Environment: rework process()

- improve efficiency
- give errors for the dependency that failed instead of the top-level target

lib/rscons/environment.rb

@@ -125,26 +125,28 @@ module Rscons
     # called after the block returns.
     def process
       cache = Cache.new
-      targets_processed = Set.new
+      targets_processed = {}
       process_target = proc do |target|
-        if @targets[target][:source].map do |src|
-          targets_processed.include?(src) or not @targets.include?(src) or process_target.call(src)
-        end.all?
-          run_builder(@targets[target][:builder],
-                      target,
-                      @targets[target][:source],
-                      cache,
-                      @targets[target][:vars] || {})
-        else
-          false
+        targets_processed[target] ||= begin
+          @targets[target][:source].each do |src|
+            if @targets.include?(src) and not targets_processed.include?(src)
+              process_target.call(src)
+            end
+          end
+          result = run_builder(@targets[target][:builder],
+                               target,
+                               @targets[target][:source],
+                               cache,
+                               @targets[target][:vars] || {})
+          unless result
+            cache.write
+            raise BuildError.new("Failed to build #{target}")
+          end
+          result
         end
       end
       @targets.each do |target, info|
-        next if targets_processed.include?(target)
-        unless process_target.call(target)
-          cache.write
-          raise BuildError.new("Failed to build #{target}")
-        end
+        process_target.call(target)
       end
       cache.write
     end

spec/rscons/environment_spec.rb

@@ -113,6 +113,20 @@ module Rscons
         env.process
       end
 
+      it "builds dependent targets first" do
+        env = Environment.new
+        env.Program("a.out", "main.o")
+        env.Object("main.o", "other.cc")
+
+        cache = "cache"
+        Cache.should_receive(:new).and_return(cache)
+        env.should_receive(:run_builder).with(anything, "main.o", ["other.cc"], cache, {}).and_return("main.o")
+        env.should_receive(:run_builder).with(anything, "a.out", ["main.o"], cache, {}).and_return("a.out")
+        cache.should_receive(:write)
+
+        env.process
+      end
+
       it "raises a BuildError when building fails" do
         env = Environment.new
         env.Program("a.out", "main.o")
@@ -123,7 +137,7 @@ module Rscons
         env.should_receive(:run_builder).with(anything, "main.o", ["other.cc"], cache, {}).and_return(false)
         cache.should_receive(:write)
 
-        expect { env.process }.to raise_error BuildError, /Failed.to.build.a\.out/
+        expect { env.process }.to raise_error BuildError, /Failed.to.build.main.o/
       end
     end