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fix >>> (unsigned right shift) producing wrong results on Lua 5.3+ #1703

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fix >>> (unsigned right shift) producing wrong results on Lua 5.3+ #1703

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6de84d3
fix >>> (unsigned right shift) producing wrong results on Lua 5.3+
RealColdFry Apr 1, 2026
83ba540
lint
RealColdFry Apr 1, 2026
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16 changes: 16 additions & 0 deletions src/transformation/visitors/binary-expression/bit.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,22 @@ export function transformBinaryBitOperation(
case LuaTarget.Lua52:
return transformBinaryBitLibOperation(node, left, right, operator, "bit32");
default:
// Lua 5.3+ `>>` is arithmetic (sign-extending), but TS `>>>` is logical (zero-fill).
// Emit `(left & 0xFFFFFFFF) >> right` to convert to unsigned 32-bit first.
if (operator === ts.SyntaxKind.GreaterThanGreaterThanGreaterThanToken) {
const mask = lua.createBinaryExpression(
left,
lua.createNumericLiteral(0xffffffff, node),
lua.SyntaxKind.BitwiseAndOperator,
node
);
return lua.createBinaryExpression(
lua.createParenthesizedExpression(mask, node),
right,
lua.SyntaxKind.BitwiseRightShiftOperator,
node
);
}
const luaOperator = transformBitOperatorToLuaOperator(context, node, operator);
return lua.createBinaryExpression(left, right, luaOperator, node);
}
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12 changes: 6 additions & 6 deletions test/unit/__snapshots__/expressions.spec.ts.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -374,14 +374,14 @@ return ____exports"

exports[`Bitop [5.3] ("a>>>=b") 1`] = `
"local ____exports = {}
a = a >> b
a = (a & 4294967295) >> b
____exports.__result = a
return ____exports"
`;

exports[`Bitop [5.3] ("a>>>b") 1`] = `
"local ____exports = {}
____exports.__result = a >> b
____exports.__result = (a & 4294967295) >> b
return ____exports"
`;

Expand Down Expand Up @@ -445,14 +445,14 @@ return ____exports"

exports[`Bitop [5.4] ("a>>>=b") 1`] = `
"local ____exports = {}
a = a >> b
a = (a & 4294967295) >> b
____exports.__result = a
return ____exports"
`;

exports[`Bitop [5.4] ("a>>>b") 1`] = `
"local ____exports = {}
____exports.__result = a >> b
____exports.__result = (a & 4294967295) >> b
return ____exports"
`;

Expand Down Expand Up @@ -516,14 +516,14 @@ return ____exports"

exports[`Bitop [5.5] ("a>>>=b") 1`] = `
"local ____exports = {}
a = a >> b
a = (a & 4294967295) >> b
____exports.__result = a
return ____exports"
`;

exports[`Bitop [5.5] ("a>>>b") 1`] = `
"local ____exports = {}
____exports.__result = a >> b
____exports.__result = (a & 4294967295) >> b
return ____exports"
`;

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29 changes: 29 additions & 0 deletions test/unit/expressions.spec.ts
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Expand Up @@ -117,6 +117,35 @@ test.each(unsupportedIn53And54)("Unsupported bitop 5.4 (%p)", input => {
.expectDiagnosticsToMatchSnapshot([unsupportedRightShiftOperator.code]);
});

// Execution tests: verify >>> produces correct results matching JS semantics
for (const expression of ["-5 >>> 0", "-1 >>> 0", "1 >>> 0", "-1 >>> 16", "255 >>> 4"]) {
util.testEachVersion(`Unsigned right shift execution (${expression})`, () => util.testExpression(expression), {
[tstl.LuaTarget.Universal]: false,
[tstl.LuaTarget.Lua50]: false, // No bit library in WASM runtime
[tstl.LuaTarget.Lua51]: false, // No bit library in WASM runtime
[tstl.LuaTarget.Lua52]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.Lua53]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.Lua54]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.Lua55]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.LuaJIT]: false, // Can't execute LuaJIT in tests
[tstl.LuaTarget.Luau]: false,
});
}

for (const code of ["let a = -5; a >>>= 0; return a;", "let a = -1; a >>>= 16; return a;"]) {
util.testEachVersion(`Unsigned right shift assignment execution (${code})`, () => util.testFunction(code), {
[tstl.LuaTarget.Universal]: false,
[tstl.LuaTarget.Lua50]: false, // No bit library in WASM runtime
[tstl.LuaTarget.Lua51]: false, // No bit library in WASM runtime
[tstl.LuaTarget.Lua52]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.Lua53]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.Lua54]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.Lua55]: builder => builder.expectToMatchJsResult(),
[tstl.LuaTarget.LuaJIT]: false, // Can't execute LuaJIT in tests
[tstl.LuaTarget.Luau]: false,
});
}

test.each(["1+1", "-1+1", "1*30+4", "1*(3+4)", "1*(3+4*2)", "10-(4+5)"])(
"Binary expressions ordering parentheses (%p)",
input => {
Expand Down
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