Disallow passing a empty array type to `abi` functions. #16416

rodiazet · 2026-01-23T15:42:23Z

This PR adds additional check in TypeChecker for IndexAccess which ensures that the array size is not 0.
As a result of this change, type which is an empty array of contracts is also forbidden.

Fixes #13652.

stackenbotten3000 · 2026-01-23T15:43:12Z

There was an error when running chk_coding_style for commit aa31d42a9b1c270b3d5024b70e97d60c34f33da8:

Coding style error:
libsolidity/analysis/TypeChecker.cpp:26:#include "DeclarationTypeChecker.h"

Please check that your changes are working as intended.

stackenbotten3000 · 2026-01-23T15:43:12Z

libsolidity/analysis/TypeChecker.cpp


 #include <libsolidity/analysis/TypeChecker.h>
+
+#include "DeclarationTypeChecker.h"


Coding style error

stackenbotten3000 · 2026-01-23T15:47:53Z

There was an error when running chk_coding_style for commit 12c94081a054bcce42ac0aa36bf24a9360ee4bcc:

Coding style error:
libsolidity/analysis/TypeChecker.cpp:26:#include "DeclarationTypeChecker.h"

Please check that your changes are working as intended.

stackenbotten3000 · 2026-01-23T15:47:54Z

libsolidity/analysis/TypeChecker.cpp


 #include <libsolidity/analysis/TypeChecker.h>
+
+#include "DeclarationTypeChecker.h"


Coding style error

nikola-matic

Changelog

cameel · 2026-01-26T19:27:45Z

test/libsolidity/syntaxTests/array/invalid/library_index_access.sol

 library C {
    function f() view public {
-        C[0];
+        C[1];


Can you also add new cases testing specifically for the case of zero length in a situation like this? Or do we have them already?

Also, I'd add variants for interfaces for completeness.

And rename C here to L (we usually use C for a contract so it makes it easy to confuse things).

cameel · 2026-01-26T19:31:29Z

test/libsolidity/syntaxTests/array/zero_length_array_type.sol

This test is specifically about decoding so I'd rename it to abi_decode_zero_length_array_type.sol. You can have int[0] in other situations and this test is not checking them.

BTW, I'm assuming we already have coverage for those other cases, but maybe check whether that's the case. These are ones I can think of:

Variable declaration

Contract variable (uint[0] x;, mapping(uint => uint[0]) m;, function() returns (uint[0] memory) f;)

Local variable (uint[0] storage x;)

Function arguments and returns

Try/catch statement (try this.g() returns (uint[0] memory) {} catch (bytes memory b) {})

Tuple declaration ((uint[0] memory a, uint b) = ([], 1);)

Struct field (struct S { uint[0] x; })

Error and event parameters

Array allocation (new uint[0][](3); })

No-op statement consisting of just the type (uint[0];)

Technically, these but are disallowed for various other reasons in analysis, but are still valid syntax, so would not hurt to have them covered:

UDVT declaration (type U is uint[0];)

type() builtin (type(uint[0])).

Ternary operator (true ? uint[0] : uint[0])

Inline Array indexing ([uint[0]][0])

Oh, I see f6() is actually not decoding. I'd still split it into separate tests though.

Reworked and more tests added.

cameel · 2026-01-26T19:50:02Z

test/libsolidity/syntaxTests/array/zero_length_array_type.sol

@@ -0,0 +1,38 @@
+contract C {
+    function f0() public {
+        abi.decode("",  (int[0]));


Suggested change

abi.decode("", (int[0]));

abi.decode("", (int[0]));

cameel · 2026-01-26T19:58:58Z

test/libsolidity/syntaxTests/array/zero_length_array_type.sol

Please also add the case from #13652 (comment). That one was not a compilation error so it's important that this no longer allowed:

contract C { function f() public returns (bytes memory) { return abi.encode(abi.decode("", (int[0]))); } }

Added as a separated test case.

cameel · 2026-01-26T20:08:47Z

test/libsolidity/syntaxTests/array/zero_length_array_type.sol

Please also add a dedicated case for super (which is actually a type):

contract C { function f() public { super[0]; } }

contract C { function f() public { super[0] s; } }

Interestingly, an array of super is a valid expression on its own (super[3];) even though you cannot use it in a variable declaration (super[3] s;). I think it should be disallowed in either case.

I suspect that we have more things like this. Would be good to take a look at DeclarationTypeChecker and compare what other checks it has for ArrayTypeName that we do not here. Perhaps we should extract them into a shared function to avoid such discrepancies in the future.

