Allow new formatter styles for trailing comma and whitespace around proc literal (#14726)

In preparation of changing the formatter style, this change accepts the new style without enforcing it. Existing code is not affected (this will happen in a follow-up).

Co-authored-by: Johannes Müller <[email protected]>

Author: Blacksmoke16

spec/compiler/formatter/formatter_spec.cr

@@ -1,8 +1,8 @@
 require "spec"
 require "../../../src/compiler/crystal/formatter"
 
-private def assert_format(input, output = input, strict = false, flags = nil, file = __FILE__, line = __LINE__)
-  it "formats #{input.inspect}", file, line do
+private def assert_format(input, output = input, strict = false, flags = nil, file = __FILE__, line = __LINE__, focus = false)
+  it "formats #{input.inspect}", file, line, focus: focus do
     output = "#{output}\n" unless strict
     result = Crystal.format(input, flags: flags)
     unless result == output
@@ -812,7 +812,7 @@ describe Crystal::Formatter do
       end
       CRYSTAL
       def foo(x,
-              y)
+              y,)
         yield
       end
       CRYSTAL
@@ -888,7 +888,7 @@ describe Crystal::Formatter do
       end
       CRYSTAL
       def foo(
-        x
+        x,
       )
         yield
       end
@@ -901,6 +901,39 @@ describe Crystal::Formatter do
       CRYSTAL
   end
 
+  # Allows trailing commas, but doesn't enforce them
+  assert_format <<-CRYSTAL
+    def foo(
+      a,
+      b
+    )
+    end
+    CRYSTAL
+
+  assert_format <<-CRYSTAL
+    def foo(
+      a,
+      b,
+    )
+    end
+    CRYSTAL
+
+  assert_format <<-CRYSTAL
+    macro foo(
+      a,
+      *b,
+    )
+    end
+    CRYSTAL
+
+  assert_format <<-CRYSTAL
+    macro foo(
+      a,
+      **b,
+    )
+    end
+    CRYSTAL
+
   context "adds trailing comma to def multi-line normal, splat, and double splat parameters" do
     assert_format <<-CRYSTAL, <<-CRYSTAL, flags: %w[def_trailing_comma]
       macro foo(
@@ -1693,6 +1726,13 @@ describe Crystal::Formatter do
   assert_format "-> : Int32 {}", "-> : Int32 { }", flags: %w[proc_literal_whitespace]
   assert_format "->do\nend", "-> do\nend", flags: %w[proc_literal_whitespace]
 
+  # Allows whitespace around proc literal, but doesn't enforce them
+  assert_format "-> { }"
+  assert_format "-> { 1 }"
+  assert_format "->(x : Int32) { }"
+  assert_format "-> : Int32 { }"
+  assert_format "-> do\nend"
+
   assert_format "-> : Int32 {}"
   assert_format "-> : Int32 | String { 1 }"
   assert_format "-> : Array(Int32) {}"
@@ -1703,7 +1743,7 @@ describe Crystal::Formatter do
   assert_format "-> : {Int32} { String }"
   assert_format "-> : {x: Int32, y: String} {}"
   assert_format "->\n:\nInt32\n{\n}", "-> : Int32 {\n}"
-  assert_format "->( x )\n:\nInt32 { }", "->(x) : Int32 {}"
+  assert_format "->( x )\n:\nInt32 { }", "->(x) : Int32 { }"
   assert_format "->: Int32 do\nx\nend", "-> : Int32 do\n  x\nend"
 
   {:+, :-, :*, :/, :^, :>>, :<<, :|, :&, :&+, :&-, :&*, :&**}.each do |sym|

src/compiler/crystal/tools/formatter.cr

@@ -1651,7 +1651,7 @@ module Crystal
       yield
 
       # Write "," before skipping spaces to prevent inserting comment between argument and comma.
-      write "," if has_more || (write_trailing_comma && flag?("def_trailing_comma"))
+      write "," if has_more || (wrote_newline && @token.type.op_comma?) || (write_trailing_comma && flag?("def_trailing_comma"))
 
       just_wrote_newline = skip_space
       if @token.type.newline?
@@ -4242,6 +4242,7 @@ module Crystal
 
     def visit(node : ProcLiteral)
       write_token :OP_MINUS_GT
+      whitespace_after_op_minus_gt = @token.type.space?
       skip_space_or_newline
 
       a_def = node.def
@@ -4272,15 +4273,15 @@ module Crystal
         skip_space_or_newline
       end
 
-      write " " if a_def.args.present? || return_type || flag?("proc_literal_whitespace")
+      write " " if a_def.args.present? || return_type || flag?("proc_literal_whitespace") || whitespace_after_op_minus_gt
 
       is_do = false
       if @token.keyword?(:do)
         write_keyword :do
         is_do = true
       else
         write_token :OP_LCURLY
-        write " " if a_def.body.is_a?(Nop) && flag?("proc_literal_whitespace")
+        write " " if a_def.body.is_a?(Nop) && (flag?("proc_literal_whitespace") || @token.type.space?)
       end
       skip_space