JS: Mark type-annotated nodes as SourceNode

javascript/ql/lib/semmle/javascript/dataflow/Sources.qll

@@ -333,7 +333,13 @@ module SourceNode {
         astNode instanceof TaggedTemplateExpr or
         astNode instanceof Templating::PipeRefExpr or
         astNode instanceof Templating::TemplateVarRefExpr or
-        astNode instanceof StringLiteral
+        astNode instanceof StringLiteral or
+        astNode instanceof TypeAssertion
+      )
+      or
+      exists(VariableDeclarator decl |
+        exists(decl.getTypeAnnotation()) and
+        this = DataFlow::valueNode(decl.getBindingPattern())
       )
       or
       DataFlow::parameterNode(this, _)

javascript/ql/lib/semmle/javascript/internal/TypeResolution.qll

@@ -189,7 +189,12 @@ module TypeResolution {
     )
   }
 
-  private predicate contextualType(Node value, Node type) {
+  predicate contextualType(Node value, Node type) {
+    exists(LocalVariable v |
+      type = v.getADeclaration().getTypeAnnotation() and
+      value = v.getAnAssignedExpr()
+    )
+    or
     exists(InvokeExpr call, Function target, int i |
       callTarget(call, target) and
       value = call.getArgument(i) and
@@ -228,6 +233,8 @@ module TypeResolution {
   predicate valueHasType(Node value, Node type) {
     value.(BindingPattern).getTypeAnnotation() = type
     or
+    value.(TypeAssertion).getTypeAnnotation() = type
+    or
     exists(VarDecl decl |
       // ValueFlow::step is restricted to variables with at most one assignment. Allow the type annotation
       // of a variable to propagate to its uses, even if the variable has multiple assignments.