Relax whitespace requirement around operators. (#706)

spec/examples/pipe

@@ -64,3 +64,15 @@ component Main {
     ""
   }
 }
+-------------------------------------------------------------------------------
+component Main {
+  fun test (value : String) {
+    value
+  }
+
+  fun render : Html {
+    "test" |> test
+
+    <div/>
+  }
+}

src/parser/top_level.cr

@@ -79,7 +79,6 @@ module Mint
             component ||
             constant ||
             property ||
-            operator ||
             provider ||
             function ||
             comment ||

src/parsers/operator.cr

@@ -26,40 +26,63 @@ module Mint
       "!"  => 16,
     }
 
-    # Parses an operator.
-    #
-    # All operators must follow a whitespace because we don't have an end of
-    # line token, so the expression can leak through to the next entity, for
-    # example:
-    #
-    #   const NAME = "Joe"
-    #
-    #   /* This is a comment. */
-    #   fun greet (name : String = NAME) { ... }
-    #
-    # In this case the start token of the comment (/*) can be interpreted as an
-    # operation (/) and the whitespace prevents that.
     def operator : String?
-      parse do
+      parse do |start_position|
         whitespace
 
         saved_position =
           position
 
         operator =
-          OPERATORS.keys.find { |item| word! item }
+          OPERATORS.keys.find { |item| word? item }
 
         next unless operator
-        next if operator != "|>" && !whitespace?
+
+        case operator
+        when "<"
+          # If we are in a different line then left side then it's probably
+          # not a operation:
+          #
+          #   Left side
+          #   |---|
+          #   <div>
+          #      <div>
+          #      |
+          #      Potential operator
+          #
+          next if start_position.line < position.line
+
+          # If the right side parses as a base expression:
+          #
+          # Left side  Right side
+          #     |---|  |---|
+          #     <div>  <div>
+          #            |
+          #            Potential operator
+          #
+          next if parse { whitespace; base_expression }
+
+          # This prevents the this to parse as a regexp literal:
+          #
+          # Start tag  Variable   Potential operator
+          # |---|      |-------|  |
+          # <div>       variable  </div>
+          #                        |
+          #                        Regexp literal start
+          #
+          next if next_char == '/'
+        when "/"
+          # It's probably a comment (`// comment`, `/* comment */`)
+          next if next_char.in?('*', '/')
+        end
+
+        word! operator
 
         case operator
         when "or"
           # This is not an operation but part of a statements
-          # "or return" section.
-          next if parse do
-                    whitespace
-                    keyword! "return"
-                  end
+          # `or return` section.
+          next if parse { whitespace; keyword! "return" }
 
           ast.keywords << {from: saved_position, to: saved_position + operator.size}
         else