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JS: recognize more conditionals in useless-conditional #404

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semmle-qlci merged 2 commits into from
Nov 7, 2018
Merged

JS: recognize more conditionals in useless-conditional #404

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56707fc
JS: recognize more conditionals in useless-conditional
asger-semmle Oct 31, 2018
87e0027
JS: address comments
asger-semmle Nov 5, 2018
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8 changes: 5 additions & 3 deletions javascript/ql/src/Statements/UselessConditional.ql
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Original file line number Diff line number Diff line change
Expand Up @@ -120,9 +120,11 @@ predicate whitelist(Expr e) {
*/
predicate isConditional(ASTNode cond, Expr e) {
e = cond.(IfStmt).getCondition() or
e = cond.(LoopStmt).getTest() or
e = cond.(ConditionalExpr).getCondition() or
e = cond.(LogAndExpr).getLeftOperand() or
e = cond.(LogOrExpr).getLeftOperand()
e = cond.(LogicalBinaryExpr).getLeftOperand() or
// Include `z` in `if (x && z)`.
isConditional(_, cond) and e = cond.(Expr).getUnderlyingValue().(LogicalBinaryExpr).getRightOperand()
}

from ASTNode cond, DataFlow::AnalyzedNode op, boolean cv, ASTNode sel, string msg
Expand All @@ -132,7 +134,7 @@ where isConditional(cond, op.asExpr()) and

// if `cond` is of the form `<non-trivial truthy expr> && <something>`,
// we suggest replacing it with `<non-trivial truthy expr>, <something>`
if cond instanceof LogAndExpr and cv = true and not op.asExpr().isPure() then
if cond.(LogAndExpr).getLeftOperand() = op.asExpr() and cv = true and not op.asExpr().isPure() then
(sel = cond and msg = "This logical 'and' expression can be replaced with a comma expression.")

// otherwise we just report that `op` always evaluates to `cv`
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5 changes: 5 additions & 0 deletions javascript/ql/test/query-tests/Statements/UselessConditional/UselessConditional.expected
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Expand Up @@ -16,6 +16,11 @@
| UselessConditional.js:76:13:76:13 | x | This use of variable 'x' always evaluates to true. |
| UselessConditional.js:82:13:82:13 | x | This use of variable 'x' always evaluates to true. |
| UselessConditional.js:89:10:89:16 | x, true | This expression always evaluates to true. |
| UselessConditional.js:94:16:94:16 | x | This use of variable 'x' always evaluates to false. |
| UselessConditional.js:100:13:100:24 | true && true | This expression always evaluates to true. |
| UselessConditional.js:101:18:101:18 | x | This use of variable 'x' always evaluates to false. |
| UselessConditional.js:102:19:102:19 | x | This use of variable 'x' always evaluates to false. |
| UselessConditional.js:103:23:103:23 | x | This use of variable 'x' always evaluates to false. |
| UselessConditionalGood.js:58:12:58:13 | x2 | This use of variable 'x2' always evaluates to false. |
| UselessConditionalGood.js:69:12:69:13 | xy | This use of variable 'xy' always evaluates to false. |
| UselessConditionalGood.js:85:12:85:13 | xy | This use of variable 'xy' always evaluates to false. |
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15 changes: 15 additions & 0 deletions javascript/ql/test/query-tests/Statements/UselessConditional/UselessConditional.js
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Expand Up @@ -89,4 +89,19 @@ async function awaitFlow(){
if ((x, true));
});

(function (x, y) {
if (!x) {
while (x) { // NOT OK
f();
}
while (true) { // OK
break;
}
if (true && true) {} // NOT OK
if (y && x) {} // NOT OK
if (y && (x)) {} // NOT OK
do { } while (x); // NOT OK
}
});

// semmle-extractor-options: --experimental