From 46e57a27468bfdf88cc33c1fa1f598b7e2d799c4 Mon Sep 17 00:00:00 2001
From: Ary Borenszweig <aborenszweig@manas.com.ar>
Date: Thu, 31 Mar 2016 16:14:02 -0300
Subject: [PATCH] Added `Path#resolve` macro method. Related to #2388

---
 docs/macros.cr                         | 11 ++++++++---
 spec/compiler/codegen/macro_spec.cr    | 12 ++++++++++++
 src/compiler/crystal/macros/macros.cr  | 13 ++++++++-----
 src/compiler/crystal/macros/methods.cr |  9 +++++++++
 4 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/docs/macros.cr b/docs/macros.cr
index 58076a5d446b..b3f876b49916 100644
--- a/docs/macros.cr
+++ b/docs/macros.cr
@@ -785,9 +785,14 @@ module Macros
   # class ImplicitObj < ASTNode
   # end
 
-  # A Path to a constant, like `Foo` or `Foo::Bar::Baz`.
-  # class Path < ASTNode
-  # end
+  # A Path to a constant or type, like `Foo` or `Foo::Bar::Baz`.
+  class Path < ASTNode
+    # Resolves this path to a `TypeNode` if it denotes a type, to
+    # the value of a constant if it denotes a constant, or otherwise
+    # gives a compile-time error.
+    def resolve : ASTNode
+    end
+  end
 
   # A class definition.
   # class ClassDef < ASTNode
diff --git a/spec/compiler/codegen/macro_spec.cr b/spec/compiler/codegen/macro_spec.cr
index 9ddbcc74366e..e1c439635b36 100644
--- a/spec/compiler/codegen/macro_spec.cr
+++ b/spec/compiler/codegen/macro_spec.cr
@@ -1257,4 +1257,16 @@ describe "Code gen: macro" do
       x.foo
       )).to_i.should eq(1)
   end
+
+  it "expands Path with resolve method" do
+    run(%(
+      A = 1
+
+      macro id(path)
+        {{path.resolve}}
+      end
+
+      id(A)
+      )).to_i.should eq(1)
+  end
 end
diff --git a/src/compiler/crystal/macros/macros.cr b/src/compiler/crystal/macros/macros.cr
index 53ffb4db9b3d..123f2113291d 100644
--- a/src/compiler/crystal/macros/macros.cr
+++ b/src/compiler/crystal/macros/macros.cr
@@ -490,6 +490,11 @@ module Crystal
       end
 
       def visit(node : Path)
+        @last = resolve(node)
+        false
+      end
+
+      def resolve(node : Path)
         if node.names.size == 1 && (match = @free_vars.try &.[node.names.first])
           matched_type = match
         else
@@ -502,16 +507,14 @@ module Crystal
 
         case matched_type
         when Const
-          @last = matched_type.value
+          matched_type.value
         when Type
-          @last = TypeNode.new(matched_type)
+          TypeNode.new(matched_type)
         when ASTNode
-          @last = matched_type
+          matched_type
         else
           node.raise "can't interpret #{node}"
         end
-
-        false
       end
 
       def visit(node : Splat)
diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index d295761eb016..55ed525ccb01 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -1016,6 +1016,15 @@ module Crystal
   end
 
   class Path
+    def interpret(method, args, block, interpreter)
+      case method
+      when "resolve"
+        interpret_argless_method(method, args) { interpreter.resolve(self) }
+      else
+        super
+      end
+    end
+
     def to_macro_id
       @names.join "::"
     end