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warnings.txt
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List of warnings
================
Warnings produced by Luacheck are categorized using three-digit warning codes.
Warning codes can be displayed in CLI output using "--codes" CLI option or
"codes" config option. Errors also have codes starting with zero; unlike
warnings, they can not be ignored.
==== =========================================================================
Code Description
==== =========================================================================
011 A syntax error.
021 An invalid inline option.
022 An unpaired inline push directive.
023 An unpaired inline pop directive.
111 Setting an undefined global variable.
112 Mutating an undefined global variable.
113 Accessing an undefined global variable.
121 Setting a read-only global variable.
122 Setting a read-only field of a global variable.
131 Unused implicitly defined global variable.
142 Setting an undefined field of a global variable.
143 Accessing an undefined field of a global variable.
211 Unused local variable.
212 Unused argument.
213 Unused loop variable.
221 Local variable is accessed but never set.
231 Local variable is set but never accessed.
232 An argument is set but never accessed.
233 Loop variable is set but never accessed.
241 Local variable is mutated but never accessed.
311 Value assigned to a local variable is unused.
312 Value of an argument is unused.
313 Value of a loop variable is unused.
314 Value of a field in a table literal is unused.
321 Accessing uninitialized local variable.
331 Value assigned to a local variable is mutated but never accessed.
341 Mutating uninitialized local variable.
411 Redefining a local variable.
412 Redefining an argument.
413 Redefining a loop variable.
421 Shadowing a local variable.
422 Shadowing an argument.
423 Shadowing a loop variable.
431 Shadowing an upvalue.
432 Shadowing an upvalue argument.
433 Shadowing an upvalue loop variable.
511 Unreachable code.
512 Loop can be executed at most once.
521 Unused label.
531 Left-hand side of an assignment is too short.
532 Left-hand side of an assignment is too long.
541 An empty "do" "end" block.
542 An empty "if" branch.
551 An empty statement.
561 Cyclomatic complexity of a function is too high.
571 A numeric for loop goes from #(expr) down to 1 or less without negative
step.
611 A line consists of nothing but whitespace.
612 A line contains trailing whitespace.
613 Trailing whitespace in a string.
614 Trailing whitespace in a comment.
621 Inconsistent indentation ("SPACE" followed by "TAB").
631 Line is too long.
==== =========================================================================
Global variables (1xx)
----------------------
For each file, Luacheck builds list of defined globals and fields which can be
used there. By default only globals from Lua standard library are defined;
custom globals can be added using "--globals" CLI option or "globals" config
option, and version of standard library can be selected using "--std" CLI
option or "std" config option. When an undefined global or field is set,
mutated or accessed, Luacheck produces a warning.
Read-only globals
By default, most standard globals and fields are marked as read-only, so that
setting them produces a warning. Custom read-only globals and fields can be
added using "--read-globals" CLI option or "read_globals" config option, or
using a custom set of globals. See "custom_stds"
Globals and fields that are not read-only by default:
* "_G"
* "_ENV" (treated as a global by Luacheck)
* "package.path"
* "package.cpath"
* "package.loaded"
* "package.preload"
* "package.loaders"
* "package.searchers"
Implicitly defined globals
Luacheck can be configured to consider globals assigned under some conditions
to be defined implicitly. When "-d"/"--allow_defined" CLI option or
"allow_defined" config option is used, all assignments to globals define them;
when "-t"/"--allow_defined_top" CLI option or "allow_defined_top" config
option is used, assignments to globals in the top level function scope (also
known as main chunk) define them. A warning is produced when an implicitly
defined global is not accessed anywhere.
Modules
Files can be marked as modules using "-m"/"--module" CLI option or "module"
config option to simulate semantics of the deprecated "module"
http://www.lua.org/manual/5.1/manual.html#pdf-module function. Globals
implicitly defined inside a module are considired part of its interface, are
not visible outside and are not reported as unused. Assignments to other
globals are not allowed, even to defined ones.
Unused variables (2xx) and values (3xx)
---------------------------------------
Luacheck generates warnings for all unused local variables except one named
"_". It also detects variables which are set but never accessed or accessed
but never set.
