common/command: error if only/except points to bad build

CHANGELOG.md

 ## 0.3.5 (unreleased)
 
+BUG FIXES:
 
+* command/build,command/validate: If a non-existent build is specified to
+  '-only' or '-except', it is now an error. [GH-326]
 
 ## 0.3.4 (August 21, 2013)
 

common/command/template.go

@@ -65,6 +65,27 @@ func (f *BuildOptions) AllUserVars() (map[string]string, error) {
 // configured options.
 func (f *BuildOptions) Builds(t *packer.Template, cf *packer.ComponentFinder) ([]packer.Build, error) {
 	buildNames := t.BuildNames()
+
+	checks := make(map[string][]string)
+	checks["except"] = f.Except
+	checks["only"] = f.Only
+	for t, ns := range checks {
+		for _, n := range ns {
+			found := false
+			for _, actual := range buildNames {
+				if actual == n {
+					found = true
+					break
+				}
+			}
+
+			if !found {
+				return nil, fmt.Errorf(
+					"Unknown build in '%s' flag: %s", t, n)
+			}
+		}
+	}
+
 	builds := make([]packer.Build, 0, len(buildNames))
 	for _, buildName := range buildNames {
 		if len(f.Except) > 0 {

common/command/template_test.go

@@ -77,6 +77,26 @@ func TestBuildOptionsBuilds_only(t *testing.T) {
 	}
 }
 
+func TestBuildOptionsBuilds_exceptNonExistent(t *testing.T) {
+	opts := new(BuildOptions)
+	opts.Except = []string{"i-dont-exist"}
+
+	_, err := opts.Builds(testTemplate())
+	if err == nil {
+		t.Fatal("err should not be nil")
+	}
+}
+
+func TestBuildOptionsBuilds_onlyNonExistent(t *testing.T) {
+	opts := new(BuildOptions)
+	opts.Only = []string{"i-dont-exist"}
+
+	_, err := opts.Builds(testTemplate())
+	if err == nil {
+		t.Fatal("err should not be nil")
+	}
+}
+
 func TestBuildOptionsValidate(t *testing.T) {
 	bf := new(BuildOptions)