Also, pinging @matheusaaguiar to pay attention to this in test cases related to comptime. Looks like we have two places in the code where we evaluate array sizes. These should always behave the same way.

Also, WTF, why does every random issue recently turn out to be related to comptime one way or another :D

Do not open your refrigerator.

I reworked this part and put common logic in separated function, where it was possible.

stackenbotten3000 · 2026-02-03T16:38:29Z

libsolidity/analysis/DeclarationTypeChecker.cpp

 #include <libsolidity/analysis/DeclarationTypeChecker.h>

-#include <libsolidity/analysis/ConstantEvaluator.h>
+#include "TypeChecker.h"


Coding style error

stackenbotten3000 · 2026-02-03T16:38:30Z

libsolidity/analysis/TypeChecker.cpp


 #include <libsolidity/analysis/TypeChecker.h>
+
+#include "ConstantEvaluator.h"


Coding style error

stackenbotten3000 · 2026-02-03T16:38:30Z

libsolidity/analysis/TypeChecker.cpp

 	{
 		TypeType const& typeType = dynamic_cast<TypeType const&>(*baseType);
-		if (auto const* contractType = dynamic_cast<ContractType const*>(typeType.actualType()))
+		const auto actualType = typeType.actualType();


Coding style error

stackenbotten3000 · 2026-02-03T16:38:31Z

libsolidity/analysis/TypeChecker.cpp

 		TypeType const& typeType = dynamic_cast<TypeType const&>(*baseType);
-		if (auto const* contractType = dynamic_cast<ContractType const*>(typeType.actualType()))
+		const auto actualType = typeType.actualType();
+		const auto actualTypeCategory = actualType->category();


Coding style error

nikola-matic · 2026-02-03T16:44:50Z

Run ./scripts/check_style.sh before pushing to avoid style errors.

stackenbotten3000 · 2026-02-04T08:46:37Z

libsolidity/analysis/TypeChecker.cpp

 	{
 		TypeType const& typeType = dynamic_cast<TypeType const&>(*baseType);
-		if (auto const* contractType = dynamic_cast<ContractType const*>(typeType.actualType()))
+		const auto actualType = typeType.actualType();


Coding style error

stackenbotten3000 · 2026-02-04T08:46:38Z

libsolidity/analysis/TypeChecker.cpp

 		TypeType const& typeType = dynamic_cast<TypeType const&>(*baseType);
-		if (auto const* contractType = dynamic_cast<ContractType const*>(typeType.actualType()))
+		const auto actualType = typeType.actualType();
+		const auto actualTypeCategory = actualType->category();


Coding style error

This error is not issued when running the script locally.

AI says so:

With git grep -E, the regex engine is POSIX extended regex. In that dialect, \s is not a whitespace escape (that’s a PCRE/Perl thing). So: ^\s* is effectively interpreted as ^s* (i.e., “zero or more s characters at BOL”) which means it won’t match indentation made of spaces/tabs

As usual, AI is full of shit. You're getting the error because you're using const auto ... instead of auto const .... What OS are you running locally?

I know what was the problem, but this script doesn't find the pattern. And this is good explanation. I'm using MacOS with git in the newest version 2.52.0.

AI proposed to change \sto [[:space:]], because (POSIX ERE) does not understand \s :)

Looks like it's right. https://en.wikibooks.org/wiki/Regular_Expressions/POSIX-Extended_Regular_Expressions

On the other hand it looks like they should be supported too https://www.boost.org/doc/libs/1_71_0/libs/regex/doc/html/boost_regex/syntax/basic_extended.html#boost_regex.syntax.basic_extended.single_character_character_class
~~Probable for some reason MacOS does not support it.~~
It's for boost.regexp only

Copilot

Pull request overview

This PR fixes issue #13652 by adding validation to prevent zero-length arrays from being used in expression contexts like abi.decode, which previously caused internal compiler errors during code generation. The fix adds a new shared validation function checkArrayLengthExpression that ensures array lengths are non-zero, positive integers within valid bounds.

Changes:

Added TypeChecker::checkArrayLengthExpression function to validate array length expressions
Refactored array length validation logic to use the new shared function in both TypeChecker (for expression contexts) and DeclarationTypeChecker (for declaration contexts)
Added comprehensive test coverage for zero-length arrays in various contexts (abi.decode, inline arrays, conditionals, type expressions, etc.)

