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Rust: Make function trait syntax without return type default to unit

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This commit is contained in:
Simon Friis Vindum
2026-01-09 16:08:01 +01:00
parent d45269609a
commit 41921a85bb
3 changed files with 30 additions and 12 deletions
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38
rust/ql/lib/codeql/rust/internal/TypeMention.qll
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@@ -222,6 +222,33 @@ class NonAliasPathTypeMention extends PathTypeMention {
result = this.getPositionalTypeArgument(pragma[only_bind_into](i), path) and
tp = this.resolveRootType().getPositionalTypeParameter(pragma[only_bind_into](i))
)
or
// Handle the special syntactic sugar for function traits. The syntactic
// form is detected by the presence of a parenthesized argument list which
// is a mandatory part of the syntax [1].
//
// For now we only support `FnOnce` as we can't support the "inherited"
// associated types of `Fn` and `FnMut` yet.
//
// [1]: https://doc.rust-lang.org/reference/paths.html#grammar-TypePathFn
exists(FnOnceTrait t, PathSegment s |
t = resolved and
s = this.getSegment() and
s.hasParenthesizedArgList()
|
tp = TTypeParamTypeParameter(t.getTypeParam()) and
result = s.getParenthesizedArgList().(TypeMention).resolveTypeAt(path)
or
tp = TAssociatedTypeTypeParameter(t.getOutputType()) and
(
result = s.getRetType().getTypeRepr().(TypeMention).resolveTypeAt(path)
or
// When the `-> ...` return type is omitted, it defaults to `()`.
not s.hasRetType() and
result instanceof UnitType and
path.isEmpty()
)
)
}
pragma[nomagic]
@@ -256,17 +283,6 @@ class NonAliasPathTypeMention extends PathTypeMention {
result = alias.getTypeRepr() and
tp = TAssociatedTypeTypeParameter(this.getResolvedAlias(pragma[only_bind_into](name)))
)
or
// Handle the special syntactic sugar for function traits. For now we only
// support `FnOnce` as we can't support the "inherited" associated types of
// `Fn` and `FnMut` yet.
exists(FnOnceTrait t | t = resolved |
tp = TTypeParamTypeParameter(t.getTypeParam()) and
result = this.getSegment().getParenthesizedArgList()
or
tp = TAssociatedTypeTypeParameter(t.getOutputType()) and
result = this.getSegment().getRetType().getTypeRepr()
)
}
pragma[nomagic]

2
rust/ql/test/library-tests/type-inference/closure.rs
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@@ -37,7 +37,7 @@ mod fn_once_trait {
}
fn return_type_omitted<F: FnOnce(bool)>(f: F) {
let _return = f(true); // $ MISSING: type=_return:()
let _return = f(true); // $ type=_return:()
}
fn argument_type<F: FnOnce(bool) -> i64>(f: F) {

2
rust/ql/test/library-tests/type-inference/type-inference.expected
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@@ -4982,7 +4982,9 @@ inferType
| closure.rs:36:25:36:28 | true | | {EXTERNAL LOCATION} | bool |
| closure.rs:39:45:39:45 | f | | closure.rs:39:28:39:42 | F |
| closure.rs:39:51:41:5 | { ... } | | {EXTERNAL LOCATION} | () |
| closure.rs:40:13:40:19 | _return | | {EXTERNAL LOCATION} | () |
| closure.rs:40:23:40:23 | f | | closure.rs:39:28:39:42 | F |
| closure.rs:40:23:40:29 | f(...) | | {EXTERNAL LOCATION} | () |
| closure.rs:40:25:40:28 | true | | {EXTERNAL LOCATION} | bool |
| closure.rs:43:46:43:46 | f | | closure.rs:43:22:43:43 | F |
| closure.rs:43:52:46:5 | { ... } | | {EXTERNAL LOCATION} | () |