Make Nibbles work well both with ASDF 2.27 and with earlier versions.

Stop using the :if-component-dep-fails feature dropped in ASDF 2.27.
Instead use proper #+ read-time conditionals in the SBCL-only files.
This keeps all files tracked as part of the component tree.
Simplify some of the ASDF plumbing.

nibbles.asd

@@ -5,11 +5,8 @@
 
 (cl:in-package :nibbles-system)
 
-(defclass txt-file (asdf:doc-file) ())
-(defclass css-file (asdf:doc-file) ())
-
-(defmethod asdf:source-file-type ((c txt-file) (s asdf:module)) "txt")
-(defmethod asdf:source-file-type ((c css-file) (s asdf:module)) "css")
+(defclass txt-file (asdf:doc-file) ((type :initform "txt")))
+(defclass css-file (asdf:doc-file) ((type :initform "css")))
 
 (asdf:defsystem :nibbles
   :version "0.10"
@@ -30,27 +27,15 @@
 			 (:css-file "style")))
                (:module "sbcl-opt"
                         :depends-on ("package" "macro-utils")
-                        :if-component-dep-fails :ignore
-                        :components ((:file "fndb"
-                                            :in-order-to ((asdf:compile-op
-                                                           (asdf:feature :sbcl))))
+                        :components ((:file "fndb")
                                      (:file "nib-tran" :depends-on ("fndb"))
-                                     (:file "x86-vm"
-                                            :in-order-to ((asdf:compile-op (asdf:feature :x86))
-                                                          (asdf:compile-op (asdf:load-op "fndb"))))
-                                     (:file "x86-64-vm" :depends-on ("fndb")
-                                            :in-order-to ((asdf:compile-op (asdf:feature :x86-64))
-                                                          (asdf:compile-op (asdf:load-op "fndb"))))))))
+                                     (:file "x86-vm" :depends-on ("fndb"))
+                                     (:file "x86-64-vm" :depends-on ("fndb"))))))
 
 (defmethod asdf:perform ((op asdf:test-op)
                          (c (eql (asdf:find-system :nibbles))))
   (asdf:oos 'asdf:test-op 'nibbles-tests))
 
-;;; A tester's job is never done!
-(defmethod asdf:operation-done-p ((op asdf:test-op)
-                                  (c (eql (asdf:find-system :nibbles))))
-  nil)
-
 (asdf:defsystem :nibbles-tests
   :depends-on (:nibbles)
   :version "0.1"
@@ -60,10 +45,6 @@
   :components ((:file "rt")
                (:file "tests" :depends-on ("rt"))))
 
-(defmethod asdf:operation-done-p ((op asdf:test-op)
-                                  (c (eql (asdf:find-system :nibbles-tests))))
-  nil)
-
 (defmethod asdf:perform ((op asdf:test-op)
                          (c (eql (asdf:find-system :nibbles-tests))))
   (or (funcall (intern "DO-TESTS" (find-package "RTEST")))

sbcl-opt/fndb.lisp

@@ -2,6 +2,8 @@
 
 (cl:in-package :nibbles)
 
+#+sbcl (progn
+
 ;;; Efficient array bounds checking
 (sb-c:defknown %check-bound
   ((simple-array (unsigned-byte 8) (*)) index (and fixnum sb-vm:word)
@@ -39,3 +41,5 @@
                      ,internal-arg-types
                      ,arg-type) into defknowns
         finally (return `(progn ,@defknowns)))
+
+);#+sbcl

sbcl-opt/nib-tran.lisp

@@ -2,6 +2,8 @@
 
 (cl:in-package :nibbles)
 
+#+sbcl (progn
+
 (sb-c:deftransform %check-bound ((vector bound offset n-bytes)
 				 ((simple-array (unsigned-byte 8) (*)) index
 				  (and fixnum sb-vm:word)
@@ -95,3 +97,5 @@
           else if (<= bitsize sb-vm:n-word-bits)
             collect generic-little-transform into transforms
           finally (return `(progn ,@transforms))))
+
+);#+sbcl

sbcl-opt/x86-64-vm.lisp

@@ -1,7 +1,10 @@
 ;;;; x86-64-vm.lisp -- VOP definitions SBCL
 
+#+sbcl
 (cl:in-package :sb-vm)
 
+#+(and sbcl x86-64) (progn
+
 (define-vop (%check-bound)
   (:translate nibbles::%check-bound)
   (:policy :fast-safe)
@@ -113,3 +116,5 @@
           for big-endian-p = (logbitp 0 i)
           collect (frob bitsize setterp signedp big-endian-p) into forms
           finally (return `(progn ,@forms))))
+
+);#+(and sbcl x86-64)

sbcl-opt/x86-vm.lisp

@@ -1,7 +1,10 @@
 ;;;; x86-vm.lisp -- VOP definitions for SBCL
 
+#+sbcl
 (cl:in-package :sb-vm)
 
+#+(and sbcl x86) (progn
+
 (define-vop (%check-bound)
   (:translate nibbles::%check-bound)
   (:policy :fast-safe)
@@ -158,3 +161,5 @@
           for big-endian-p = (logbitp 0 i)
           collect (frob setterp signedp big-endian-p) into forms
           finally (return `(progn ,@forms))))
+
+);#+(and sbcl x86)