Download git binary on Windows or Linux if not found

TODO: test this on Windows

Author: tkelman

.gitignore

@@ -2,4 +2,5 @@
 *.jl.*.cov
 *.jl.mem
 deps/downloads/
+deps/usr/
 deps/deps.jl

deps/build.jl

@@ -1,27 +1,73 @@
 using Compat
-using BinDeps # just for download_cmd, unpack_cmd
 if is_apple()
     using Homebrew
 end
 
 gitcmd = `git`
-gitversion = "notfound"
+gitver = "notfound"
 try
-    gitversion = readchomp(`$gitcmd --version`)
+    gitver = readchomp(`$gitcmd --version`)
 end
-if gitversion == "notfound"
-    # TODO download it, or use homebrew's
-    gitversion = ""
-    downloadurl = ""
-    info("Downloading git version $gitversion from $downloadurl")
+if gitver == "notfound"
+    if is_apple()
+        # we could allow other options, but lots of other packages already
+        # depend on Homebrew.jl on mac and it needs a working git to function
+        error("Working git not found on path, try running\nPkg.build(\"Homebrew\")")
+    end
+    import BinDeps: download_cmd, unpack_cmd, splittarpath
+    baseurl = ""
+    filename = ""
+    if is_linux() && Sys.ARCH === :x86_64
+        # use conda for a non-root option
+        gitver = "2.8.2"
+        baseurl = "https://anaconda.org/conda-forge/git/$gitver/download/linux-64/"
+        filename = "git-$gitver-2.tar.bz2"
+    elseif is_linux() && (Sys.ARCH in (:i686, :i586, :i486, :i386))
+        # conda-forge doesn't build for 32 bit linux
+        gitver = "2.6.4"
+        baseurl = "https://anaconda.org/anaconda/git/$gitver/download/linux-32/"
+        filename = "git-$gitver-0.tar.bz2"
+    elseif is_windows()
+        # download and extract portablegit
+        gitver = "2.9.0"
+        baseurl = "https://github.com/git-for-windows/git/releases/" *
+            "download/v$gitver.windows.1/"
+        filename = "PortableGit-$gitver-$(Sys.WORD_SIZE)-bit.7z.exe"
+    end
+    downloadurl = baseurl * filename
+    if !isempty(downloadurl)
+        info("Downloading git version $gitver from $downloadurl\nTo " *
+            "avoid this download, install git manually and add it to your " *
+            "path before\nrunning Pkg.add(\"Git\") or Pkg.build(\"Git\")")
+        dest = joinpath("usr", string(Sys.MACHINE))
+        for dir in ("downloads", "usr", dest)
+            isdir(dir) || mkdir(dir)
+        end
+        filename = joinpath("downloads", filename)
+        isfile(filename) || run(download_cmd(downloadurl, filename))
+        # TODO: checksum validation
+        (b, ext, sec_ext) = splittarpath(filename)
+        run(unpack_cmd(filename, dest, ext, sec_ext))
+        gitcmd = `$(joinpath(dirname(@__FILE__), dest, "bin", "git"))`
+    end
+    try
+        gitver = readchomp(`$gitcmd --version`)
+        info("Successfully installed $gitver to $gitcmd")
+        # TODO: fix a warning about missing /templates here on linux
+        # by setting an environment variable in deps.jl
+    catch err
+        error("Could not automatically install git, error was: $err\n" *
+            (isempty(downloadurl) ? "Try installing git via your system " *
+            "package manager then running\nPkg.build(\"Git\")" : ""))
+    end
 else
     try
         # this is in a try because some environments like centos 7
         # docker containers don't have `which` installed by default
         gitpath = readchomp(is_windows() ? `where git` : `which git`)
         gitcmd = `$gitpath`
     end
-    info("Using $gitversion found on path" * (gitcmd == `git` ?
+    info("Using $gitver found on path" * (gitcmd == `git` ?
         "" : " at $gitcmd"))
 end
 open("deps.jl", "w") do f