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
libsolidity/analysis/TypeChecker.h	Added declaration for new static `checkArrayLengthExpression` function
libsolidity/analysis/TypeChecker.cpp	Implemented `checkArrayLengthExpression` function and refactored `IndexAccess` visitor to validate array lengths and handle super/library types more explicitly
libsolidity/analysis/DeclarationTypeChecker.cpp	Refactored to use the new shared `checkArrayLengthExpression` function instead of duplicate validation logic
test/libsolidity/syntaxTests/array/invalid/abi_decode_zero_length_array_type.sol	New test covering the exact issue case with various multi-dimensional array patterns
test/libsolidity/syntaxTests/array/invalid/abi_encode_decode_zero_length_array_type.sol	New test for abi.encode with zero-length arrays
test/libsolidity/syntaxTests/array/invalid/contract_zero_index_access.sol	New test for contract type with zero-length array
test/libsolidity/syntaxTests/array/invalid/interface_zero_index_access.sol	New test for interface type with zero-length array
test/libsolidity/syntaxTests/array/invalid/library_zero_index_access.sol	New test for library type with zero-length array (shows both errors)
test/libsolidity/syntaxTests/array/invalid/super_index_access.sol	New test for super keyword with index access
test/libsolidity/syntaxTests/array/length/*.sol	Multiple new tests for zero-length arrays in different contexts (inline arrays, type expressions, conditionals)
test/libsolidity/syntaxTests/array/length/fixed_size_zero_length.sol	Expanded test with more zero-length array scenarios
test/libsolidity/syntaxTests/array/type_type_index_expression.sol	New test showing valid index expressions with various types
test/libsolidity/syntaxTests/array/contract_index_access.sol	Updated test to use non-zero index and pure function
test/libsolidity/syntaxTests/array/interface_index_access.sol	New test for valid interface array type
test/libsolidity/syntaxTests/array/invalid/library_index_access.sol	Updated test for clarity (renamed library)
test/libsolidity/syntaxTests/nameAndTypeResolution/366_invalid_array_as_statement.sol	Updated expected error message
test/libsolidity/syntaxTests/indexing/struct_array_noninteger_index.sol	Updated expected error message

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libsolidity/analysis/TypeChecker.cpp

…clarationTypeChecker`

cameel · 2026-02-06T15:59:16Z

rodiazet closed this in #16441 39 minutes ago

Hmm... looks like Fixes <comment URL> does not work the way you think it does :P

rodiazet requested review from cameel and nikola-matic and removed request for nikola-matic January 23, 2026 15:42

stackenbotten3000 reviewed Jan 23, 2026

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rodiazet force-pushed the zere_length_array branch from aa31d42 to 12c9408 Compare January 23, 2026 15:47

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rodiazet force-pushed the zere_length_array branch from 12c9408 to bc948b5 Compare January 23, 2026 15:49

nikola-matic reviewed Jan 26, 2026

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cameel reviewed Jan 26, 2026

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rodiazet force-pushed the zere_length_array branch from bc948b5 to 0bc0d0b Compare February 3, 2026 16:33

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rodiazet force-pushed the zere_length_array branch from 0bc0d0b to e7e72c7 Compare February 4, 2026 08:40

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rodiazet force-pushed the zere_length_array branch from 7c5c3f2 to 56065c7 Compare February 4, 2026 09:02

rodiazet mentioned this pull request Feb 4, 2026

Fix check_style.sh. Replace \s to [[:space:]] #16441

Merged

rodiazet force-pushed the zere_length_array branch from 56065c7 to 8537278 Compare February 5, 2026 09:28

rodiazet requested a review from Copilot February 5, 2026 09:53

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libsolidity/analysis/TypeChecker.cpp Show resolved Hide resolved

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rodiazet added 2 commits February 5, 2026 11:11

Rework validation of array length expression in TypeChecker and `De…

0e9f797

…clarationTypeChecker`

Add and update tests.

a01870d

rodiazet force-pushed the zere_length_array branch from 8537278 to a01870d Compare February 5, 2026 10:13

rodiazet closed this in #16441 Feb 6, 2026

cameel reopened this Feb 6, 2026


		#include <libsolidity/analysis/TypeChecker.h>

		#include "DeclarationTypeChecker.h"


		#include <libsolidity/analysis/TypeChecker.h>

		#include "ConstantEvaluator.h"

Disallow passing a empty array type to abi functions. #16416

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Disallow passing a empty array type to abi functions. #16416

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Disallow passing a empty array type to `abi` functions. #16416

Disallow passing a empty array type to `abi` functions. #16416

cameel Jan 26, 2026 •

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