
            :foo
          in [0, 1]
            :bar
        end
      RUBY
    end

    it "allows using then operator" do
      eval(<<~RUBY).should == :bar
        case [0, 1]
          in [0]    then :foo
          in [0, 1] then :bar
        end
      RUBY
    end

    it "warns about pattern matching is experimental feature" do
      -> {
        eval <<~RUBY
          case 0
            in 0
          end
        RUBY
      }.should complain(/warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!/)
    end

    it "binds variables" do
      eval(<<~RUBY).should == 1
        case [0, 1]
          in [0, a]
            a
        end
      RUBY
    end

    it "cannot mix in and when operators" do
      -> {
        eval <<~RUBY
          case []
            when 1 == 1
            in []
          end
        RUBY
      }.should raise_error(SyntaxError, /syntax error, unexpected `in'/)

      -> {
        eval <<~RUBY
          case []
            in []
            when 1 == 1
          end
        RUBY
      }.should raise_error(SyntaxError, /syntax error, unexpected `when'/)
    end

    it "checks patterns until the first matching" do
      eval(<<~RUBY).should == :bar
        case [0, 1]
          in [0]
            :foo
          in [0, 1]
            :bar
          in [0, 1]
            :baz
        end
      RUBY
    end

    it "executes else clause if no pattern matches" do
      eval(<<~RUBY).should == false
        case [0, 1]
          in [0]
            true
          else
            false
        end
      RUBY
    end

    it "raises NoMatchingPatternError if no pattern matches and no else clause" do
      -> {
        eval <<~RUBY
          case [0, 1]
            in [0]
          end
        RUBY
      }.should raise_error(NoMatchingPatternError, /\[0, 1\]/)
    end

    it "does not allow calculation or method calls in a pattern" do
      -> {
        eval <<~RUBY
          case 0
            in 1 + 1
              true
          end
        RUBY
      }.should raise_error(SyntaxError, /unexpected/)
    end

    describe "guards" do
      it "supports if guard" do
        eval(<<~RUBY).should == false
          case 0
            in 0 if false
              true
          else
            false
          end
        RUBY

        eval(<<~RUBY).should == true
          case 0
            in 0 if true
              true
          else
            false
          end
        RUBY
      end

      it "supports unless guard" do
        eval(<<~RUBY).should == false
          case 0
            in 0 unless true
              true
          else
            false
          end
        RUBY

        eval(<<~RUBY).should == true
          case 0
            in 0 unless false
              true
          else
            false
          end
        RUBY
      end

      it "makes bound variables visible in guard" do
        eval(<<~RUBY).should == true
          case [0, 1]
            in [a, 1] if a >= 0
              true
          end
        RUBY
      end

      it "does not evaluate guard if pattern does not match" do
        eval <<~RUBY
          case 0
            in 1 if (ScratchPad << :foo) || true
          else
          end
        RUBY

        ScratchPad.recorded.should == []
      end

      it "takes guards into account when there are several matching patterns" do
        eval(<<~RUBY).should == :bar
          case 0
            in 0 if false
              :foo
            in 0 if true
              :bar
          end
        RUBY
      end

      it "executes else clause if no guarded pattern matches" do
        eval(<<~RUBY).should == false
          case 0
            in 0 if false
              true
          else
            false
          end
        RUBY
      end

      it "raises NoMatchingPatternError if no guarded pattern matches and no else clause" do
        -> {
          eval <<~RUBY
            case [0, 1]
              in [0, 1] if false
            end
          RUBY
        }.should raise_error(NoMatchingPatternError, /\[0, 1\]/)
      end
    end

    describe "value pattern" do
      it "matches an object such that pattern === object" do
        eval(<<~RUBY).should == true
          case 0
            in 0
              true
          end
        RUBY

        eval(<<~RUBY).should == true
          case 0
            in (-1..1)
              true
          end
        RUBY

        eval(<<~RUBY).should == true
          case 0
            in Integer
              true
          end
        RUBY

        eval(<<~RUBY).should == true
          case "0"
            in /0/
              true
          end
        RUBY

        eval(<<~RUBY).should == true
          case "0"
            in ->(s) { s == "0" }
              true
          end
        RUBY
      end

      it "allows string literal with interpolation" do
        x = "x"

        eval(<<~RUBY).should == true
          case "x"
            in "#{x + ""}"
              true
          end
        RUBY
      end
    end

    describe "variable pattern" do
      it "matches a value and binds variable name to this value" do
        eval(<<~RUBY).should == 0
          case 0
            in a
              a
          end
        RUBY
      end

      it "makes bounded variable visible outside a case statement scope" do
        eval(<<~RUBY).should == 0
          case 0
            in a
          end

          a
        RUBY
      end

      it "create local variables even if a pattern doesn't match" do
        eval(<<~RUBY).should == [0, nil, nil]
          case 0
            in a
            in b
            in c
          end

