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Rust: Improve handling of where clauses in type inference and path resolution #20140

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Rust: Improve handling of where clauses in type inference and path resolution #20140

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ce60fb9
Rust: Add tests with `where` clause
paldepind Jul 30, 2025
2313011
Rust: Improve handling of where clauses in type inference and path re…
paldepind Jul 30, 2025
c6fb8c1
Rust: Add example with multiple where clause items for the same type …
paldepind Aug 4, 2025
69ca7ff
Rust: Handle multiple type bounds for the same type parameter in `get…
paldepind Aug 4, 2025
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31 changes: 31 additions & 0 deletions rust/ql/lib/codeql/rust/elements/internal/TraitImpl.qll
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Expand Up @@ -36,5 +36,36 @@ module Impl {
not this.hasGenericParamList() and
result = 0
}

private int nrOfDirectTypeBounds() {
result = this.getTypeBoundList().getNumberOfBounds()
or
not this.hasTypeBoundList() and
result = 0
}

/**
* Gets the `index`th type bound of this trait, if any.
*
* This includes type bounds directly on the trait and bounds from any
* `where` clauses for `Self`.
*/
TypeBound getTypeBound(int index) {
result = this.getTypeBoundList().getBound(index)
or
exists(WherePred wp |
wp = this.getWhereClause().getAPredicate() and
wp.getTypeRepr().(PathTypeRepr).getPath().getText() = "Self" and
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[nitpick] The hardcoded string comparison getText() = \"Self\" is fragile and may not handle all valid representations of Self. Consider using a more robust method to identify Self type references, such as checking the resolved type or using semantic analysis rather than text comparison.

Suggested change
wp.getTypeRepr().(PathTypeRepr).getPath().getText() = "Self" and
wp.getTypeRepr() instanceof SelfTypeRepr and

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result = wp.getTypeBoundList().getBound(index - this.nrOfDirectTypeBounds())
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It appears to be legal to have two where predicates with Self as the path, e.g.:

    trait Subtrait
    where
        Self: Supertrait1,
        Self: Supertrait2,

I think at the moment this will break your index numbering.

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You're right, that is legal and the implementation currently does not account for that.

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Did this one get fixed? If not can you write it up as an issue and lets get this PR merged!

)
}

/**
* Gets a type bound of this trait.
*
* This includes type bounds directly on the trait and bounds from any
* `where` clauses for `Self`.
*/
TypeBound getATypeBound() { result = this.getTypeBound(_) }
}
}
36 changes: 36 additions & 0 deletions rust/ql/lib/codeql/rust/elements/internal/TypeParamImpl.qll
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Expand Up @@ -12,6 +12,7 @@ private import codeql.rust.elements.internal.generated.TypeParam
*/
module Impl {
private import rust
private import codeql.rust.internal.PathResolution

// the following QLdoc is generated: if you need to edit it, do it in the schema file
/**
Expand All @@ -27,6 +28,41 @@ module Impl {
/** Gets the position of this type parameter. */
int getPosition() { this = any(GenericParamList l).getTypeParam(result) }

private TypeBound getTypeBoundAt(int i, int j) {
exists(TypeBoundList tbl | result = tbl.getBound(j) |
tbl = this.getTypeBoundList() and i = 0
or
exists(WherePred wp |
wp = this.(TypeParamItemNode).getAWherePred() and
tbl = wp.getTypeBoundList() and
wp = any(WhereClause wc).getPredicate(i)
)
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I feel like this case should simplify to tbl = this.(TypeParamItemNode).getWherePred(i).getTypeBoundList() (except that getWherePred(i) doesn't exist there). I don't feel strongly if this is a pain to change.

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I'll give it a try. I had that predicate before, but ran into non-monotonic recursion. But it should be doable as long as the getWherePred(i) is not actually used in path resolution itself.

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I agree that what you propose is a lot cleaner, but the getWherePred on TypeParamItemNode would have to use rank and then we got non-monotonic recursion 😢

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No problem, don't spend any more time on it!

)
}
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[nitpick] The getTypeBoundAt method uses magic numbers and has unclear indexing logic. Consider adding documentation to explain the indexing scheme where i=0 represents direct bounds and i>0 represents where clause predicates, or use more descriptive parameter names like source and boundIndex.

