build: new utility for caching build configs.

* config-cache-hook.tl: New file. If this is is installed
as a git post-checkout hook, it will save and restore
the configuration materials, associated with commit hash,
under a directory called .config-cache. A cache of configs
covering a wide range of commits helps with git bisecting.

1 files changed, 34 insertions, 0 deletions

diff --git a/config-cache-hook.tl b/config-cache-hook.tl
new file mode 100755
index 00000000..73b7e30b
--- /dev/null
+++ b/config-cache-hook.tl
@@ -0,0 +1,34 @@
+#!txr --lisp
+
+;;
+;; This program is intended to be installed as .git/hooks/post-checkout.
+;; It caches the build configuration for the current commit, and restores
+;; it for the new commit, if possible.
+;;
+
+;; People have git hook directories which are shared among different
+;; repos; we only want to fire for txr.
+(unless (ends-with "txr" (pwd))
+  (exit))
+
+(defvarl %files% '#"reconfigure config.h config.make")
+(defvarl %cachedir% ".config-cache")
+
+(defun try-save-current-config (sha)
+  (when [all %files% path-exists-p]
+    (let ((dir (path-cat %cachedir% sha)))
+      (ensure-dir dir)
+      (copy-files %files% dir))))
+
+(defun try-restore-new-config (sha)
+  (let* ((dir (path-cat %cachedir% sha))
+         (files [map (op path-cat dir) %files%]))
+    (when [all files path-exists-p]
+      (copy-files files ".")
+      (put-line `restored cached configuration for @sha`))))
+
+(match-case *args*
+  (@(require (@prevsha @newsha @nil) 
+             (nequal prevsha newsha))
+   (try-save-current-config prevsha)
+   (try-restore-new-config newsha)))