C++: Introduce re-use expressions in the database scheme

cpp/downgrades/aa7ff0ab32cd4674f6ab731d32fea64116997b05/exprs.ql

@@ -0,0 +1,13 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class Location extends @location_expr {
+  string toString() { none() }
+}
+
+from Expr expr, int kind, int kind_new, Location loc
+where
+  exprs(expr, kind, loc) and
+  if kind = 363 then kind_new = 1 else kind_new = kind
+select expr, kind_new, loc

cpp/downgrades/aa7ff0ab32cd4674f6ab731d32fea64116997b05/upgrade.properties

@@ -0,0 +1,4 @@
+description: Introduce re-use expressions
+compatibility: partial
+expr_reuse.rel: delete
+exprs.rel: run exprs.qlo

cpp/ql/lib/semmle/code/cpp/exprs/Expr.qll

@@ -1322,3 +1322,23 @@ class CoYieldExpr extends UnaryOperation, @co_yield {
 
   override int getPrecedence() { result = 2 }
 }
+
+/**
+ * An expression representing the re-use of another expression.
+ *
+ * In some specific cases an expression may be referred to outside its
+ * original context. A re-use expression wraps any such reference. A
+ * re-use expression can for example occur as the qualifier of an implicit
+ * destructor called on a temporary object, where the original use of the
+ * expression is in the definition of the temporary.
+ */
+class ReuseExpr extends Expr, @reuseexpr {
+  override string getAPrimaryQlClass() { result = "ReuseExpr" }
+
+  override string toString() { result = "reuse of " + this.getReusedExpr().toString() }
+
+  /**
+   * Gets the expression that is being re-used.
+   */
+  Expr getReusedExpr() { expr_reuse(underlyingElement(this), unresolveElement(result)) }
+}

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -1513,6 +1513,11 @@ exprs(
     int location: @location_expr ref
 );
 
+expr_reuse(
+    int reuse: @expr ref,
+    int original: @expr ref
+)
+
 /*
   case @value.category of
     1 = prval
@@ -1741,6 +1746,7 @@ case @expr.kind of
 | 360 = @isunsigned
 | 361 = @isvoid
 | 362 = @isvolatile
+| 363 = @reuseexpr
 ;
 
 @var_args_expr = @vastartexpr

cpp/ql/lib/upgrades/298438feb146335af824002589cd6d4e96e5dbf9/upgrade.properties

@@ -0,0 +1,2 @@
+description: Introduce re-use expressions
+compatibility: backwards