Swift: clean up VarDecl, NamedPattern and SwitchStmt interactions

* `variables` under `CaseStmt` are now AST children, which solves
  orphan `VarDecl`s in that case
* reordered `CaseStmt` AST children to be `labels > variables > body`
  (was `body > labels`)
* made `NamedPattern::getVarDecl` an extracted property instead of
  `getName`
* The above led to duplicate DB entities because of a quirk in the
  Swift compiler code. This is solved by tweaking the extraction of
  `variables` under `CaseStmt` to not use `getCaseBodyVariables`.

Author: redsun82

swift/extractor/translators/PatternTranslator.cpp

@@ -4,7 +4,7 @@ namespace codeql {
 
 codeql::NamedPattern PatternTranslator::translateNamedPattern(const swift::NamedPattern& pattern) {
   auto entry = dispatcher.createEntry(pattern);
-  entry.name = pattern.getNameStr().str();
+  entry.var_decl = dispatcher.fetchLabel(pattern.getDecl());
   return entry;
 }
 

swift/extractor/translators/StmtTranslator.cpp

@@ -73,7 +73,7 @@ codeql::ForEachStmt StmtTranslator::translateForEachStmt(const swift::ForEachStm
   auto entry = dispatcher.createEntry(stmt);
   fillLabeledStmt(stmt, entry);
   entry.body = dispatcher.fetchLabel(stmt.getBody());
- // entry.sequence = dispatcher.fetchLabel(stmt.getTypeCheckedSequence());
+  // entry.sequence = dispatcher.fetchLabel(stmt.getTypeCheckedSequence());
   entry.pattern = dispatcher.fetchLabel(stmt.getPattern());
   entry.iteratorVar = dispatcher.fetchLabel(stmt.getIteratorVar());
   entry.where = dispatcher.fetchOptionalLabel(stmt.getWhere());
@@ -133,12 +133,17 @@ codeql::DoCatchStmt StmtTranslator::translateDoCatchStmt(const swift::DoCatchStm
 
 codeql::CaseStmt StmtTranslator::translateCaseStmt(const swift::CaseStmt& stmt) {
   auto entry = dispatcher.createEntry(stmt);
+  auto labels = stmt.getCaseLabelItems();
   entry.body = dispatcher.fetchLabel(stmt.getBody());
-  entry.labels = dispatcher.fetchRepeatedLabels(stmt.getCaseLabelItems());
-  if (stmt.hasCaseBodyVariables()) {
-    for (auto var : stmt.getCaseBodyVariables()) {
-      entry.variables.push_back(dispatcher.fetchLabel(var));
-    }
+  entry.labels = dispatcher.fetchRepeatedLabels(labels);
+  // we don't use stmt.getCaseBodyVariables() because it's actually filled with copies of the
+  // variable declarations, which would lead to duplicate `DeclVar` entities.
+  // Instead we follow the same logic that's used to fill getCaseBodyVariables, looking at the first
+  // pattern and collecting variables from it. See
+  // https://github.com/apple/swift/blob/71fff6649b3ce57cc22954f141cf8b567be6de88/lib/Parse/ParseStmt.cpp#L2210
+  if (!labels.empty() && labels.front().getPattern()) {
+    labels.front().getPattern()->forEachVariable(
+        [&](const swift::VarDecl* var) { entry.variables.push_back(dispatcher.fetchLabel(var)); });
   }
   return entry;
 }

swift/ql/.generated.list

@@ -9,19 +9,16 @@ private import codeql.swift.elements.decl.VarDecl
  */
 class NamedPattern extends Generated::NamedPattern {
   /**
-   * Holds if this named pattern has a corresponding `VarDecl`.
-   * This will be the case as long as the variable is subsequently used.
+   * Holds if this named pattern has a corresponding `VarDecl`, which is currently always true.
+   *
+   * DEPRECATED: unless there was a compilation error, this will always hold.
    */
-  predicate hasVarDecl() { exists(this.getVarDecl()) }
+  deprecated predicate hasVarDecl() { exists(this.getVarDecl()) }
 
   /**
-   * Gets the `VarDecl` bound by this named pattern, if any.
-   * This will be the case as long as the variable is subsequently used.
+   * Gets the name of the variable bound by this pattern.
    */
-  VarDecl getVarDecl() {
-    this.getImmediateEnclosingPattern*() = result.getImmediateParentPattern() and
-    pragma[only_bind_out](result.getName()) = pragma[only_bind_out](this.getName())
-  }
+  string getName() { result = this.getVarDecl().getName() }
 
   override string toString() { result = this.getName() }
 }