Unused values and uninitialized variables
For each value assigned to a local variable, Luacheck computes set of
expressions where it could be used. Warnings are produced for unused values
(when a value can't be used anywhere) and for accessing uninitialized
variables (when no values can reach an expression). E.g. in the following
snippet value assigned to "foo" on line 1 is unused, and variable "bar" is
uninitialized on line 9:
local foo = expr1()
local bar
if condition() then
foo = expr2()
bar = expr3()
else
foo = expr4()
print(bar)
end
return foo, bar
Secondary values and variables
Unused value assigned to a local variable is secondary if its origin is the
last item on the RHS of assignment, and another value from that item is used.
Secondary values typically appear when result of a function call is put into
locals, and only some of them are later used. For example, here value assigned
to "b" is secondary, value assigned to "c" is used, and value assigned to "a"
is simply unused:
local a, b, c = f(), g()
return c
A variable is secondary if all values assigned to it are secondary. In the
snippet above, "b" is a secondary variable.
Warnings related to unused secondary values and variables can be removed using
"-s"/"--no-unused-secondaries" CLI option or "unused_secondaries" config
option.
Shadowing declarations (4xx)
----------------------------
Luacheck detects declarations of local variables shadowing previous
declarations, unless the variable is named "_". If the previous declaration is
in the same scope as the new one, it is called redefining.
Note that it is not necessary to define a new local variable when
overwriting an argument:
local function f(x)
local x = x or "default" -- bad
end
local function f(x)
x = x or "default" -- good
end
Control flow and data flow issues (5xx)
---------------------------------------
Unreachable code
Luacheck detects unreachable code. It also detects it if end of a loop block
is unreachable, which means that the loop can be executed at most once:
for i = 1, 100 do
-- Break statement is outside the "if" block,
-- so that the loop always stops after the first iteration.
if cond(i) then f() end break
end
Unused labels
Labels that are not used by any "goto" statements are reported as unused.
Unbalanced assignments
If an assignment has left side and right side with different lengths, the
assignment is unbalanced and Luacheck warns about it.
An exception is initializing several local variables in a single statement
while leaving some uninitialized:
local a, b, c = nil -- Effectively sets "a", "b", and "c" to nil, no warning.
Empty blocks
Luacheck warns about empty "do" "end" blocks and empty "if" branches ("then"
"else", "then" "elseif", and "then" "end").
Empty statements
In Lua 5.2+ semicolons are considered statements and can appear even when not
following normal statements. Such semicolons produce Luacheck warnings as they
are completely useless.
Cyclomatic complexity
If a limit is set using "--max-cyclomatic-complexity" CLI option or
corresponding config or inline options, Luacheck warns about functions with
too high cyclomatic complexity.
Reversed numeric for loops
Iterating a table in reverse using a numeric for loop going from "#t" to "1"
requires a negative loop step. Luacheck warns about loops going from "#(some
expression)" to "1" or a smaller constant when the loop step is not negative:
-- Warning for this loop:
-- numeric for loop goes from #(expr) down to 1 but loop step is not
-- negative
for i = #t, 1 do
print(t[i])
end
-- This loop is okay.
for i = #t, 1, -1 do
print(t[i])
end
Formatting issues (6xx)
-----------------------
Whitespace issues
Luacheck warns about trailing whitespace and inconsistent indentation ("SPACE"
followed by "TAB").
Some examples of trailing whitespace Luacheck finds:
-- Whitespace example.
print("Hello")
print("World")
Here:
* Any tabs or spaces after either ")" would be considered trailing.
* Any tabs or spaces after the "." in the comment would be considered
trailing
* Any tabs or spaces on the empty line between the two "print" statements
would also be considered a form of trailing whitespace.
Trailing whitespace in any of these forms is useless, can be a nuisance to
developers navigating around a file, and is forbidden in many formatting
styles.
Line length limits
Luacheck warns about lines that are longer then some limit. Default limit is
"120" characters. It's possible to change this limit using "--max-line-length"
CLI option or disable the check completely with "--no-max-line-length"; there
are similar config and inline options.
Additionally, separate limits can be set for three different type of lines:
* "String" lines have their line ending inside a string, typically a long
string using "[[...]]" syntax.
* "Comment" lines have their line ending inside a long comment ("--[[...]]"),
or end with a short comment using normal "--..." syntax.
* "Code" lines are all other lines.
These types of lines are limited using CLI options named
"--[no-]max-string-line-length", "--[no-]max-comment-line-length", and
"--[no-]max-code-line-length", with similar config and inline options.