Swift: enhance PrintAst testing

The `ParentChild` tests have been generalized to test all `PrintAst`
by factoring out `PrintAstNode` into a separate file.

The `child.ql` and `parent.ql` tests have been removed as they are
subsumed by `PrintAst.ql`. Also, a new `no_parent_child_loops` is
added to detect back edges to a root node (back edges to a non-root
node are already detected by `no_double_parents.ql`).

Author: redsun82

swift/ql/lib/codeql/swift/printast/PrintAst.qll

@@ -2,87 +2,7 @@
  * Provides queries to pretty-print a Go AST as a graph.
  */
 
-import swift
-import codeql.swift.generated.ParentChild
-
-private newtype TPrintAstConfiguration = TMakePrintAstConfiguration()
-
-/**
- * The hook to customize the files and functions printed by this module.
- */
-class PrintAstConfiguration extends TPrintAstConfiguration {
-  /**
-   * Gets the string representation of this singleton
-   */
-  string toString() { result = "PrintAstConfiguration" }
-
-  /**
-   * Holds if the AST for `e` should be printed. By default, holds for all.
-   */
-  predicate shouldPrint(Locatable e) { any() }
-}
-
-private predicate shouldPrint(Locatable e) { any(PrintAstConfiguration config).shouldPrint(e) }
-
-/**
- * An AST node that should be printed.
- */
-private newtype TPrintAstNode =
-  TLocatable(Locatable ast) {
-    // Only consider resolved nodes (that is not within the hidden conversion AST)
-    ast = ast.resolve()
-  }
-
-/**
- * A node in the output tree.
- */
-class PrintAstNode extends TPrintAstNode {
-  /**
-   * Gets a textual representation of this node.
-   */
-  abstract string toString();
-
-  /**
-   * Gets the child node at index `index`. Child indices must be unique,
-   * but need not be contiguous.
-   */
-  abstract predicate hasChild(PrintAstNode child, int index, string accessor);
-
-  /**
-   * Holds if this node should be printed in the output.
-   */
-  abstract predicate shouldBePrinted();
-
-  /**
-   * Gets the location of this node in the source code.
-   */
-  abstract Location getLocation();
-
-  /**
-   * Gets the value of an additional property of this node, where the name of
-   * the property is `key`.
-   */
-  string getProperty(string key) { none() }
-}
-
-/**
- * A graph node representing a real Locatable node.
- */
-class PrintLocatable extends PrintAstNode, TLocatable {
-  Locatable ast;
-
-  PrintLocatable() { this = TLocatable(ast) }
-
-  final override predicate shouldBePrinted() { shouldPrint(ast) }
-
-  override predicate hasChild(PrintAstNode child, int index, string accessor) {
-    child = TLocatable(getChildAndAccessor(ast, index, accessor))
-  }
-
-  override string toString() { result = "[" + concat(ast.getPrimaryQlClasses(), ", ") + "] " + ast }
-
-  final override Location getLocation() { result = ast.getLocation() }
-}
+import PrintAstNode
 
 cached
 private int getOrder(PrintAstNode node) {

swift/ql/lib/codeql/swift/printast/PrintAstNode.qll

@@ -0,0 +1,86 @@
+/**
+ * Provides classes used to pretty-print a Go AST as a graph.
+ * This is factored out of `PrintAst.qll` for testing purposes.
+ */
+
+import swift
+import codeql.swift.generated.ParentChild
+
+private newtype TPrintAstConfiguration = TMakePrintAstConfiguration()
+
+/**
+ * The hook to customize the files and functions printed by this module.
+ */
+class PrintAstConfiguration extends TPrintAstConfiguration {
+  /**
+   * Gets the string representation of this singleton
+   */
+  string toString() { result = "PrintAstConfiguration" }
+
+  /**
+   * Holds if the AST for `e` should be printed. By default, holds for all.
+   */
+  predicate shouldPrint(Locatable e) { any() }
+}
+
+private predicate shouldPrint(Locatable e) { any(PrintAstConfiguration config).shouldPrint(e) }
+
+/**
+ * An AST node that should be printed.
+ */
+private newtype TPrintAstNode =
+  TLocatable(Locatable ast) {
+    // Only consider resolved nodes (that is not within the hidden conversion AST)
+    ast = ast.resolve()
+  }
+
+/**
+ * A node in the output tree.
+ */
+class PrintAstNode extends TPrintAstNode {
+  /**
+   * Gets a textual representation of this node.
+   */
+  abstract string toString();
+
+  /**
+   * Gets the child node at index `index`. Child indices must be unique,
+   * but need not be contiguous.
+   */
+  abstract predicate hasChild(PrintAstNode child, int index, string accessor);
+
+  /**
+   * Holds if this node should be printed in the output.
+   */
+  abstract predicate shouldBePrinted();
+
+  /**
+   * Gets the location of this node in the source code.
+   */
+  abstract Location getLocation();
+
+  /**
+   * Gets the value of an additional property of this node, where the name of
+   * the property is `key`.
+   */
+  string getProperty(string key) { none() }
+}
+
+/**
+ * A graph node representing a real Locatable node.
+ */
+class PrintLocatable extends PrintAstNode, TLocatable {
+  Locatable ast;
+
+  PrintLocatable() { this = TLocatable(ast) }
+
+  final override predicate shouldBePrinted() { shouldPrint(ast) }
+
+  override predicate hasChild(PrintAstNode child, int index, string accessor) {
+    child = TLocatable(getChildAndAccessor(ast, index, accessor))
+  }
+
+  override string toString() { result = "[" + concat(ast.getPrimaryQlClasses(), ", ") + "] " + ast }
+
+  final override Location getLocation() { result = ast.getLocation() }
+}