Improve version strings.

Have the abbreviated git hash appear in the version string when not
using a released version of pgloader.

README.md

@@ -30,6 +30,25 @@ The versioning is now following the Emacs model, where any X.0 release
 number means you're using a development version (alpha, beta, or release
 candidate). The next stable versions are going to be `3.1` then `3.2` etc.
 
+When using a development snapshot rather than a released version the version
+number includes the git hash (in its abbreviated form):
+
+  - `pgloader version "3.0.99"`
+  
+     Release candidate 9 for pgloader version 3.1, with a *git tag* named
+     `v3.0.99` so that it's easy to checkout the same sources as the
+     released code.
+     
+  - `pgloader version "3.0.fecae2c"`
+  
+     Development snapshot again *git hash* `fecae2c`. It's possible to have
+     the same sources on another setup with using the git command `git
+     checkout fecae2c`.
+
+  - `pgloader version "3.1.0"`
+  
+     Stable release.
+
 ## INSTALL
 
 pgloader is now a Common Lisp program, tested using the

src/params.lisp

@@ -32,7 +32,24 @@
 
 (in-package :pgloader.params)
 
-(defparameter *version-string* "3.0.99"
+(defparameter *release* nil
+  "non-nil when this build is a release build.")
+
+(defparameter *major-version* "3.0")
+(defparameter *minor-version* "99")
+
+(defun git-hash ()
+  "Return the current abbreviated git hash of the development tree."
+  (let ((git-hash `("git" "--no-pager" "log" "-n1" "--format=format:%h")))
+    (uiop:with-current-directory ((asdf:system-source-directory :pgloader))
+      (multiple-value-bind (stdout stderr code)
+          (uiop:run-program git-hash :output :string)
+        (declare (ignore code stderr))
+        stdout))))
+
+(defparameter *version-string*
+  (concatenate 'string *major-version* "."
+               (if *release* *minor-version* (git-hash)))
   "pgloader version strings, following Emacs versionning model.")
 
 ;; we can't use pgloader.utils:make-pgstate yet because params is compiled