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JS: Add query for missing await
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‎javascript/ql/src/Expressions/MissingAwait.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>
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In JavaScript, <code>async</code> functions always return a Promise object.
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</p>
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<p>
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PLACEHOLDER
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</p>
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</overview>
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<recommendation>
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<p>
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PLACEHOLDER
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</p>
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</recommendation>
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<example>
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<p>
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PLACEHOLDER
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</p>
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<sample src="examples/ImplicitOperandConversion.js" />
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<p>
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PLACEHOLDER
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</p>
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<p>
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PLACEHOLDER
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</p>
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<sample src="examples/ImplicitOperandConversionGood.js" />
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<p>
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PLACEHOLDER
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</p>
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<sample src="examples/ImplicitOperandConversion2.js" />
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<p>
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PLACEHOLDER
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</p>
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<sample src="examples/ImplicitOperandConversion2Good.js" />
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<p>
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PLACEHOLDER
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</p>
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<sample src="examples/ImplicitOperandConversion2Good2.js" />
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</example>
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<references>
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<li>Ecma International, <i>ECMAScript Language Definition</i>, 5.1 Edition, Section 9. ECMA, 2011.</li>
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</references>
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</qhelp>

‎javascript/ql/src/Expressions/MissingAwait.ql‎

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/**
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* @name Missing await
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* @description Using a promise without awaiting its result can cause unexpected behavior.
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* @kind problem
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* @problem.severity warning
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* @id js/missing-await
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* @tags correctness
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* @precision high
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*/
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import javascript
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predicate isAsyncCall(DataFlow::CallNode call) {
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forex(Function callee | call.getACallee() = callee | callee.isAsync())
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}
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/**
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* Holds if `node` is always a promise.
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*/
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predicate isPromise(DataFlow::SourceNode node, boolean nullable) {
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isAsyncCall(node) and
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nullable = false
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or
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not isAsyncCall(node) and
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node.asExpr().getType() instanceof PromiseType and
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nullable = true
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}
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/**
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* Holds the result of `e` is used in a way that doesn't make sense for Promise objects.
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*/
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predicate isBadPromiseContext(Expr expr) {
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exists(BinaryExpr binary |
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expr = binary.getAnOperand() and
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not binary instanceof LogicalExpr and
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not binary instanceof InstanceofExpr
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)
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or
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expr = any(LogicalBinaryExpr e).getLeftOperand()
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or
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expr = any(UnaryExpr e).getOperand()
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or
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expr = any(UpdateExpr e).getOperand()
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}
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string tryGetPromiseExplanation(Expr e) {
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result = "The value '" + e.(VarAccess).getName() + "' is always a promise."
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or
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result = "The call to '" + e.(CallExpr).getCalleeName() + "' always returns a promise."
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}
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string getPromiseExplanation(Expr e) {
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result = tryGetPromiseExplanation(e)
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or
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not exists(tryGetPromiseExplanation(e)) and
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result = "This value is always a promise."
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}
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from Expr expr, boolean nullable
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where
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isBadPromiseContext(expr) and
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isPromise(expr.flow().getImmediatePredecessor*(), nullable) and
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(
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nullable = false
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or
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expr.inNullSensitiveContext()
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)
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select expr, "Missing await. " + getPromiseExplanation(expr)

‎javascript/ql/test/query-tests/Expressions/MissingAwait/MissingAwait.expected‎

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| tst.js:8:9:8:13 | thing | Missing await. The value 'thing' is always a promise. |
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| tst.js:32:12:32:16 | thing | Missing await. The value 'thing' is always a promise. |

‎javascript/ql/test/query-tests/Expressions/MissingAwait/MissingAwait.qlref‎

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Expressions/MissingAwait.ql

‎javascript/ql/test/query-tests/Expressions/MissingAwait/tst.js‎

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async function getThing() {
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return something();
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}
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function useThing() {
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let thing = getThing();
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if (thing === undefined) {} // NOT OK
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if (thing == null) {} // NOT OK
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return thing + "bar"; // NOT OK
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}
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async function useThingCorrectly() {
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let thing = await getThing();
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if (thing === undefined) {} // OK
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if (thing == null) {} // OK
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return thing + "bar"; // OK
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}
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async function useThingCorrectly2() {
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let thing = getThing();
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if (await thing === undefined) {} // OK
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if (await thing == null) {} // OK
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return thing + "bar"; // NOT OK
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}
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function getThingSync() {
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return something();
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}
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function useThingPossiblySync(b) {
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let thing = b ? getThing() : getThingSync();
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if (thing === undefined) {} // OK
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if (thing == null) {} // OK
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return thing + "bar"; // NOT OK - but we don't flag it
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}

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