add Environment#depends() to specify user dependencies for a build target

lib/rscons/environment.rb

@@ -26,6 +26,7 @@ module Rscons
     def initialize(options = {})
       @varset = VarSet.new
       @targets = {}
+      @user_deps = {}
       @builders = {}
       @build_dirs = []
       @build_hooks = []
@@ -147,7 +148,7 @@ module Rscons
           result = run_builder(@targets[target][:builder],
                                target,
                                @targets[target][:source],
-                               [],
+                               @user_deps[target] || [],
                                cache,
                                @targets[target][:vars] || {})
           unless result
@@ -221,6 +222,13 @@ module Rscons
       end
     end
 
+    # Manually record a given target as depending on the specified
+    # dependency files.
+    def depends(target, *user_deps)
+      @user_deps[target] ||= []
+      @user_deps[target] = (@user_deps[target] + user_deps).uniq
+    end
+
     # Build a list of source files into files containing one of the suffixes
     # given by suffixes.
     # This method is used internally by RScons builders.

spec/build_tests_spec.rb

@@ -328,6 +328,37 @@ EOF
     ]
   end
 
+  it 'rebuilds when user-specified dependencies change' do
+    test_dir('simple')
+    Rscons::Environment.new do |env|
+      env.Program('simple', Dir['*.c'])
+      File.open("file.ld", "w") do |fh|
+        fh.puts("foo")
+      end
+      env.depends('simple', 'file.ld')
+    end
+    lines.should == ["CC simple.o", "LD simple"]
+    File.exists?('simple.o').should be_true
+    `./simple`.should == "This is a simple C program\n"
+    Rscons::Environment.new do |env|
+      env.Program('simple', Dir['*.c'])
+      File.open("file.ld", "w") do |fh|
+        fh.puts("bar")
+      end
+      env.depends('simple', 'file.ld')
+    end
+    lines.should == ["LD simple"]
+    Rscons::Environment.new do |env|
+      env.Program('simple', Dir['*.c'])
+      File.unlink("file.ld")
+    end
+    lines.should == ["LD simple"]
+    Rscons::Environment.new do |env|
+      env.Program('simple', Dir['*.c'])
+    end
+    lines.should == []
+  end
+
   unless ENV["omit_gdc_tests"]
     it "supports building D sources" do
       test_dir("d")

spec/rscons/environment_spec.rb

@@ -230,6 +230,20 @@ module Rscons
       end
     end
 
+    describe "#depends" do
+      it "records the given dependencies in @user_deps" do
+        env = Environment.new
+        env.depends("foo", "bar", "baz")
+        env.instance_variable_get(:@user_deps).should == {"foo" => ["bar", "baz"]}
+      end
+      it "records user dependencies only once" do
+        env = Environment.new
+        env.instance_variable_set(:@user_deps, {"foo" => ["bar"]})
+        env.depends("foo", "bar", "baz")
+        env.instance_variable_get(:@user_deps).should == {"foo" => ["bar", "baz"]}
+      end
+    end
+
     describe "#build_sources" do
       class ABuilder < Builder
         def produces?(target, source, env)