          [a, b, c]
        RUBY
      end

      it "allow using _ name to drop values" do
        eval(<<~RUBY).should == 0
          case [0, 1]
            in [a, _]
              a
          end
        RUBY
      end

      it "supports using _ in a pattern several times" do
        eval(<<~RUBY).should == 2
          case [0, 1, 2]
            in [0, _, _]
              _
          end
        RUBY
      end

      it "supports using any name with _ at the beginning in a pattern several times" do
        eval(<<~RUBY).should == 2
          case [0, 1, 2]
            in [0, _x, _x]
              _x
          end
        RUBY

        eval(<<~RUBY).should == 2
          case {a: 0, b: 1, c: 2}
            in {a: 0, b: _x, c: _x}
              _x
          end
        RUBY
      end

      it "does not support using variable name (except _) several times" do
        -> {
          eval <<~RUBY
            case [0]
              in [a, a]
            end
          RUBY
        }.should raise_error(SyntaxError, /duplicated variable name/)
      end

      it "supports existing variables in a pattern specified with ^ operator" do
        a = 0

        eval(<<~RUBY).should == true
          case 0
            in ^a
              true
          end
        RUBY
      end

      it "allows applying ^ operator to bound variables" do
        eval(<<~RUBY).should == 1
          case [1, 1]
            in [n, ^n]
              n
          end
        RUBY

        eval(<<~RUBY).should == false
          case [1, 2]
            in [n, ^n]
              true
          else
            false
          end
        RUBY
      end

      it "requires bound variable to be specified in a pattern before ^ operator when it relies on a bound variable" do
        -> {
          eval <<~RUBY
            case [1, 2]
              in [^n, n]
                true
            else
              false
            end
          RUBY
        }.should raise_error(SyntaxError, /n: no such local variable/)
      end
    end

    describe "alternative pattern" do
      it "matches if any of patterns matches" do
        eval(<<~RUBY).should == true
          case 0
            in 0 | 1 | 2
              true
          end
        RUBY
      end

      it "does not support variable binding" do
        -> {
          eval <<~RUBY
            case [0, 1]
              in [0, 0] | [0, a]
            end
          RUBY
        }.should raise_error(SyntaxError, /illegal variable in alternative pattern/)
      end
    end

    describe "AS pattern" do
      it "binds a variable to a value if pattern matches" do
        eval(<<~RUBY).should == 0
          case 0
            in Integer => n
              n
          end
        RUBY
      end

      it "can be used as a nested pattern" do
        eval(<<~RUBY).should == [2, 3]
          case [1, [2, 3]]
            in [1, Array => ary]
              ary
          end
        RUBY
      end
    end

    describe "Array pattern" do
      it "supports form Constant(pat, pat, ...)" do
        eval(<<~RUBY).should == true
          case [0, 1, 2]
            in Array(0, 1, 2)
              true
          end
        RUBY
      end

      it "supports form Constant[pat, pat, ...]" do
        eval(<<~RUBY).should == true
          case [0, 1, 2]
            in Array[0, 1, 2]
              true
          end
        RUBY
      end

      it "supports form [pat, pat, ...]" do
        eval(<<~RUBY).should == true
          case [0, 1, 2]
            in [0, 1, 2]
              true
          end
        RUBY
      end

      it "supports form pat, pat, ..." do
        eval(<<~RUBY).should == true
          case [0, 1, 2]
            in 0, 1, 2
              true
          end
        RUBY

        eval(<<~RUBY).should == 1
          case [0, 1, 2]
            in 0, a, 2
              a
          end
        RUBY

        eval(<<~RUBY).should == [1, 2]
          case [0, 1, 2]
            in 0, *rest
              rest
          end
        RUBY
      end

      it "matches an object with #deconstruct method which returns an array and each element in array matches element in pattern" do
        obj = Object.new
        def obj.deconstruct; [0, 1] end

        eval(<<~RUBY).should == true
          case obj
            in [Integer, Integer]
              true
          end
        RUBY
      end

      it "does not match object if Constant === object returns false" do
        eval(<<~RUBY).should == false
          case [0, 1, 2]
            in String[0, 1, 2]
              true
          else
            false
          end
        RUBY
      end

      it "does not match object without #deconstruct method" do
        obj = Object.new

        eval(<<~RUBY).should == false
          case obj
            in Object[]
              true
          else
            false
          end
        RUBY
      end

      it "raises TypeError if #deconstruct method does not return array" do
        obj = Object.new
        def obj.deconstruct; "" end

