Kranc should output its directory and branch when it runs

[ianhinder]

Kranc should output its directory and branch when it runs. This should go to the screen, and probably also to the generated thorn's README or a small source file. This may help prevent surprises if people accidentally run the wrong version.

(Requested by Erik Schnetter in https://trac.einsteintoolkit.org/ticket/698)

[barrywardell]

I use the following piece of code to achieve this for another Mathematica package. It first checks for BUILD_ID and GIT_REVISION files (which are included in releases), and then falls back to detecting these manually.

KrancVersion[] :=
Module[{path, buildid, gitrev},
path = FileNameDrop[FindFile["Kranc`"], -2];

buildid = Quiet@ReadList[FileNameJoin[{path, "BUILD_ID"}], "String"];
If[SameQ[buildid, $Failed],
buildid = "git";
,
buildid = First[buildid];
];

gitrev = Quiet@ReadList[FileNameJoin[{path, "GIT_REVISION"}],"String"];
If[SameQ[gitrev, $Failed],
gitrev = First@ReadList["!git --git-dir "<>FileNameJoin[{path, ".git"}]<>" rev-parse HEAD", String];
,
gitrev = First[gitrev];
];

Grid[{{"Installed in:", path},
{"Build ID: ", buildid},
{"Git revision: ", gitrev}},
Alignment -> Left]
]