add infrastructure for making releases

Idea: a release will be a git tag, distributed as an autogenerated
archive (eg. by GitLab release feature).
This version string must therefore be stored in a revisioned file, so we
use `.version` for this purpose. Before tagging a new release this file
will have to be updated with the new version number.

When building gray the revision (shown in the output headers and usage
screen) will be set to either

- the latest commit hash when building from a git checkout,

- from the .version file when building from release archive.

The implementation is based on whether the .git directory is present.

.version

@@ -0,0 +1 @@
+1.0.0

Makefile

@@ -53,15 +53,24 @@ MANPAGES  = $(addprefix $(SHAREDIR)/,gray.1 gray-convert.1 gray.ini.5 \
               profiles.txt.5 beamdata.txt.5 magneticdata.txt.5)
 
 ##
-## Git information (used in the version string)
+## Version information
 ##
 
+ifneq ($(wildcard .git/*),)
+# We are building from a git checkout
+
 # Short hash of the latest commit
-GIT_REV   ?= $(shell git rev-parse --short HEAD)
+GIT_REV ?= $(shell git rev-parse --short HEAD)
 
 # Whether the worktree and the latest commit differs
 GIT_DIRTY ?= $(shell test -n "$$(git status --porcelain)" && echo "-dirty")
 
+REVISION ?= $(GIT_REV)$(GIT_DIRTY)
+else
+# We are building from a release archive, use the version
+REVISION ?= v$(file < .version)
+endif
+
 # Source date
 ifndef SOURCE_DATE_EPOCH
 # Use current date
@@ -76,7 +85,7 @@ DATE=$(shell LC_TIME=C date -d @$(SOURCE_DATE_EPOCH) '+%B %Y')
 LD = $(FC)
 FFLAGS   += -I$(INCDIR) -fpic
 LDFLAGS  += -L$(LIBDIR)
-CPPFLAGS += -DREVISION=\"$(GIT_REV)$(GIT_DIRTY)\" -DPREFIX=\"$(PREFIX)\"
+CPPFLAGS += -DREVISION=\"$(REVISION)\" -DPREFIX=\"$(PREFIX)\"
 
 # Compiler-specific flags
 ifdef GNU

default.nix

@@ -14,18 +14,19 @@ let
     sha256 = "007nv11r0z9fz593iwzn55nc0p0wj5lpgf0k2brhs1ynmikq9gjr";
   };
 
-  # Exclude this file and build artifacts
+  # Exclude this file, build artifacts and git
   source = builtins.filterSource
     (path: type:
       !builtins.elem path [ "configure.mk" "default.nix" "result" ]
-      && baseNameOf path != "build") ./.;
+      && baseNameOf path != "build"
+      && baseNameOf path != ".git") ./.;
 
   inherit (import nixpkgs {}) lib pkgs;
 
 in
   pkgs.stdenv.mkDerivation rec {
     pname = "gray";
-    version = "0.1";
+    version = builtins.readFile ./.version;
     src = source;
 
     doCheck = true;
@@ -72,8 +73,6 @@ in
       (lib.enableFeature static "static")
       "--with-katex=${katex}"
       "--enable-deterministic"
-      "GIT_REV=${version}"
-      "GIT_DIRTY="
     ];
 
     meta = {