Blam — Better Lua assert messages

blam file.lua file.luau directory

What?

Replaces nonexistent or empty string message arguments of Lua assert calls with the expression being asserted. assert(jump()) becomes assert(jump(), "[blam]\njump()"). Compatible with Lua 5.1, Lua 5.2, Lua 5.3, Lua 5.4, and Luau.

Caveat

For cases where the assertion expression returns multiple values, like assert(io.open("file")), the error message returned by io.open would be dropped when Blam adds its own message argument. To avoid this, store the returns as variables and pass them to assert.

local file, message = io.open("file")
assert(file, message)

Why?

Often assert messages are meant for developers, not users. assert(#inventory > 0) is about as clear to someone who knows Lua as assert(#inventory > 0, "inventory is empty"). But the default assertion failed! message is useful to nobody, and forces developers to open the file to figure out what's being asserted, even if once they know the assertion, the problem is obviously elsewhere.

assert is even more commonly useful in Luau, where it's used to refine types.

Blam also quiets Selene warnings for assert calls without a message argument.