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Nov 27, 2025
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Rust: Model async return types as dyn Future #20236

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16 changes: 11 additions & 5 deletions rust/ql/lib/codeql/rust/internal/TypeInference.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -629,7 +629,7 @@ private predicate typeEquality(AstNode n1, TypePath prefix1, AstNode n2, TypePat
n2 = be.getStmtList().getTailExpr() and
if be.isAsync()
then
prefix1 = TypePath::singleton(getFutureOutputTypeParameter()) and
prefix1 = TypePath::singleton(getDynFutureOutputTypeParameter()) and
prefix2.isEmpty()
else (
prefix1.isEmpty() and
Expand Down Expand Up @@ -2053,7 +2053,7 @@ private module MethodCallMatchingInput implements MatchingWithEnvironmentInputSi
or
exists(TypePath suffix |
result = this.resolveRetType(suffix) and
path = TypePath::cons(getFutureOutputTypeParameter(), suffix)
path = TypePath::cons(getDynFutureOutputTypeParameter(), suffix)
)
else result = this.resolveRetType(path)
}
Expand Down Expand Up @@ -3024,13 +3024,18 @@ private Type inferLiteralType(LiteralExpr le, TypePath path, boolean certain) {
}

pragma[nomagic]
private TraitType getFutureTraitType() { result.getTrait() instanceof FutureTrait }
private DynTraitType getFutureTraitType() { result.getTrait() instanceof FutureTrait }

pragma[nomagic]
private AssociatedTypeTypeParameter getFutureOutputTypeParameter() {
result.getTypeAlias() = any(FutureTrait ft).getOutputType()
}

pragma[nomagic]
private DynTraitTypeParameter getDynFutureOutputTypeParameter() {
result = TDynTraitTypeParameter(any(FutureTrait ft).getOutputType())
}

pragma[nomagic]
predicate isUnitBlockExpr(BlockExpr be) {
not be.getStmtList().hasTailExpr() and
Expand All @@ -3047,7 +3052,7 @@ private Type inferBlockExprType(BlockExpr be, TypePath path) {
result = getFutureTraitType()
or
isUnitBlockExpr(be) and
path = TypePath::singleton(getFutureOutputTypeParameter()) and
path = TypePath::singleton(getDynFutureOutputTypeParameter()) and
result instanceof UnitType
) else (
isUnitBlockExpr(be) and
Expand All @@ -3072,6 +3077,7 @@ final private class AwaitTarget extends Expr {
}

