Formatter: Handle leading tuple literals in multi-expression return/break/next properly

spec/compiler/formatter/formatter_spec.cr

@@ -342,7 +342,15 @@ describe Crystal::Formatter do
     assert_format "#{keyword}  1", "#{keyword} 1"
     assert_format "#{keyword}( 1 , 2 )", "#{keyword}(1, 2)"
     assert_format "#{keyword}  1 ,  2", "#{keyword} 1, 2"
-    assert_format "#{keyword} { 1 ,  2 }", "#{keyword} {1, 2}" unless keyword == "yield"
+
+    unless keyword == "yield"
+      assert_format "#{keyword} { 1 ,  2 }", "#{keyword} {1, 2}"
+      assert_format "#{keyword} {1, 2}, 3"
+      assert_format "#{keyword} 1, {2, 3}"
+      assert_format "#{keyword} {1, 2}, {3, 4}"
+      assert_format "#{keyword} { {1, 2}, {3, 4} }"
+      assert_format "#{keyword} { {1, 2}, {3, 4} }, 5"
+    end
   end
 
   assert_format "yield 1\n2", "yield 1\n2"

src/compiler/crystal/syntax/lexer.cr

@@ -55,6 +55,7 @@ module Crystal
     def initialize(string, string_pool : StringPool? = nil)
       @reader = Char::Reader.new(string)
       @token = Token.new
+      @temp_token = Token.new
       @line_number = 1
       @column_number = 1
       @filename = ""
@@ -2524,14 +2525,23 @@ module Crystal
       @token
     end
 
-    def lookahead
-      old_pos = @reader.pos
-      old_line_number, old_column_number = @line_number, @column_number
+    def lookahead(preserve_token_on_fail = false)
+      old_pos, old_line, old_column = current_pos, @line_number, @column_number
+      @temp_token.copy_from(@token) if preserve_token_on_fail
 
       result = yield
       unless result
-        @reader.pos = old_pos
-        @line_number, @column_number = old_line_number, old_column_number
+        self.current_pos, @line_number, @column_number = old_pos, old_line, old_column
+        @token.copy_from(@temp_token) if preserve_token_on_fail
+      end
+      result
+    end
+
+    def peek_ahead
+      result = uninitialized typeof(yield)
+      lookahead(preserve_token_on_fail: true) do
+        result = yield
+        nil
       end
       result
     end

src/compiler/crystal/syntax/parser.cr

@@ -26,7 +26,6 @@ module Crystal
 
     def initialize(str, string_pool : StringPool? = nil, @def_vars = [Set(String).new])
       super(str, string_pool)
-      @temp_token = Token.new
       @unclosed_stack = [] of Unclosed
       @calls_super = false
       @calls_initialize = false
@@ -624,12 +623,7 @@ module Crystal
           end
 
           # Allow '.' after newline for chaining calls
-          old_pos, old_line, old_column = current_pos, @line_number, @column_number
-          @temp_token.copy_from @token
-          next_token_skip_space_or_newline
-          unless @token.type == :"."
-            self.current_pos, @line_number, @column_number = old_pos, old_line, old_column
-            @token.copy_from @temp_token
+          unless lookahead(preserve_token_on_fail: true) { next_token_skip_space_or_newline; @token.type == :"." }
             break
           end
         when :"."
@@ -965,21 +959,10 @@ module Crystal
         location = @token.location
         var = Var.new(@token.to_s).at(location)
 
-        old_pos, old_line, old_column = current_pos, @line_number, @column_number
-        @temp_token.copy_from(@token)
-
-        next_token_skip_space
-
-        if @token.type == :"="
-          @token.copy_from(@temp_token)
-          self.current_pos, @line_number, @column_number = old_pos, old_line, old_column
-
+        if peek_ahead { next_token_skip_space; @token.type == :"=" }
           push_var var
           node_and_next_token var
         else
-          @token.copy_from(@temp_token)
-          self.current_pos, @line_number, @column_number = old_pos, old_line, old_column
-
           node_and_next_token Global.new(var.name).at(location)
         end
       when :GLOBAL_MATCH_DATA_INDEX
@@ -5085,20 +5068,18 @@ module Crystal
 
     # Looks ahead next tokens to check whether they indicate type.
     def type_start?(*, consume_newlines)
-      old_pos, old_line, old_column = current_pos, @line_number, @column_number
-      @temp_token.copy_from(@token)
+      peek_ahead do
+        begin
+          if consume_newlines
+            next_token_skip_space_or_newline
+          else
+            next_token_skip_space
+          end
 
-      begin
-        if consume_newlines
-          next_token_skip_space_or_newline
-        else
-          next_token_skip_space
+          type_start?
+        rescue
+          false
         end
-
-        type_start?
-      ensure
-        @token.copy_from(@temp_token)
-        self.current_pos, @line_number, @column_number = old_pos, old_line, old_column
       end
     end
 

src/compiler/crystal/tools/formatter.cr

@@ -3568,7 +3568,16 @@ module Crystal
         write " " unless has_parentheses
         skip_space
 
-        if exp.is_a?(TupleLiteral) && @token.type != :"{"
+        # If the number of consecutive `{`s starting a tuple literal is 1 less
+        # than the level of tuple nesting in the actual AST node, this means the
+        # parser synthesized a TupleLiteral from multiple expressions, e.g.
+        #
+        #     return {1, 2}, 3, 4
+        #     return { {1, 2}, 3, 4 }
+        #
+        # The tuple depth is 2 in both cases but only 1 leading curly brace is
+        # present on the first return.
+        if exp.is_a?(TupleLiteral) && opening_curly_brace_count < leading_tuple_depth(exp)
           format_args(exp.elements, has_parentheses)
           skip_space if has_parentheses
         else
@@ -3582,6 +3591,26 @@ module Crystal
       false
     end
 
+    def opening_curly_brace_count
+      @lexer.peek_ahead do
+        count = 0
+        while @lexer.token.type == :"{"
+          count += 1
+          @lexer.next_token_skip_space_or_newline
+        end
+        count
+      end
+    end
+
+    def leading_tuple_depth(exp)
+      count = 0
+      while exp.is_a?(TupleLiteral)
+        count += 1
+        exp = exp.elements.first?
+      end
+      count
+    end
+
     def visit(node : Yield)
       if scope = node.scope
         write_keyword :with, " "