`string.format` does not support precision specifiers (`%.2f`, `%05d`, etc.)

[davydog187]

Severity: Medium
Area: Standard library — lib/lua/vm/stdlib/string.ex

Description

string.format raises "bad argument to 'string.format' (invalid option '%.')" when given format specifiers with precision (e.g., %.2f) or width-and-precision combinations. Standard Lua 5.3/5.4 supports the full C printf-style format string syntax.

Reproduction

return string.format("%.2f", 3.14159)
-- Expected: "3.14"
-- Actual: ** (Lua.RuntimeException) bad argument to 'string.format' (invalid option '%.')

Workaround

Use %f (full float) or convert manually with math.floor / string concatenation.

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Summary Table

#	Bug	Severity	Status
1	local function declarations silently dropped	High	Open
2	function Table.method() dot-syntax fails at runtime	High	Open
3	Multiple for loops with the same variable name corrupt register allocation	High	Open
4	Register overlap in nested functions causes infinite for loops	Critical	Fixed
5	string.format does not support precision specifiers	Medium	Open