private module AwaitSatisfiesConstraintInput implements SatisfiesConstraintInputSig<AwaitTarget> {
pragma[nomagic]
predicate relevantConstraint(AwaitTarget term, Type constraint) {
exists(term) and
constraint.(TraitType).getTrait() instanceof FutureTrait
Expand Down Expand Up @@ -3390,7 +3396,7 @@ private Type inferClosureExprType(AstNode n, TypePath path) {
exists(ClosureExpr ce |
n = ce and
path.isEmpty() and
result = TDynTraitType(any(FnOnceTrait t))
result = TDynTraitType(any(FnOnceTrait t)) // always exists because of the mention in `builtins/mentions.rs`
or
n = ce and
path = TypePath::singleton(TDynTraitTypeParameter(any(FnOnceTrait t).getTypeParam())) and
Expand Down
28 changes: 14 additions & 14 deletions rust/ql/test/library-tests/type-inference/type-inference.expected
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Expand Up @@ -4908,12 +4908,12 @@ inferType
| main.rs:2227:25:2229:5 | { ... } | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2228:9:2228:10 | S1 | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2231:41:2233:5 | { ... } | | main.rs:2231:16:2231:39 | impl ... |
| main.rs:2232:9:2232:20 | { ... } | | {EXTERNAL LOCATION} | trait Future |
| main.rs:2232:9:2232:20 | { ... } | Output | main.rs:2221:5:2221:14 | S1 |
| main.rs:2232:9:2232:20 | { ... } | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:2232:9:2232:20 | { ... } | dyn(Output) | main.rs:2221:5:2221:14 | S1 |
| main.rs:2232:17:2232:18 | S1 | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2235:41:2237:5 | { ... } | | main.rs:2235:16:2235:39 | impl ... |
| main.rs:2236:9:2236:16 | { ... } | | {EXTERNAL LOCATION} | trait Future |
| main.rs:2236:9:2236:16 | { ... } | Output | {EXTERNAL LOCATION} | () |
| main.rs:2236:9:2236:16 | { ... } | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:2236:9:2236:16 | { ... } | dyn(Output) | {EXTERNAL LOCATION} | () |
| main.rs:2245:13:2245:42 | SelfParam | | {EXTERNAL LOCATION} | Pin |
| main.rs:2245:13:2245:42 | SelfParam | Ptr | {EXTERNAL LOCATION} | & |
| main.rs:2245:13:2245:42 | SelfParam | Ptr.TRef | main.rs:2239:5:2239:14 | S2 |
Expand All @@ -4928,8 +4928,8 @@ inferType
| main.rs:2253:9:2253:10 | S2 | | main.rs:2239:5:2239:14 | S2 |
| main.rs:2253:9:2253:10 | S2 | | main.rs:2252:16:2252:39 | impl ... |
| main.rs:2256:22:2264:5 | { ... } | | {EXTERNAL LOCATION} | () |
| main.rs:2257:9:2257:12 | f1(...) | | {EXTERNAL LOCATION} | trait Future |
| main.rs:2257:9:2257:12 | f1(...) | Output | main.rs:2221:5:2221:14 | S1 |
| main.rs:2257:9:2257:12 | f1(...) | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:2257:9:2257:12 | f1(...) | dyn(Output) | main.rs:2221:5:2221:14 | S1 |
| main.rs:2257:9:2257:18 | await ... | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2257:9:2257:22 | ... .f() | | {EXTERNAL LOCATION} | () |
| main.rs:2258:9:2258:12 | f2(...) | | main.rs:2231:16:2231:39 | impl ... |
Expand All @@ -4943,13 +4943,13 @@ inferType
| main.rs:2261:9:2261:10 | S2 | | main.rs:2239:5:2239:14 | S2 |
| main.rs:2261:9:2261:16 | await S2 | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2261:9:2261:20 | ... .f() | | {EXTERNAL LOCATION} | () |
| main.rs:2262:13:2262:13 | b | | {EXTERNAL LOCATION} | trait Future |
| main.rs:2262:13:2262:13 | b | Output | main.rs:2221:5:2221:14 | S1 |
| main.rs:2262:17:2262:28 | { ... } | | {EXTERNAL LOCATION} | trait Future |
| main.rs:2262:17:2262:28 | { ... } | Output | main.rs:2221:5:2221:14 | S1 |
| main.rs:2262:13:2262:13 | b | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:2262:13:2262:13 | b | dyn(Output) | main.rs:2221:5:2221:14 | S1 |
| main.rs:2262:17:2262:28 | { ... } | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:2262:17:2262:28 | { ... } | dyn(Output) | main.rs:2221:5:2221:14 | S1 |
| main.rs:2262:25:2262:26 | S1 | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2263:9:2263:9 | b | | {EXTERNAL LOCATION} | trait Future |
| main.rs:2263:9:2263:9 | b | Output | main.rs:2221:5:2221:14 | S1 |
| main.rs:2263:9:2263:9 | b | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:2263:9:2263:9 | b | dyn(Output) | main.rs:2221:5:2221:14 | S1 |
| main.rs:2263:9:2263:15 | await b | | main.rs:2221:5:2221:14 | S1 |
| main.rs:2263:9:2263:19 | ... .f() | | {EXTERNAL LOCATION} | () |
| main.rs:2274:15:2274:19 | SelfParam | | {EXTERNAL LOCATION} | & |
Expand Down Expand Up @@ -6550,8 +6550,8 @@ inferType
| main.rs:3061:5:3061:24 | ...::f(...) | | {EXTERNAL LOCATION} | () |
| main.rs:3062:5:3062:17 | ...::f(...) | | {EXTERNAL LOCATION} | () |
| main.rs:3063:5:3063:18 | ...::f(...) | | {EXTERNAL LOCATION} | () |
| main.rs:3064:5:3064:15 | ...::f(...) | | {EXTERNAL LOCATION} | trait Future |
| main.rs:3064:5:3064:15 | ...::f(...) | Output | {EXTERNAL LOCATION} | () |
| main.rs:3064:5:3064:15 | ...::f(...) | | {EXTERNAL LOCATION} | dyn Future |
| main.rs:3064:5:3064:15 | ...::f(...) | dyn(Output) | {EXTERNAL LOCATION} | () |
| main.rs:3065:5:3065:19 | ...::f(...) | | {EXTERNAL LOCATION} | () |
| main.rs:3066:5:3066:17 | ...::f(...) | | {EXTERNAL LOCATION} | () |
| main.rs:3067:5:3067:14 | ...::f(...) | | {EXTERNAL LOCATION} | () |
Expand Down
6 changes: 6 additions & 0 deletions rust/tools/builtins/mentions.rs
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@@ -0,0 +1,6 @@
// Type mentions required by type inference

use std::future::Future;
fn mention_dyn_future<T>(f: &dyn Future<Output = T>) {}

Check notice

Code scanning / CodeQL

Unused variable Note

Variable 'f' is not used.

fn mention_dyn_fn_once<F>(f: &dyn FnOnce() -> F) {}

Check notice

Code scanning / CodeQL

Unused variable Note

Variable 'f' is not used.