Rust: Handle Deref trait in type inference and data flow

rust/ql/lib/change-notes/2026-01-07-method-resolution-deref-trait.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The `Deref` trait is now considered during method resolution. This means that method calls on receivers implementing the `Deref` trait will correctly resolve to methods defined on the target type. This may result in additional query results, especially for data flow queries.

rust/ql/lib/codeql/rust/dataflow/internal/Content.qll

@@ -35,6 +35,9 @@ class TupleFieldContent extends FieldContent, TTupleFieldContent {
     not field = any(TupleType tt).getATupleField()
   }
 
+  /** Gets the tuple field. */
+  TupleField getField() { result = field }
+
   /** Holds if this field belongs to an enum variant. */
   predicate isVariantField(Variant v, int pos) { field.isVariantField(v, pos) }
 
@@ -68,6 +71,9 @@ class StructFieldContent extends FieldContent, TStructFieldContent {
 
   StructFieldContent() { this = TStructFieldContent(field) }
 
+  /** Gets the struct field. */
+  StructField getField() { result = field }
+
   /** Holds if this field belongs to an enum variant. */
   predicate isVariantField(Variant v, string name) { field.isVariantField(v, name) }
 
@@ -253,10 +259,32 @@ final class OptionalBarrier extends ContentSet, TOptionalBarrier {
 
 private import codeql.rust.internal.CachedStages
 
+string tupleFieldApprox(TupleField field) {
+  exists(Name name |
+    name = any(Variant v | field.isVariantField(v, _)).getName()
+    or
+    name = any(Struct s | field.isStructField(s, _)).getName()
+  |
+    result = name.getText().charAt(0)
+  )
+}
+
+string structFieldApprox(StructField field) {
+  exists(string name |
+    field.isVariantField(_, name) or
+    field.isStructField(_, name)
+  |
+    result = name.charAt(0)
+  )
+}
+
 cached
 newtype TContent =
-  TTupleFieldContent(TupleField field) { Stages::DataFlowStage::ref() } or
-  TStructFieldContent(StructField field) or
+  TTupleFieldContent(TupleField field) {
+    Stages::DataFlowStage::ref() and
+    exists(tupleFieldApprox(field))
+  } or
+  TStructFieldContent(StructField field) { exists(structFieldApprox(field)) } or
   TElementContent() or
   TFutureContent() or
   TTuplePositionContent(int pos) {
@@ -272,3 +300,41 @@ newtype TContent =
   } or
   TCapturedVariableContent(VariableCapture::CapturedVariable v) or
   TReferenceContent()
+
+cached
+newtype TContentApprox =
+  TTupleFieldContentApprox(string s) { Stages::DataFlowStage::ref() and s = tupleFieldApprox(_) } or
+  TStructFieldContentApprox(string s) { s = structFieldApprox(_) } or
+  TElementContentApprox() or
+  TFutureContentApprox() or
+  TTuplePositionContentApprox() or
+  TFunctionCallReturnContentApprox() or
+  TFunctionCallArgumentContentApprox() or
+  TCapturedVariableContentApprox() or
+  TReferenceContentApprox()
+
+final class ContentApprox extends TContentApprox {
+  /** Gets a textual representation of this element. */
+  string toString() {
+    exists(string s |
+      this = TTupleFieldContentApprox(s) or
+      this = TStructFieldContentApprox(s)
+    |
+      result = s
+    )
+    or
+    this = TElementContentApprox() and result = "element"
+    or
+    this = TFutureContentApprox() and result = "future"
+    or
+    this = TTuplePositionContentApprox() and result = "tuple.position"
+    or
+    this = TFunctionCallReturnContentApprox() and result = "function.return"
+    or
+    this = TFunctionCallArgumentContentApprox() and result = "function.argument"
+    or
+    this = TCapturedVariableContentApprox() and result = "captured.variable"
+    or
+    this = TReferenceContentApprox() and result = "&ref"
+  }
+}

rust/ql/lib/codeql/rust/dataflow/internal/DataFlowImpl.qll

@@ -15,6 +15,8 @@ private import codeql.rust.internal.PathResolution
 private import codeql.rust.controlflow.ControlFlowGraph
 private import codeql.rust.dataflow.Ssa
 private import codeql.rust.dataflow.FlowSummary
+private import codeql.rust.internal.TypeInference as TypeInference
+private import codeql.rust.internal.typeinference.DerefChain
 private import Node
 private import Content
 private import FlowSummaryImpl as FlowSummaryImpl
@@ -60,6 +62,10 @@ final class DataFlowCall extends TDataFlowCall {
   /** Gets the underlying call, if any. */
   Call asCall() { this = TCall(result) }
 
+  predicate isImplicitDerefCall(AstNode n, DerefChain derefChain, int i, Function target) {
+    this = TImplicitDerefCall(n, derefChain, i, target)
+  }
+
   predicate isSummaryCall(
     FlowSummaryImpl::Public::SummarizedCallable c, FlowSummaryImpl::Private::SummaryNode receiver
   ) {
@@ -69,12 +75,20 @@ final class DataFlowCall extends TDataFlowCall {
   DataFlowCallable getEnclosingCallable() {
     result.asCfgScope() = this.asCall().getEnclosingCfgScope()
     or
+    result.asCfgScope() =
+      any(AstNode n | this.isImplicitDerefCall(n, _, _, _)).getEnclosingCfgScope()
+    or
     this.isSummaryCall(result.asSummarizedCallable(), _)
   }
 
   string toString() {
     result = this.asCall().toString()
     or
+    exists(AstNode n, DerefChain derefChain, int i |
+      this.isImplicitDerefCall(n, derefChain, i, _) and
+      result = "[implicit deref call " + i + " in " + derefChain.toString() + "] " + n
+    )
+    or
     exists(
       FlowSummaryImpl::Public::SummarizedCallable c, FlowSummaryImpl::Private::SummaryNode receiver
     |
@@ -83,7 +97,11 @@ final class DataFlowCall extends TDataFlowCall {
     )
   }
 
