Add git integration.

Author: Jarod42

src/_premake_init.lua

@@ -564,6 +564,17 @@
 		kind = "boolean"
 	}
 
+	api.register {
+		name = "gitintegration",
+		scope = "global",
+		kind = "string",
+		allowed = {
+			"Off",
+			"Always",
+			"OnNewFiles"
+		}
+	}
+
 	api.register {
 		name = "inlining",
 		scope = "config",

src/_premake_main.lua

@@ -333,6 +333,62 @@
 		end
 	end
 
+---
+-- Run non-action generation part.
+---
+	local function find_git_root(current_path)
+		current_path = path.getabsolute(current_path or _MAIN_SCRIPT_DIR)
+	
+		while not os.isdir(path.join(current_path, ".git")) do
+			current_path = path.getdirectory(current_path)
+			if current_path == "" then
+				error("No git root path")
+			end
+		end
+		return current_path
+	end
+
+	local function print_git_post_checkout_hooks(root_path, mode)
+		local args = {}
+		for _, arg in ipairs(_ARGV) do
+			if not (arg:startswith("--file") or arg:startswith("/file")) then
+				table.insert(args, arg);
+			end
+		end
+
+		local indent = ''
+		p.outln('#!bin/sh')
+		if mode == 'OnNewFiles' then
+			p.outln('count=`git diff --compact-summary $1 $2 | grep -E "( \\(new\\)| \\(gone\\)|premake)" | wc -l`')
+			p.outln('if [ $count -ne 0 ]')
+			p.outln('then')
+			indent = '    '
+		end
+		p.outln(indent .. p.esc(path.getrelative(root_path, _PREMAKE_COMMAND)) .. ' --file=' .. p.esc(path.getrelative(root_path, _MAIN_SCRIPT)) .. ' ' .. table.concat(p.esc(args), ' '))
+		if mode == 'OnNewFiles' then
+			p.outln('fi')
+		end
+	end
+
+	function m.nonActionGeneration()
+		local git_integration_mode = p.api.rootContainer().gitintegration or "Off"
+		if git_integration_mode == "Off" then
+			return
+		end
+		local root_path = find_git_root()
+	
+		local content = p.capture(function () print_git_post_checkout_hooks(root_path, git_integration_mode) end)
+		local res, err = os.writefile_ifnotequal(content, path.join(root_path, '.git', 'hooks', 'post-checkout'))
+
+		if (res == 0) then -- file not modified
+			return
+		elseif (res < 0) then
+			error(err, 0)
+		elseif (res > 0) then -- file modified
+			printf("Generated %s...", path.getrelative(os.getcwd(), path.join(root_path, '.git', 'hooks', 'post-checkout')))
+			return
+		end
+	end
 
 ---
 -- Override point, for logic that should run after validation and
@@ -387,6 +443,7 @@
 		m.bake,
 		m.postBake,
 		m.validate,
+		m.nonActionGeneration,
 		m.preAction,
 		m.callAction,
 		m.postAction,

website/docs/gitintegration.md

@@ -0,0 +1,66 @@
+Enable git integration to run premake on checkout.
+
+```lua
+gitintegration ("value")
+```
+
+### Parameters ###
+
+| Action          | Description                                                                      |
+|-----------------|----------------------------------------------------------------------------------|
+| Off             | Disable git integration.                                                         |
+| Always          | Run premake on checkout.                                                         |
+| OnNewFiles      | Run premake only when files are added/removed or if premake script has changed.  |
+
+### Applies To ###
+
+Global scope.
+
+### Availability ###
+
+Premake 5.0.0 beta 3 or later for Visual Studio 2019 and later.
+
+### Examples ###
+
+Regenerate autoversion.h with git tag when checkout to another branch.
+
+```lua
+gitintegration "Always"
+
+local locationDir = _OPTIONS["to"]
+
+local function autoversion_h()
+	local git_tag, errorCode = os.outputof("git describe --tag --always")
+	if errorCode == 0 then
+		print("git description: ", git_tag)
+		local content = io.readfile("src/autoversion.h.in")
+		content = content:gsub("${GIT_DESC}", git_tag)
+
+		os.mkdir(locationDir)
+		local f, err = os.writefile_ifnotequal(content, path.join(locationDir, "autoversion.h"))
+
+		if (f == 0) then -- file not modified
+		elseif (f < 0) then
+			error(err, 0)
+			return false
+		elseif (f > 0) then
+			print("Generated autoversion.h...")
+		end
+
+		return true
+	else
+		print("`git describe --tag` failed with error code", errorCode, git_tag)
+		return false
+	end
+end
+
+local have_autoversion_h = autoversion_h()
+
+workspace "MyProject"
+	location(locationDir)
+
+	if have_autoversion_h then
+		includedirs { locationDir } -- for generated file (autoversion.h)
+	end
+  -- [..]
+```

website/sidebars.js

@@ -307,6 +307,14 @@ module.exports = {
 						'xcodesystemcapabilities'
 					]
 				},
+				{
+					collapsed: true,
+					type: 'category',
+					label: 'Global Settings',
+					items: [
+						gitintegration
+					]
+				},
 				{
 					collapsed: true,
 					type: 'category',