C++: Use parameterized modules instead of abstract classes and predicates to handle debug printing.

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DebugPrinting.qll

@@ -1,9 +1,21 @@
 /**
- * This file activates debugging mode for dataflow node printing.
+ * This file contains module that implements the _debug_ version of
+ * `toString` for `Instruction` and `Operand` dataflow nodes.
  */
 
-private import Node0ToString
+private import semmle.code.cpp.ir.IR
+private import codeql.util.Unit
+private import Node0ToStringSig
+private import DataFlowUtil
 
-private class DebugNode0ToString extends Node0ToString {
-  final override predicate isDebugMode() { any() }
+private module DebugNode0ToString implements Node0ToStringSig {
+  string instructionToString(Instruction i) { result = i.getDumpString() }
+
+  string operandToString(Operand op) {
+    result = op.getDumpString() + " @ " + op.getUse().getResultId()
+  }
+
+  string toExprString(Node n) { none() }
 }
+
+import DebugNode0ToString

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/Node0ToString.qll

@@ -1,75 +1,8 @@
 /**
- * This file contains the abstract class that serves as the base class for
- * dataflow node printing.
+ * This file imports the module that is used to construct the strings used by `Node.ToString`.
  *
- * By default, a non-debug string is produced. However, a debug-friendly
- * string can be produced by importing `DebugPrinting.qll`.
+ * Normally, this file should just import `NormalNode0ToString` to compute the efficient `toString`, but for debugging purposes
+ * one can import `DebugPrinting.qll` to better correlate the dataflow nodes with their underlying instructions and operands.
  */
 
-private import semmle.code.cpp.ir.IR
-private import codeql.util.Unit
-
-/**
- * A class to control whether a debugging version of instructions and operands
- * should be printed as part of the `toString` output of dataflow nodes.
- *
- * To enable debug printing import the `DebugPrinting.ql` file. By default,
- * non-debug output will be used.
- */
-class Node0ToString extends Unit {
-  abstract predicate isDebugMode();
-
-  private string normalInstructionToString(Instruction i) {
-    not this.isDebugMode() and
-    if i.(InitializeParameterInstruction).getIRVariable() instanceof IRThisVariable
-    then result = "this"
-    else result = i.getAst().toString()
-  }
-
-  private string normalOperandToString(Operand op) {
-    not this.isDebugMode() and
-    if op.getDef().(InitializeParameterInstruction).getIRVariable() instanceof IRThisVariable
-    then result = "this"
-    else result = op.getDef().getAst().toString()
-  }
-
-  /**
-   * Gets the string that should be used by `InstructionNode.toString`
-   */
-  string instructionToString(Instruction i) {
-    if this.isDebugMode()
-    then result = i.getDumpString()
-    else result = this.normalInstructionToString(i)
-  }
-
-  /**
-   * Gets the string that should be used by `OperandNode.toString`.
-   */
-  string operandToString(Operand op) {
-    if this.isDebugMode()
-    then result = op.getDumpString() + " @ " + op.getUse().getResultId()
-    else result = this.normalOperandToString(op)
-  }
-}
-
-private class NoDebugNode0ToString extends Node0ToString {
-  final override predicate isDebugMode() { none() }
-}
-
-/**
- * Gets the string that should be used by `OperandNode.toString`.
- */
-string operandToString(Operand op) { result = any(Node0ToString nts).operandToString(op) }
-
-/**
- * Gets the string that should be used by `InstructionNode.toString`
- */
-string instructionToString(Instruction i) { result = any(Node0ToString nts).instructionToString(i) }
-
-/**
- * Holds if debugging mode is enabled.
- *
- * In debug mode the `toString` on dataflow nodes is more expensive to compute,
- * but gives more precise information about the different dataflow nodes.
- */
-predicate isDebugMode() { any(Node0ToString nts).isDebugMode() }
+import NormalNode0ToString

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/Node0ToStringSig.qll

@@ -0,0 +1,25 @@
+/**
+ * This file contains the signature module for controlling the behavior of `Node.toString`.
+ */
+
+private import semmle.code.cpp.ir.IR
+private import codeql.util.Unit
+private import DataFlowUtil
+
+/** A signature for a module to control the behavior of `Node.toString`. */
+signature module Node0ToStringSig {
+  /**
+   * Gets the string that should be used by `OperandNode.toString`.
+   */
+  string operandToString(Operand op);
+
+  /**
+   * Gets the string that should be used by `InstructionNode.toString`.
+   */
+  string instructionToString(Instruction i);
+
+  /**
+   * Gets the string representation of the `Expr` associated with `n`, if any.
+   */
+  string toExprString(Node n);
+}

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/NormalNode0ToString.qll

@@ -0,0 +1,33 @@
+/**
+ * This file contains module that implements the non-debug version of
+ * `toString` for `Instruction` and `Operand` dataflow nodes.
+ */
+
+private import semmle.code.cpp.ir.IR
+private import codeql.util.Unit
+private import Node0ToStringSig
+private import DataFlowUtil
+private import DataFlowPrivate
+
+private module NormalNode0ToStringImpl implements Node0ToStringSig {
+  string instructionToString(Instruction i) {
+    if i.(InitializeParameterInstruction).getIRVariable() instanceof IRThisVariable
+    then result = "this"
+    else result = i.getAst().toString()
+  }
+
+  string operandToString(Operand op) {
+    if op.getDef().(InitializeParameterInstruction).getIRVariable() instanceof IRThisVariable
+    then result = "this"
+    else result = op.getDef().getAst().toString()
+  }
+
+  string toExprString(Node n) {
+    result = n.asExpr(0).toString()
+    or
+    not exists(n.asExpr()) and
+    result = stars(n) + n.asIndirectExpr(0, 1).toString()
+  }
+}
+
+import NormalNode0ToStringImpl