-  Location getLocation() { result = this.asCall().getLocation() }
+  Location getLocation() {
+    result = this.asCall().getLocation()
+    or
+    result = any(AstNode n | this.isImplicitDerefCall(n, _, _, _)).getLocation()
+  }
 }
 
 /**
@@ -257,6 +275,8 @@ private module Aliases {
 
   class ContentAlias = Content;
 
+  class ContentApproxAlias = ContentApprox;
+
   class ContentSetAlias = ContentSet;
 
   class LambdaCallKindAlias = LambdaCallKind;
@@ -383,7 +403,8 @@ module RustDataFlow implements InputSig<Location> {
     node.(FlowSummaryNode).getSummaryNode().isHidden() or
     node instanceof CaptureNode or
     node instanceof ClosureParameterNode or
-    node instanceof DerefBorrowNode or
+    node instanceof ImplicitDerefNode or
+    node instanceof ImplicitBorrowNode or
     node instanceof DerefOutNode or
     node instanceof IndexOutNode or
     node.asExpr() instanceof ParenExpr or
@@ -445,6 +466,12 @@ module RustDataFlow implements InputSig<Location> {
       or
       result.asSummarizedCallable() = getStaticTargetExt(c)
     )
+    or
+    exists(Function f | call = TImplicitDerefCall(_, _, _, f) |
+      result.asCfgScope() = f
+      or
+      result.asSummarizedCallable() = f
+    )
   }
 
   /**
@@ -471,9 +498,27 @@ module RustDataFlow implements InputSig<Location> {
 
   predicate forceHighPrecision(Content c) { none() }
 
-  final class ContentApprox = Content; // TODO: Implement if needed
+  class ContentApprox = ContentApproxAlias;
 
-  ContentApprox getContentApprox(Content c) { result = c }
+  ContentApprox getContentApprox(Content c) {
+    result = TTupleFieldContentApprox(tupleFieldApprox(c.(TupleFieldContent).getField()))
+    or
+    result = TStructFieldContentApprox(structFieldApprox(c.(StructFieldContent).getField()))
+    or
+    result = TElementContentApprox() and c instanceof ElementContent
+    or
+    result = TFutureContentApprox() and c instanceof FutureContent
+    or
+    result = TTuplePositionContentApprox() and c instanceof TuplePositionContent
+    or
+    result = TFunctionCallArgumentContentApprox() and c instanceof FunctionCallArgumentContent
+    or
+    result = TFunctionCallReturnContentApprox() and c instanceof FunctionCallReturnContent
+    or
+    result = TCapturedVariableContentApprox() and c instanceof CapturedVariableContent
+    or
+    result = TReferenceContentApprox() and c instanceof ReferenceContent
+  }
 
   /**
    * Holds if the parameter position `ppos` matches the argument position
@@ -499,6 +544,8 @@ module RustDataFlow implements InputSig<Location> {
         not FlowSummaryImpl::Private::Steps::prohibitsUseUseFlow(nodeFrom, _)
       )
       or
+      nodeFrom = nodeTo.(ImplicitDerefNode).getLocalInputNode()
+      or
       VariableCapture::localFlowStep(nodeFrom, nodeTo)
     ) and
     model = ""
@@ -524,16 +571,14 @@ module RustDataFlow implements InputSig<Location> {
   }
 
   pragma[nomagic]
-  private predicate implicitDeref(Node node1, DerefBorrowNode node2, ReferenceContent c) {
-    not node2.isBorrow() and
-    node1.asExpr() = node2.getNode() and
+  private predicate implicitDeref(ImplicitDerefNode node1, Node node2, ReferenceContent c) {
+    node2 = node1.getDerefOutputNode() and
     exists(c)
   }
 
   pragma[nomagic]
-  private predicate implicitBorrow(Node node1, DerefBorrowNode node2, ReferenceContent c) {
-    node2.isBorrow() and
-    node1.asExpr() = node2.getNode() and
+  private predicate implicitBorrow(Node node1, ImplicitDerefBorrowNode node2, ReferenceContent c) {
+    node1 = node2.getBorrowInputNode() and
     exists(c)
   }
 
@@ -545,10 +590,10 @@ module RustDataFlow implements InputSig<Location> {
 
   private Node getFieldExprContainerNode(FieldExpr fe) {
     exists(Expr container | container = fe.getContainer() |
-      not any(DerefBorrowNode n).getNode() = container and
+      not TypeInference::implicitDerefChainBorrow(container, _, _) and
       result.asExpr() = container
       or
-      result.(DerefBorrowNode).getNode() = container
+      result.(ImplicitDerefNode).isLast(container)
     )
   }
 
@@ -1037,6 +1082,10 @@ private module Cached {
       Stages::DataFlowStage::ref() and
       call.hasEnclosingCfgScope()
     } or
+    TImplicitDerefCall(AstNode n, DerefChain derefChain, int i, Function target) {
+      TypeInference::implicitDerefChainBorrow(n, derefChain, _) and
+      target = derefChain.getElement(i).getDerefFunction()
+    } or
     TSummaryCall(
       FlowSummaryImpl::Public::SummarizedCallable c, FlowSummaryImpl::Private::SummaryNode receiver
     ) {