Adds a new --std-path argument to set standard library path.

This PR adds an `--std-path` argument to set standard library path as an
alternative to setting the `HAXE_STD_PATH` environment variable.

This is useful to be able to use Haxe from the ninja build system,
as it does not support setting environment variables from its build
scripts: ninja-build/ninja#1002

src/compiler/args.ml

@@ -126,6 +126,9 @@ let parse_args com =
 		("Compilation",[],["-libcp"],Arg.String (fun path ->
 			com.class_paths#add (new ClassPath.directory_class_path (Path.add_trailing_slash path) Lib);
 		),"<path>","add a directory to find source files");
+		("Compilation",["--std-path"],["-std-path"],Arg.String (fun path ->
+			com.std_path <- path;
+		),"<path>","set the path of the standard library");
 		("Compilation",["--hxb-lib"],["-hxb-lib"],Arg.String (fun file ->
 			let lib = create_native_lib file false HxbLib in
 			actx.hxb_libs <- lib :: actx.hxb_libs

src/compiler/compiler.ml

@@ -154,7 +154,7 @@ module Setup = struct
 					let hl_ver = try
 						Std.input_file (Common.find_file com "hl/hl_version")
 					with Not_found ->
-						failwith "The file hl_version could not be found. Please make sure HAXE_STD_PATH is set to the standard library corresponding to the used compiler version."
+						failwith "The file hl_version could not be found. Please make sure `HAXE_STD_PATH` environment variable or `--std-path` argument is set to the standard library corresponding to the used compiler version."
 					in
 					Define.define_value com.defines Define.HlVer hl_ver
 				end;
@@ -187,9 +187,9 @@ module Setup = struct
 
 	open ClassPath
 
-	let get_std_class_paths () =
+	let get_std_class_paths std_path =
 		try
-			let p = Sys.getenv "HAXE_STD_PATH" in
+			let p = if std_path = "" then Sys.getenv "HAXE_STD_PATH" else std_path in
 			let p = Path.remove_trailing_slash p in
 			let rec loop = function
 				| drive :: path :: l ->
@@ -224,7 +224,7 @@ module Setup = struct
 				let cp = new ClassPath.directory_class_path (Path.add_trailing_slash s) scope in
 				com.class_paths#add cp
 			with Sys_error _ -> ()
-		) (List.rev (get_std_class_paths ()));
+		) (List.rev (get_std_class_paths com.std_path));
 		com.class_paths#add com.empty_class_path
 
 	let setup_common_context ctx =

src/context/common.ml

@@ -369,6 +369,7 @@ type context = {
 	mutable foptimize : bool;
 	mutable platform : platform;
 	mutable config : platform_config;
+	mutable std_path : string;
 	empty_class_path : ClassPath.class_path;
 	class_paths : ClassPaths.class_paths;
 	main : context_main;
@@ -793,6 +794,7 @@ let create compilation_step cs version args display_mode =
 		print = (fun s -> print_string s; flush stdout);
 		run_command = Sys.command;
 		run_command_args = (fun s args -> com.run_command (Printf.sprintf "%s %s" s (String.concat " " args)));
+		std_path = "";
 		empty_class_path = new ClassPath.directory_class_path "" User;
 		class_paths = new ClassPaths.class_paths;
 		main = {

src/core/error.ml

@@ -328,12 +328,12 @@ let raise_msg ?(depth = 0) msg p = raise_error_msg ~depth (Custom msg) p
 let raise_typing_error ?(depth = 0) msg p = raise_msg ~depth msg p
 let raise_typing_error_ext err = raise_error err
 
-let raise_std_not_found () =
+let raise_std_not_found std_path =
 	try
-		let std_path = Sys.getenv "HAXE_STD_PATH" in
-		raise_typing_error ("Standard library not found. Please check your `HAXE_STD_PATH` environment variable (current value: \"" ^ std_path ^ "\")") null_pos
+		let std_path = if std_path = "" then Sys.getenv "HAXE_STD_PATH" else std_path in
+		raise_typing_error ("Standard library not found. Please check your `HAXE_STD_PATH` environment variable or `--std-path` argument (current value: \"" ^ std_path ^ "\")") null_pos
 	with Not_found ->
-		raise_typing_error "Standard library not found. You may need to set your `HAXE_STD_PATH` environment variable" null_pos
+		raise_typing_error "Standard library not found. You may need to set your `HAXE_STD_PATH` environment variable or pass a `--std-path` argument" null_pos
 
 let error_require r p =
 	if r = "" then

src/typing/macroContext.ml

@@ -722,7 +722,7 @@ let create_macro_context com =
 	(* This can run before `TyperEntry.create`, so in order to display nice error when std is not found, this needs to be checked here too *)
 	(match !eval_std with
 	| Some std -> com2.class_paths#add std
-	| None -> Error.raise_std_not_found ());
+	| None -> Error.raise_std_not_found com.std_path);
 	let defines = adapt_defines_to_macro_context com2.defines; in
 	com2.defines.values <- defines.values;
 	com2.defines.defines_signature <- None;

src/typing/typerEntry.ml

@@ -63,7 +63,7 @@ let create com macros =
 		TypeloadModule.load_module ctx ([],"StdTypes") null_pos
 	with
 		Error { err_message = Module_not_found ([],"StdTypes") } ->
-			Error.raise_std_not_found ()
+			Error.raise_std_not_found com.std_path
 	);
 	(* We always want core types to be available so we add them as default imports (issue #1904 and #3131). *)
 	List.iter (fun mt ->