        -> {
          eval <<~RUBY
            case obj
              in Object[]
            else
            end
          RUBY
        }.should raise_error(TypeError, /deconstruct must return Array/)
      end

      it "does not match object if elements of array returned by #deconstruct method does not match elements in pattern" do
        obj = Object.new
        def obj.deconstruct; [1] end

        eval(<<~RUBY).should == false
          case obj
            in Object[0]
              true
          else
            false
          end
        RUBY
      end

      it "binds variables" do
        eval(<<~RUBY).should == [0, 1, 2]
          case [0, 1, 2]
            in [a, b, c]
              [a, b, c]
          end
        RUBY
      end

      it "binds variable even if patter matches only partially" do
        a = nil

        eval(<<~RUBY).should == 0
          case [0, 1, 2]
            in [a, 1, 3]
          else
          end

          a
        RUBY
      end

      it "supports splat operator *rest" do
        eval(<<~RUBY).should == [1, 2]
          case [0, 1, 2]
            in [0, *rest]
              rest
          end
        RUBY
      end

      it "does not match partially by default" do
        eval(<<~RUBY).should == false
          case [0, 1, 2, 3]
            in [1, 2]
              true
          else
            false
          end
        RUBY
      end

      it "does match partially from the array beginning if list + , syntax used" do
        eval(<<~RUBY).should == true
          case [0, 1, 2, 3]
            in [0, 1,]
              true
          end
        RUBY

        eval(<<~RUBY).should == true
          case [0, 1, 2, 3]
            in 0, 1,;
              true
          end
        RUBY
      end

      it "matches [] with []" do
        eval(<<~RUBY).should == true
          case []
            in []
              true
          end
        RUBY
      end

      it "matches anything with *" do
        eval(<<~RUBY).should == true
          case [0, 1]
            in *;
              true
          end
        RUBY
      end
    end

    describe "Hash pattern" do
      it "supports form Constant(id: pat, id: pat, ...)" do
        eval(<<~RUBY).should == true
          case {a: 0, b: 1}
            in Hash(a: 0, b: 1)
              true
          end
        RUBY
      end

      it "supports form Constant[id: pat, id: pat, ...]" do
        eval(<<~RUBY).should == true
          case {a: 0, b: 1}
            in Hash[a: 0, b: 1]
              true
          end
        RUBY
      end

      it "supports form {id: pat, id: pat, ...}" do
        eval(<<~RUBY).should == true
          case {a: 0, b: 1}
            in {a: 0, b: 1}
              true
          end
        RUBY
      end

      it "supports form id: pat, id: pat, ..." do
        eval(<<~RUBY).should == true
          case {a: 0, b: 1}
            in a: 0, b: 1
              true
          end
        RUBY

        eval(<<~RUBY).should == [0, 1]
          case {a: 0, b: 1}
            in a: a, b: b
              [a, b]
          end
        RUBY

        eval(<<~RUBY).should == { b: 1, c: 2 }
          case {a: 0, b: 1, c: 2}
            in a: 0, **rest
              rest
          end
        RUBY
      end

      it "supports a: which means a: a" do
        eval(<<~RUBY).should == [0, 1]
          case {a: 0, b: 1}
            in Hash(a:, b:)
              [a, b]
          end
        RUBY

        a = b = nil
        eval(<<~RUBY).should == [0, 1]
          case {a: 0, b: 1}
            in Hash[a:, b:]
              [a, b]
          end
        RUBY

        a = b = nil
        eval(<<~RUBY).should == [0, 1]
          case {a: 0, b: 1}
            in {a:, b:}
              [a, b]
          end
        RUBY

        a = nil
        eval(<<~RUBY).should == [0, {b: 1, c: 2}]
          case {a: 0, b: 1, c: 2}
            in {a:, **rest}
              [a, rest]
          end
        RUBY

        a = b = nil
        eval(<<~RUBY).should == [0, 1]
          case {a: 0, b: 1}
            in a:, b:
              [a, b]
          end
        RUBY
      end

      it "can mix key (a:) and key-value (a: b) declarations" do
        eval(<<~RUBY).should == [0, 1]
          case {a: 0, b: 1}
            in Hash(a:, b: x)
              [a, x]
          end
        RUBY
      end

      it "supports 'string': key literal" do
        eval(<<~RUBY).should == true
          case {a: 0}
            in {"a": 0}
              true
          end
        RUBY
      end

      it "does not support non-symbol keys" do
        -> {
          eval <<~RUBY
            case {a: 1}
              in {"a" => 1}
            end
          RUBY
        }.should raise_error(SyntaxError, /unexpected/)
      end

      it "does not support string interpolation in keys" do
        x = "a"

