Honour pre-processor if/unless statements (fixes #413)

Introduce pre-processed if directives to hide code from Opal. Two special constant checks now take place in the compiler. Either `RUBY_ENGINE` or `RUBY_PLATFORM` when `== "opal"`. Both if and unless statements can pick up these logic checks: if RUBY_ENGINE == "opal" # this code compiles else # this code never compiles end Unless: unless RUBY_ENGINE == "opal" # this code never compiles end This is particularly useful for avoiding `require()` statements being picked up, which are included at compile time.
opal · Dec 8, 2013 · ef570e3 · ef570e3
1 parent 8f646bc
commit ef570e3
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Showing 3 changed files with 102 additions and 9 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,26 @@
     next release, the exernal `opal-sprockets` gem is no longer needed. This
     commit adds `Opal::Processor`, `Opal::Server` and `Opal::Environment`.
 
+*   Introduce pre-processed if directives to hide code from Opal. Two special
+    constant checks now take place in the compiler. Either `RUBY_ENGINE` or
+    `RUBY_PLATFORM` when `== "opal"`. Both if and unless statements can pick
+    up these logic checks:
+
+        if RUBY_ENGINE == "opal"
+          # this code compiles
+        else
+          # this code never compiles
+        end
+
+    Unless:
+
+        unless RUBY_ENGINE == "opal"
+          # this code never compiles
+        end
+
+    This is particularly useful for avoiding `require()` statements being
+    picked up, which are included at compile time.
+
 *   Add special `debugger` method to compiler. Compiles down to javascript
     `debugger` keyword to start in-browser debug console.
 

diff --git a/lib/opal/nodes/if.rb b/lib/opal/nodes/if.rb
@@ -7,21 +7,20 @@ class IfNode < Base
 
       children :test, :true_body, :false_body
 
+      RUBY_ENGINE_CHECK = [:call, [:const, :RUBY_ENGINE],
+                              :==, [:arglist, [:str, "opal"]]]
+
+      RUBY_PLATFORM_CHECK = [:call, [:const, :RUBY_PLATFORM],
+                              :==, [:arglist, [:str, "opal"]]]
+
       def compile
         truthy, falsy = self.truthy, self.falsy
 
-        push "if ("
-
-        # optimize unless (we don't want a else() unless we need to)
-        if falsy and !truthy
-          truthy = falsy
+        if skip_check_present?
           falsy = nil
-          push js_falsy(test)
-        else
-          push js_truthy(test)
         end
 
-        push ") {"
+        push "if (", js_truthy(test), ") {"
 
         # skip if-body if no truthy sexp
         indent { line stmt(truthy) } if truthy
@@ -44,6 +43,14 @@ def compile
         wrap "(function() {", "; return nil; })()" if needs_wrapper?
       end
 
+      # pre-processing only effects falsy blocks. If engine is
+      # opal, then falsy block gets generated as normal. Unless
+      # engine is opal then that code gets generated as the
+      # falsy block
+      def skip_check_present?
+        test == RUBY_ENGINE_CHECK or test == RUBY_PLATFORM_CHECK
+      end
+
       def truthy
         needs_wrapper? ? compiler.returns(true_body || s(:nil)) : true_body
       end

diff --git a/spec/cli/compiler_spec.rb b/spec/cli/compiler_spec.rb
@@ -64,6 +64,72 @@
     end
   end
 
+  describe "pre-processed if conditions" do
+    it "compiles if blocks using RUBY_ENGINE/RUBY_PLATFORM == opal" do
+      expect_compiled(<<-RUBY).to include("should_compile_fine")
+        if RUBY_ENGINE == 'opal'
+          :should_compile_fine
+        end
+      RUBY
+
+      expect_compiled(<<-RUBY).to include("so_should_this")
+        if RUBY_PLATFORM == 'opal'
+          :so_should_this
+        end
+      RUBY
+    end
+
+    it "skips elsif/else parts" do
+      expect_compiled(<<-RUBY).to_not include("should_be_skipped")
+        if RUBY_PLATFORM == "opal"
+          :ok
+        else
+          :should_be_skipped
+        end
+      RUBY
+
+      result = expect_compiled(<<-RUBY)
+        if RUBY_ENGINE == 'opal'
+          :this_compiles
+        elsif false
+          :this_does_not_compile
+        else
+          :this_neither
+        end
+      RUBY
+
+      result.to_not include("this_does_not_compile", "this_neither")
+    end
+
+    it "generates if-code as normal without check" do
+      expect_compiled(<<-RUBY).to include("should_compile", "and_this")
+        if some_conditional
+          :should_compile
+        else
+          :and_this
+        end
+      RUBY
+    end
+  end
+
+  describe "pre-processed unless conditionals" do
+    it "skips over if using RUBY_ENGINE/RUBY_PLATFORM == 'opal'" do
+      expect_compiled(<<-RUBY).to_not include("should_not_compile")
+        unless RUBY_ENGINE == 'opal'
+          :should_not_compile
+        end
+      RUBY
+    end
+
+    it "generates unless code as normal if no check" do
+      expect_compiled(<<-RUBY).to include("this_should_compile")
+        unless this_is_true
+          :this_should_compile
+        end
+      RUBY
+    end
+  end
+
   def expect_compiled(source)
     expect(Opal::Compiler.new.compile source)
   end