Lint

Each lint has these levels:

• "allow" - don't report problems
• "hint" - report problems as slight tips
• "warning" - report problems as warnings
• "deny" - report problems as errors

unused

default: "warning"

This lint reports unused items, such as functions, globals, types, and even function parameters and locals. For WasmGC, fields in struct type are also supported.

Here is an example of unused functions and globals with or without identifiers:

(module
  (func)
  (func $f)
  (global i32
    i32.const 0)
  (global $g i32
    i32.const 0))

Sometimes, there may be unused items but you want to ignore them intentionally, then you can add an underscore prefix to the identifier:

(module
  (func $_)
  (func $_f))

So they won't be reported as unused.

shadow

default: "warning"

WebAssembly allows shadowing identifiers in block labels. For example:

(module
  (func
    (block $label
      (block $label
        br $label))))

However, it's confusing that you may want to jump to the label at line 3 or line 4. This lint reports such cases when you accidentally give the same name to different block labels.

implicitModule

default: "allow"

WABT allows defining module fields without the outer (module) syntax:

(func)
(global i32
  i32.const 0)

However, you may hope it to be more explicit, or your compiler doesn't support this syntax. In such cases, you can set this lint to "warning" or "deny".

multiModules

default: "deny"

Most compilers (such as WABT) only allow one module in a file.

(module)
(module)

If this doesn't match your needs, you can set this lint to "allow".

unreachable

default: "hint"

This lint reports unreachable code, for example those code after br, return and unreachable instructions or infinite loops:

(module
  (func
    (loop
      br 0)
    nop)
  (func
    return
    nop))

needlessMut

default: "warning"

This lint reports mutable items that are never mutated:

(module
  (global (mut i32)
    i32.const 0)
  (func (result i32)
    global.get 0))

For WasmGC, fields in struct type and array type is also supported:

(module
  (type $array (array (mut i32)))
  (type $struct (struct (field (mut i32))))
  (func (param (ref $array) (ref $struct)) (result i32 i32)
    local.get 0
    i32.const 0
    array.get $array
    local.get 1
    struct.get $struct 0))

multiMemories

default: "allow"

WebAssembly Language Tools supports Multiple Memories proposal by default:

(module
  (memory 1)
  (memory 2))

If your compiler or environment doesn't support this proposal, you can set this lint to "deny".