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Update lint.md (#3)

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Document new FormatString lint
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Arseny Kapoulkine 2020-07-31 20:55:35 -07:00 committed by GitHub
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@ -200,3 +200,19 @@ end
## LocalShadowPedantic (17)
This warning extends `LocalShadow` by also warning about cases where a local variable shadows a local variable with the same name from a parent function, or when it shadows a builtin global. This warning tends to be noisy and as such is disabled by default.
## FormatString (18)
Luau has several library functions that expect a format string that specifies the behavior for the function. These format strings follow a specific syntax that depends on the question; mistakes in these strings can lead to runtime errors or unexpected behavior of the code.
To help make sure that the strings used for these functions are correct, linter checks calls to `string.format`, `string.pack`, `string.packsize`, `string.unpack`, `string.match`, `string.gmatch`, `string.find`, `string.gsub` and `os.date` and issues warnings when the call uses a literal string with an incorrect format:
```lua
-- Invalid match pattern: invalid capture reference, must refer to a closed capture
local cap = string.match(s, "(%d)%2")
-- Invalid format string: unfinished format specifier
local str = ("%d %"):format(1, 2)
```
Note that with the exception of `string.format` this only works when the function is called via the library, not via the method call (so prefer `string.match(s, "pattern")` to `s:match("pattern")`).