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/**
* Gets the `index`th type bound of this type parameter, if any.
*
* This includes type bounds directly on this type parameter and bounds from
* any `where` clauses for this type parameter.
*/
TypeBound getTypeBound(int index) {
result = rank[index + 1](int i, int j | | this.getTypeBoundAt(i, j) order by i, j)
}

/**
* Gets a type bound of this type parameter.
*
* This includes type bounds directly on this type parameter and bounds from
* any `where` clauses for this type parameter.
*/
TypeBound getATypeBound() {
// NOTE: This predicate is used in path resolution, so it can not be
// defined using `getTypeBound` as that would cause non-monotonic
// recursion due to the `rank`.
result = this.getTypeBoundAt(_, _)
}

override string toAbbreviatedString() { result = this.getName().getText() }

override string toStringImpl() { result = this.getName().getText() }
Expand Down
22 changes: 5 additions & 17 deletions rust/ql/lib/codeql/rust/internal/PathResolution.qll
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Expand Up @@ -791,9 +791,7 @@ private class StructItemNode extends TypeItemNode instanceof Struct {

class TraitItemNode extends ImplOrTraitItemNode, TypeItemNode instanceof Trait {
pragma[nomagic]
Path getABoundPath() {
result = super.getTypeBoundList().getABound().getTypeRepr().(PathTypeRepr).getPath()
}
Path getABoundPath() { result = super.getATypeBound().getTypeRepr().(PathTypeRepr).getPath() }

pragma[nomagic]
ItemNode resolveABound() { result = resolvePath(this.getABoundPath()) }
Expand Down Expand Up @@ -924,7 +922,8 @@ private class BlockExprItemNode extends ItemNode instanceof BlockExpr {
}

class TypeParamItemNode extends TypeItemNode instanceof TypeParam {
private WherePred getAWherePred() {
/** Gets a where predicate for this type parameter, if any */
WherePred getAWherePred() {
exists(ItemNode declaringItem |
this = resolveTypeParamPathTypeRepr(result.getTypeRepr()) and
result = declaringItem.getADescendant() and
Expand All @@ -933,13 +932,7 @@ class TypeParamItemNode extends TypeItemNode instanceof TypeParam {
}

pragma[nomagic]
Path getABoundPath() {
exists(TypeBoundList tbl | result = tbl.getABound().getTypeRepr().(PathTypeRepr).getPath() |
tbl = super.getTypeBoundList()
or
tbl = this.getAWherePred().getTypeBoundList()
)
}
Path getABoundPath() { result = super.getATypeBound().getTypeRepr().(PathTypeRepr).getPath() }

pragma[nomagic]
ItemNode resolveABound() { result = resolvePath(this.getABoundPath()) }
Expand All @@ -956,12 +949,7 @@ class TypeParamItemNode extends TypeItemNode instanceof TypeParam {
* ```
*/
cached
predicate hasTraitBound() {
Stages::PathResolutionStage::ref() and
exists(this.getABoundPath())
or
exists(this.getAWherePred())
}
predicate hasTraitBound() { Stages::PathResolutionStage::ref() and exists(this.getABoundPath()) }

/**
* Holds if this type parameter has no trait bound. Examples:
Expand Down
6 changes: 3 additions & 3 deletions rust/ql/lib/codeql/rust/internal/TypeInference.qll
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Expand Up @@ -151,7 +151,7 @@ private module Input2 implements InputSig2 {
TypeMention getABaseTypeMention(Type t) { none() }

TypeMention getATypeParameterConstraint(TypeParameter tp) {
result = tp.(TypeParamTypeParameter).getTypeParam().getTypeBoundList().getABound().getTypeRepr()
result = tp.(TypeParamTypeParameter).getTypeParam().getATypeBound().getTypeRepr()
or
result = tp.(SelfTypeParameter).getTrait()
or
Expand Down Expand Up @@ -184,12 +184,12 @@ private module Input2 implements InputSig2 {
exists(Trait trait |
abs = trait and
condition = trait and
constraint = trait.getTypeBoundList().getABound().getTypeRepr()
constraint = trait.getATypeBound().getTypeRepr()
)
or
// trait bounds on type parameters
exists(TypeParam param |
abs = param.getTypeBoundList().getABound() and
abs = param.getATypeBound() and
condition = param and
constraint = abs.(TypeBound).getTypeRepr()
)
Expand Down
6 changes: 3 additions & 3 deletions rust/ql/test/library-tests/path-resolution/CONSISTENCY/PathResolutionConsistency.expected
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Expand Up @@ -2,6 +2,6 @@ multipleCallTargets
| main.rs:118:9:118:11 | f(...) |
| proc_macro.rs:9:5:11:5 | ...::new(...) |
multiplePathResolutions
| main.rs:626:3:626:12 | proc_macro |
| main.rs:632:7:632:16 | proc_macro |
| main.rs:635:7:635:16 | proc_macro |
| main.rs:641:3:641:12 | proc_macro |
| main.rs:647:7:647:16 | proc_macro |
| main.rs:650:7:650:16 | proc_macro |
15 changes: 15 additions & 0 deletions rust/ql/test/library-tests/path-resolution/main.rs
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Expand Up @@ -312,6 +312,21 @@ mod m15 {
}
} // I82

#[rustfmt::skip]
trait Trait3<
TT // ITT
>
where
Self: Trait1, // $ item=ITrait3 item=I79
TT: Trait1, // $ item=ITT item=I79
{
fn f(&self, tt: TT) { // $ item=ITT
Self::g(self); // $ item=I80
TT::g(&tt); // $ item=I80
self.g(); // $ item=I80
}
} // ITrait3

struct S; // I81

#[rustfmt::skip]
Expand Down
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