Split up Aggregate properly

Previously, we had `Aggregate` and `ExprAggregate` as separate classes,
the latter of which representing aggregates that contain only an
expression.

This was a problem for the `rank` aggregate, as it inherited from
`Aggregate`, but _could_ also contain just an expression (even if this
is rather rare).

To fix this, I renamed `Aggregate` to `FullAggregate` (to make the
division clearer), and added a new type `Aggregate` that represents the
union of these two types. Now `Rank` can inherit from the new class
`Aggregate` and everything is dandy.

ql/src/codeql_ql/ast/Ast.qll

@@ -1392,11 +1392,17 @@ class HigherOrderFormula extends THigherOrderFormula, Formula {
   }
 }
 
+class Aggregate extends TAggregate, Expr {
+  string getKind() { none() }
+
+  Generated::Aggregate getAggregate() { none() }
+}
+
 /**
  * An aggregate containing an expression.
  * E.g. `min(getAPredicate().getArity())`.
  */
-class ExprAggregate extends TExprAggregate, Expr {
+class ExprAggregate extends TExprAggregate, Aggregate {
   Generated::Aggregate agg;
   Generated::ExprAggregateBody body;
   string kind;
@@ -1411,7 +1417,9 @@ class ExprAggregate extends TExprAggregate, Expr {
    * Gets the kind of aggregate.
    * E.g. for `min(foo())` the result is "min".
    */
-  string getKind() { result = kind }
+  override string getKind() { result = kind }
+
+  override Generated::Aggregate getAggregate() { result = agg }
 
   /**
    * Gets the ith "as" expression of this aggregate, if any.
@@ -1457,13 +1465,13 @@ class ExprAggregate extends TExprAggregate, Expr {
 }
 
 /** An aggregate expression, such as `count` or `sum`. */
-class Aggregate extends TAggregate, Expr {
+class FullAggregate extends TFullAggregate, Aggregate {
   Generated::Aggregate agg;
   string kind;
   Generated::FullAggregateBody body;
 
-  Aggregate() {
-    this = TAggregate(agg) and
+  FullAggregate() {
+    this = TFullAggregate(agg) and
     kind = agg.getChild(0).(Generated::AggId).getValue() and
     body = agg.getChild(_)
   }
@@ -1472,7 +1480,9 @@ class Aggregate extends TAggregate, Expr {
    * Gets the kind of aggregate.
    * E.g. for `min(int i | foo(i))` the result is "foo".
    */
-  string getKind() { result = kind }
+  override string getKind() { result = kind }
+
+  override Generated::Aggregate getAggregate() { result = agg }
 
   /** Gets the ith declared argument of this quantifier. */
   VarDecl getArgument(int i) { toGenerated(result) = body.getChild(i) }
@@ -1502,7 +1512,7 @@ class Aggregate extends TAggregate, Expr {
     result = body.getOrderBys().getChild(i).getChild(1).(Generated::Direction).getValue()
   }
 
-  override string getAPrimaryQlClass() { result = "Aggregate[" + kind + "]" }
+  override string getAPrimaryQlClass() { kind != "rank" and result = "FullAggregate[" + kind + "]" }
 
   override Type getType() {
     exists(PrimitiveType prim | prim = result |
@@ -1540,14 +1550,14 @@ class Aggregate extends TAggregate, Expr {
  * A "rank" expression, such as `rank[4](int i | i = [5 .. 15] | i)`.
  */
 class Rank extends Aggregate {
-  Rank() { kind = "rank" }
+  Rank() { this.getKind() = "rank" }
 
   override string getAPrimaryQlClass() { result = "Rank" }
 
   /**
    * The `i` in `rank[i]( | | )`.
    */
-  Expr getRankExpr() { toGenerated(result) = agg.getChild(1) }
+  Expr getRankExpr() { toGenerated(result) = this.getAggregate().getChild(1) }
 
   override AstNode getAChild(string pred) {
     result = super.getAChild(pred)

ql/src/codeql_ql/ast/internal/AstNodes.qll

@@ -21,7 +21,9 @@ newtype TAstNode =
   TComparisonFormula(Generated::CompTerm comp) or
   TComparisonOp(Generated::Compop op) or
   TQuantifier(Generated::Quantified quant) or
-  TAggregate(Generated::Aggregate agg) { agg.getChild(_) instanceof Generated::FullAggregateBody } or
+  TFullAggregate(Generated::Aggregate agg) {
+    agg.getChild(_) instanceof Generated::FullAggregateBody
+  } or
   TExprAggregate(Generated::Aggregate agg) {
     agg.getChild(_) instanceof Generated::ExprAggregateBody
   } or
@@ -63,9 +65,11 @@ class TFormula =
 
 class TBinOpExpr = TAddSubExpr or TMulDivModExpr;
 
+class TAggregate = TFullAggregate or TExprAggregate;
+
 class TExpr =
-  TBinOpExpr or TLiteral or TAggregate or TExprAggregate or TIdentifier or TInlineCast or TCall or
-      TUnaryExpr or TExprAnnotation or TDontCare or TRange or TSet or TAsExpr or TSuper;
+  TBinOpExpr or TLiteral or TAggregate or TIdentifier or TInlineCast or
+      TCall or TUnaryExpr or TExprAnnotation or TDontCare or TRange or TSet or TAsExpr or TSuper;
 
 class TCall = TPredicateCall or TMemberCall or TNoneCall or TAnyCall;
 
@@ -77,7 +81,7 @@ private Generated::AstNode toGeneratedFormula(AST::AstNode n) {
   n = TComparisonFormula(result) or
   n = TComparisonOp(result) or
   n = TQuantifier(result) or
-  n = TAggregate(result) or
+  n = TFullAggregate(result) or
   n = TIdentifier(result) or
   n = TNegation(result) or
   n = TIfFormula(result) or
@@ -94,7 +98,7 @@ private Generated::AstNode toGeneratedExpr(AST::AstNode n) {
   n = TSet(result) or
   n = TExprAnnotation(result) or
   n = TLiteral(result) or
-  n = TAggregate(result) or
+  n = TFullAggregate(result) or
   n = TExprAggregate(result) or
   n = TIdentifier(result) or
   n = TUnaryExpr(result) or

ql/src/codeql_ql/ast/internal/Variable.qll

@@ -2,7 +2,7 @@ import ql
 import codeql_ql.ast.internal.AstNodes
 
 private class TScope =
-  TClass or TAggregate or TExprAggregate or TQuantifier or TSelect or TPredicate or TNewTypeBranch;
+  TClass or TFullAggregate or TExprAggregate or TQuantifier or TSelect or TPredicate or TNewTypeBranch;
 
 /** A variable scope. */
 class VariableScope extends TScope, AstNode {
@@ -24,7 +24,7 @@ class VariableScope extends TScope, AstNode {
       or
       decl = this.(Select).getExpr(_).(AsExpr)
       or
-      decl = this.(Aggregate).getExpr(_).(AsExpr)
+      decl = this.(FullAggregate).getExpr(_).(AsExpr)
       or
       decl = this.(ExprAggregate).getExpr(_).(AsExpr)
       or