Move getExpr to SwitchExpr

Author: owen-mc

go/ql/lib/semmle/go/Stmt.qll

@@ -832,6 +832,12 @@ class SwitchStmt extends @switchstmt, Stmt, ScopeNode {
   /** Gets the init statement of this `switch` statement, if any. */
   Stmt getInit() { result = this.getChildStmt(0) }
 
+  /**
+   * Gets the expression whose value or type is examined by this `switch`
+   * statement, if any.
+   */
+  Expr getExpr() { none() }
+
   /** Gets the body of this `switch` statement. */
   BlockStmt getBody() { result = this.getChildStmt(2) }
 
@@ -880,8 +886,7 @@ class SwitchStmt extends @switchstmt, Stmt, ScopeNode {
  * ```
  */
 class ExpressionSwitchStmt extends @exprswitchstmt, SwitchStmt {
-  /** Gets the switch expression of this `switch` statement. */
-  Expr getExpr() { result = this.getChildExpr(1) }
+  override Expr getExpr() { result = this.getChildExpr(1) }
 
   override predicate mayHaveSideEffects() {
     this.getInit().mayHaveSideEffects() or
@@ -912,14 +917,13 @@ class ExpressionSwitchStmt extends @exprswitchstmt, SwitchStmt {
  * ```
  */
 class TypeSwitchStmt extends @typeswitchstmt, SwitchStmt {
-  /** Gets the assign statement of this type-switch statement. */
   SimpleAssignStmt getAssign() { result = this.getChildStmt(1) }
 
   /** Gets the test statement of this type-switch statement. This is a `SimpleAssignStmt` or `ExprStmt`. */
   Stmt getTest() { result = this.getChildStmt(1) }
 
   /** Gets the expression whose type is examined by this `switch` statement. */
-  Expr getExpr() {
+  override Expr getExpr() {
     result = this.getAssign().getRhs() or result = this.getChildStmt(1).(ExprStmt).getExpr()
   }
 

go/ql/lib/semmle/go/controlflow/ControlFlowGraphShared.qll

@@ -265,15 +265,7 @@ module CfgImpl {
     }
 
     class Switch extends AstNode instanceof Go::SwitchStmt {
-      Expr getExpr() {
-        result = this.(Go::ExpressionSwitchStmt).getExpr()
-        or
-        // For a type switch the "switch expression" is the type-assertion
-        // expression `x.(type)`; evaluating it directly (rather than the
-        // wrapping `y := x.(type)` statement) lets the shared switch model
-        // drive the per-case type tests.
-        result = this.(Go::TypeSwitchStmt).getExpr()
-      }
+      Expr getExpr() { result = this.(Go::SwitchStmt).getExpr() }
 
       Case getCase(int index) { result = this.(Go::SwitchStmt).getCase(index) }