Replace the ugly shell script into a awesome ocamlscript

We update src/core/opamGitVersion.ml only if the current git revision has really changed

Makefile

@@ -103,12 +103,9 @@ src/core/opamVersion.ml:
 	@echo
 	@exit 1
 
-.git/refs/heads/master:
-	mkdir -p .git/refs/heads/
-	touch $<
-
-src/core/opamGitVersion.ml: .git/HEAD
-	./shell/get-git-id.sh > $@
+.PHONY: src/core/opamGitVersion.ml
+src/core/opamGitVersion.ml:
+	ocaml shell/get-git-id.ml $@
 
 src/core/opamScript.ml: shell/ src/core/opamVersion.ml
 	ocaml shell/crunch.ml "complete"     < shell/opam_completion.sh > $@

shell/get-git-id.ml

@@ -0,0 +1,38 @@
+let file =
+  if Array.length Sys.argv <> 2 then (
+    Printf.eprintf "usage: ocaml %s <file>\n" Sys.argv.(0);
+    exit 1
+  ) else
+    Sys.argv.(1)
+
+let read file =
+  let ic = open_in_bin file in
+  input_line ic
+
+let write file contents =
+  let write () =
+    let oc = open_out file in
+    output_string oc contents;
+    output_char oc '\n';
+    close_out oc in
+  if Sys.file_exists file then (
+    let actual = read file in
+    if actual <> contents then write ()
+  ) else
+    write ()
+
+let (/) = Filename.concat
+
+let git file = ".git" / file
+
+let () =
+  let opamGitVersion = "src" / "core" / "opamGitVersion.ml" in
+  if Sys.file_exists (git "HEAD") then (
+    let reference =
+      let s = read (git "HEAD") in
+      let c = String.rindex s ' ' in
+      String.sub s (c+1) (String.length s -c-1) in
+    let sha1 = read (git reference) in
+    write opamGitVersion (Printf.sprintf "let version = Some %S" sha1)
+  ) else
+    write opamGitVersion "let version = None"