Macros: try call for unknown var

src/compiler/crystal/macros.cr

@@ -15,8 +15,7 @@ module Crystal::Macros
   end
 
   # Outputs the current macro's buffer to the standard output. Useful for debugging
-  # a macro to see what's being generated. Use it like `{{debug()}}`, the parenthesis
-  # are mandatory.
+  # a macro to see what's being generated.
   #
   # By default, the output is tried to be formatted using Crystal's
   # formatter, but you can disable this by passing `false` to this method.
@@ -107,7 +106,7 @@ module Crystal::Macros
   #
   # ```
   # # sth_for_osx.cr
-  # {% skip() unless flag?(:darwin) %}
+  # {% skip unless flag?(:darwin) %}
   #
   # # Class FooForMac will only be defined if we're compiling on OS X
   # class FooForMac

src/compiler/crystal/macros/interpreter.cr

@@ -117,10 +117,25 @@ module Crystal
     def visit(node : Var)
       var = @vars[node.name]?
       if var
-        @last = var
-      else
-        node.raise "undefined macro variable '#{node.name}'"
+        return @last = var
+      end
+
+      # Try to consider the var as a top-level macro call.
+      #
+      # Note: this should really be done at the parser level. However,
+      # currently macro calls with blocks are possible, for example:
+      #
+      # some_macro_call do |arg|
+      #   {{arg}}
+      # end
+      #
+      # and in this case the parser has no idea about this, so the only
+      # solution is to do it now.
+      if value = interpret_top_level_call?(Call.new(nil, node.name))
+        return @last = value
       end
+
+      node.raise "undefined macro variable '#{node.name}'"
     end
 
     def visit(node : StringInterpolation)

src/compiler/crystal/macros/methods.cr

@@ -5,6 +5,11 @@ require "semantic_version"
 module Crystal
   class MacroInterpreter
     def interpret_top_level_call(node)
+      interpret_top_level_call?(node) ||
+        node.raise("undefined macro method: '#{node.name}'")
+    end
+
+    def interpret_top_level_call?(node)
       # Please order method names in lexicographical order, because OCD
       case node.name
       when "compare_versions"
@@ -28,7 +33,7 @@ module Crystal
       when "run"
         interpret_run(node)
       else
-        node.raise "undefined macro method: '#{node.name}'"
+        nil
       end
     end