feat(lint): add empty-block detector#15540
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Flags a regular function whose body is empty, which is dead or unfinished code. Constructors, receive/fallback, virtual functions (extension hooks) and payable functions (ether sinks) are exempt: their empty body is the behavior. Functions without a body never fire, an empty modifier body is a solc compile error and never reaches the linter, and nested empty blocks are out of scope. BooleanCst.sol had an intentionally empty test helper the new lint flags; give it a trivial body to keep that fixture single-lint. Part of foundry-rs#14381.
0xMars42
requested review from
0xrusowsky,
DaniPopes,
figtracer,
grandizzy,
mablr,
mattsse and
stevencartavia
as code owners
The empty-block lint runs during forge build and added a warning to the can_fail_compile_with_warnings snapshots. Emit an event so the fixture stays lint-silent; the test is about compiler warnings (SPDX), not the function body.
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mablr
reviewed
Jul 2, 2026
mablr
reviewed
Jul 2, 2026
The empty-block lint fires on the empty mixed-case fixture functions and broke the exact stderr snapshots of the lint config tests. Give each one a statement that neither solc nor any lint flags: a state write in ContractWithLints (compiled by the build tests, so the body must not add solc warnings) and a local declaration in the lint-only fixtures.
…odies
Two review findings:
- functions with modifiers commonly wrap an intentionally empty body
(initialize() external initializer {}, _authorizeUpgrade(address)
internal override onlyOwner {}): the modifier carries the behavior,
so they are exempt now;
- the blanket payable exemption also suppressed empty payable functions
with return values, which silently return the default and read as an
unfinished stub: payable is exempt only without return values.
stevencartavia
approved these changes
Jul 3, 2026
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Motivation
empty-blockis one of the unchecked items of #14381: an empty body on a regular function is dead or unfinished code. This mirrors Aderyn'sempty-blockdetector (aderyn_core/src/detect/low/empty_block.rs), restricted to function bodies.Solution
New
Lowseverity early pass: fires on a regular function whose body is{}(a comment does not make a body non-empty).Exempt, because the empty body is the behavior:
receive/fallback(same as Aderyn): base calls, deployability, accepting ether or unknown calls;virtualfunctions: an empty body is the intentional default of an extension hook meant to be overridden (deviation from Aderyn, which has no such exemption);payablefunctions: an intentional ether sink, e.g.function deposit() external payable {}(deviation from Aderyn).Functions without a body (interfaces, abstract declarations) never fire, and an empty modifier body is a solc compile error (2883), so it never reaches the linter. Empty blocks nested inside a non-empty body (
if (x) {}) are out of scope: the checklist item is "Empty function body", while Aderyn also flags any nested empty block.BooleanCst.solhad an intentionally empty test helper (takesBool) that the new lint flags; it now has a trivial body so the fixture stays single-lint.Test
testdata/EmptyBlock.solcovers the firing forms (free function, library function, each visibility and mutability, comment-only body, empty non-virtual override, empty body behind a modifier) and the exempt forms (constructor with a parameter, constructor with a base call, receive/fallback, virtual hook, virtual override middle hook, payable sink, bodiless declaration, nested emptyif).Running the detector over the repo's own
testdata/Solidity fixtures yields 16 findings, all empty test helpers in.t.solfiles (e.g.doNotRevert()incheats/ExpectRevert.t.sol), none in non-test sources.Part of #14381.