feat: guess whether command was invoked non-interactively

Previously, it was made possible to control the interactivity status of the
progress bar by setting `_G.interactive`. However, this was not
automatically inferred from the context the process was started from,
and was expected to be manually set by the library invoker.

Non-interactivity status is now inferred automatically based on the
context the command was called from.

toolchainlib/src/init.luau

@@ -30,6 +30,7 @@ local ProgressBar = require("./utils/progress")
 local compression = require("./compression")
 local eq = require("./utils/eq")
 local manifest = require("./manifest")
+local sys = require("./utils/sys")
 
 export type ToolId = {
 	alias: Option<string>,
@@ -165,8 +166,12 @@ local function getGithubToken(): Option<string>
 	end)
 end
 
+local function isInteractive(): boolean
+	return sys.isTTY("stdout") and process.env.TERM ~= "dumb" and process.env.CI == nil
+end
+
 -- Initialize the shared global progress bar state
-_G.interactive = nil
+_G.interactive = isInteractive() or nil
 local barFns
 
 function installTool(tool: ToolId, installPath: pathfs.Path): number

toolchainlib/src/utils/sys.luau

@@ -0,0 +1,52 @@
+--> Non-exhaustive set of util functions for Linux systems
+
+local process = require("@lune/process")
+
+local ResultExt = require("./ext/result")
+
+local fs = require("../../lune_packages/pathfs").fs
+local Result = require("../../lune_packages/result")
+local Option = require("../../lune_packages/option")
+
+local sys = {}
+sys.consts = {
+	S_IFMT = 0xF000,
+	S_IFCHR = 0x2000,
+}
+
+export type StdioFd = "stdin" | "stdout" | "stderr"
+local STDIO_FD_LOOKUP: { [StdioFd]: number } = {
+	stdin = 0,
+	stdout = 1,
+	stderr = 2,
+}
+
+function sys.isCharacterDevice(mode: number)
+	return bit32.band(mode, sys.consts.S_IFMT) == sys.consts.S_IFCHR
+end
+
+function sys.isTTY(fd: number | StdioFd): boolean
+	if process.os ~= "linux" then
+		-- idk about windows and macOS :p
+		return true
+	end
+
+	local inputFd: number = if typeof(fd) == "string" then STDIO_FD_LOOKUP[fd] else fd
+	local statFd = fs.readFile("/proc/self/stat")
+	local pid = assert(string.match(statFd, "^%S+%s+%S+%s+%S+%s+(%S+)"), "Could not get current process PID")
+
+	local stdoutFdMode = ResultExt.ok(
+		Result.try(process.spawn, "stat", { "-L", "-c", "%f", `/proc/{pid}/fd/{inputFd}` })
+	)
+		:andThen(function(child: process.SpawnResult)
+			if not child.ok then
+				return Option.None
+			end
+
+			return Option.from(tonumber(child.stdout, 16))
+		end)
+
+	return stdoutFdMode:isSomeAnd(sys.isCharacterDevice)
+end
+
+return sys