        -> {
          eval <<~'RUBY'
            case {a: 1}
              in {"#{x}": 1}
            end
          RUBY
        }.should raise_error(SyntaxError, /symbol literal with interpolation is not allowed/)
      end

      it "raise SyntaxError when keys duplicate in pattern" do
        -> {
          eval <<~RUBY
            case {a: 1}
              in {a: 1, b: 2, a: 3}
            end
          RUBY
        }.should raise_error(SyntaxError, /duplicated key name/)
      end

      it "matches an object with #deconstruct_keys method which returns a Hash with equal keys and each value in Hash matches value in pattern" do
        obj = Object.new
        def obj.deconstruct_keys(*); {a: 1} end

        eval(<<~RUBY).should == true
          case obj
            in {a: 1}
              true
          end
        RUBY
      end

      it "does not match object if Constant === object returns false" do
        eval(<<~RUBY).should == false
          case {a: 1}
            in String[a: 1]
              true
          else
            false
          end
        RUBY
      end

      it "does not match object without #deconstruct_keys method" do
        obj = Object.new

        eval(<<~RUBY).should == false
          case obj
            in Object[a: 1]
              true
          else
            false
          end
        RUBY
      end

      it "does not match object if #deconstruct_keys method does not return Hash" do
        obj = Object.new
        def obj.deconstruct_keys(*); "" end

        -> {
          eval <<~RUBY
            case obj
              in Object[a: 1]
            end
          RUBY
        }.should raise_error(TypeError, /deconstruct_keys must return Hash/)
      end

      it "does not match object if #deconstruct_keys method returns Hash with non-symbol keys" do
        obj = Object.new
        def obj.deconstruct_keys(*); {"a" => 1} end

        eval(<<~RUBY).should == false
          case obj
            in Object[a: 1]
              true
          else
            false
          end
        RUBY
      end

      it "does not match object if elements of Hash returned by #deconstruct_keys method does not match values in pattern" do
        obj = Object.new
        def obj.deconstruct_keys(*); {a: 1} end

        eval(<<~RUBY).should == false
          case obj
            in Object[a: 2]
              true
          else
            false
          end
        RUBY
      end

      it "passes keys specified in pattern as arguments to #deconstruct_keys method" do
        obj = Object.new

        def obj.deconstruct_keys(*args)
          ScratchPad << args
          {a: 1, b: 2, c: 3}
        end

        eval <<~RUBY
          case obj
            in Object[a: 1, b: 2, c: 3]
          end
        RUBY

        ScratchPad.recorded.should == [[[:a, :b, :c]]]
      end

      it "passes keys specified in pattern to #deconstruct_keys method if pattern contains double splat operator **" do
        obj = Object.new

        def obj.deconstruct_keys(*args)
          ScratchPad << args
          {a: 1, b: 2, c: 3}
        end

        eval <<~RUBY
          case obj
            in Object[a: 1, b: 2, **]
          end
        RUBY

        ScratchPad.recorded.should == [[[:a, :b]]]
      end

      it "passes nil to #deconstruct_keys method if pattern contains double splat operator **rest" do
        obj = Object.new

        def obj.deconstruct_keys(*args)
          ScratchPad << args
          {a: 1, b: 2}
        end

        eval <<~RUBY
          case obj
            in Object[a: 1, **rest]
          end
        RUBY

        ScratchPad.recorded.should == [[nil]]
      end

      it "binds variables" do
        eval(<<~RUBY).should == [0, 1, 2]
          case {a: 0, b: 1, c: 2}
            in {a: x, b: y, c: z}
              [x, y, z]
          end
        RUBY
      end

      it "binds variable even if pattern matches only partially" do
        x = nil

        eval(<<~RUBY).should == 0
          case {a: 0, b: 1}
            in {a: x, b: 2}
          else
          end

          x
        RUBY
      end

      it "supports double splat operator **rest" do
        eval(<<~RUBY).should == {b: 1, c: 2}
          case {a: 0, b: 1, c: 2}
            in {a: 0, **rest}
              rest
          end
        RUBY
      end

      it "treats **nil like there should not be any other keys in a matched Hash" do
        eval(<<~RUBY).should == true
          case {a: 1, b: 2}
            in {a: 1, b: 2, **nil}
              true
          end
        RUBY

        eval(<<~RUBY).should == false
          case {a: 1, b: 2}
            in {a: 1, **nil}
              true
          else
            false
          end
        RUBY
      end

      it "can match partially" do
        eval(<<~RUBY).should == true
          case {a: 1, b: 2}
            in {a: 1}
              true
          end
        RUBY
      end

      it "matches {} with {}" do
        eval(<<~RUBY).should == true
          case {}
            in {}
              true
          end
        RUBY
      end

      it "matches anything with **" do
        eval(<<~RUBY).should == true
          case {a: 1}
            in **;
              true
          end
        RUBY
      end
    end
  end
end