Specify length of git hash prefix used in build info version

fix #4855

Signed-off-by: Josh Berdine <josh@berdine.net>

Author: jberdine

bin/subst.ml

@@ -26,12 +26,12 @@ let man =
      ^ {|) strings by the version obtained from the vcs. Currently only git is
             supported and the version is obtained from the output of:|}
       )
-  ; `Pre {|  \$ git describe --always --dirty|}
+  ; `Pre {|  \$ git describe --always --dirty --abbrev=7|}
   ; `P
       {|$(b,dune subst) substitutes the variables that topkg substitutes with
           the default configuration:|}
   ; var "NAME" "the name of the project (from the dune-project file)"
-  ; var "VERSION" "output of $(b,git describe --always --dirty)"
+  ; var "VERSION" "output of $(b,git describe --always --dirty --abbrev=7)"
   ; var "VERSION_NUM"
       ("same as $(b," ^ literal_version
      ^ ") but with a potential leading 'v' or 'V' dropped")

boot/duneboot.ml

@@ -697,7 +697,8 @@ module Build_info = struct
       if not (Sys.file_exists ".git") then
         Fiber.return None
       else
-        Process.try_run_and_capture "git" [ "describe"; "--always"; "--dirty" ]
+        Process.try_run_and_capture "git"
+          [ "describe"; "--always"; "--dirty"; "--abbrev=7" ]
         >>| function
         | Some s -> Some (String.trim s)
         | None -> None)

doc/dune-libs.rst

@@ -152,7 +152,7 @@ repositories:
 
 .. code:: bash
 
-          git describe --always --dirty
+          git describe --always --dirty --abbrev=7
 
 which produces a human readable version string of the form
 ``<version>-<commits-since-version>-<hash>[-dirty]``.

doc/usage.rst

@@ -418,7 +418,7 @@ git, dune-release invokes this command to find out the version:
 
 .. code:: bash
 
-    $ git describe --always --dirty
+    $ git describe --always --dirty --abbrev=7
     1.0+beta9-79-g29e9b37
 
 Projects using dune usually only need dune-release for creating and
@@ -434,7 +434,7 @@ project.
 More precisely, it replaces all the following watermarks in source files:
 
 - ``NAME``, the name of the project
-- ``VERSION``, output of ``git describe --always --dirty``
+- ``VERSION``, output of ``git describe --always --dirty --abbrev=7``
 - ``VERSION_NUM``, same as ``VERSION`` but with a potential leading
   ``v`` or ``V`` dropped
 - ``VCS_COMMIT_ID``, commit hash from the vcs

src/dune_engine/vcs.ml

@@ -116,7 +116,8 @@ let make_fun name ~git ~hg =
 let describe =
   Staged.unstage
   @@ make_fun "vcs-describe"
-       ~git:(fun t -> run_git t [ "describe"; "--always"; "--dirty" ])
+       ~git:(fun t ->
+         run_git t [ "describe"; "--always"; "--dirty"; "--abbrev=7" ])
        ~hg:(fun x ->
          let open Fiber.O in
          let+ res = hg_describe x in