From cb678e370e383de27f81fc16935a76f3f2d2f110 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9a=20Saviot?= <lea.saviot@numworks.com>
Date: Thu, 8 Nov 2018 15:12:02 +0100
Subject: [PATCH] [poincare] Escape when recursion too deep

---
 poincare/include/poincare/expression.h |  9 +++
 poincare/src/expression.cpp            | 79 +++++++++++++++++++++++---
 poincare/src/init.cpp                  |  4 ++
 3 files changed, 84 insertions(+), 8 deletions(-)

diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index de67877cc..c4c2f2575 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -90,7 +90,11 @@ class Expression : public TreeHandle {
   friend class SymbolNode;
 
 public:
+  static void TidyAfterException() {
+    UnlockRecursionCountReset();
+  }
   static bool isExpression() { return true; }
+
   /* Constructor & Destructor */
   Expression() : TreeHandle() {}
   Expression clone() const;
@@ -253,6 +257,11 @@ protected:
 
 private:
   /* Simplification */
+  static constexpr int sRecursionLimit = 2000; //TODO value?
+  static bool ResetRecursionCountAndLockReset();
+  static void UnlockRecursionCountReset();
+  static void IncrementRecursionCount();
+  static bool RecursionMaximalDepthExceeded();
   Expression deepReduce(Context & context, Preferences::AngleUnit angleUnit, bool replaceSymbols = true);
   void deepReduceChildren(Context & context, Preferences::AngleUnit angleUnit, bool replaceSymbols) {
     return node()->deepReduceChildren(context, angleUnit, replaceSymbols);
diff --git a/poincare/src/expression.cpp b/poincare/src/expression.cpp
index b3eab228b..51798cd9e 100644
--- a/poincare/src/expression.cpp
+++ b/poincare/src/expression.cpp
@@ -13,6 +13,9 @@
 
 namespace Poincare {
 
+static int sRecursionCount = 0;
+static bool sRecursionCountReinitializationIsLocked = false;
+
 /* Constructor & Destructor */
 
 Expression Expression::clone() const { TreeHandle c = TreeHandle::clone(); return static_cast<Expression&>(c); }
@@ -75,15 +78,32 @@ bool Expression::isRationalOne() const {
 }
 
 bool Expression::recursivelyMatches(ExpressionTest test, Context & context) const {
-  if (test(*this, context)) {
-    return true;
-  }
-  for (int i = 0; i < this->numberOfChildren(); i++) {
-    if (childAtIndex(i).recursivelyMatches(test, context)) {
-      return true;
+  // Reset recursion count if needed
+  bool willHaveToUnlock = ResetRecursionCountAndLockReset();
+
+  bool result = false;
+
+  IncrementRecursionCount();
+  if (RecursionMaximalDepthExceeded()) {
+    //TODO propagate recursion error?
+  } else {
+    if (test(*this, context)) {
+      result = true;
+    } else {
+      for (int i = 0; i < this->numberOfChildren(); i++) {
+        if (childAtIndex(i).recursivelyMatches(test, context)) {
+          result = true;
+          break;
+        }
+      }
     }
   }
-  return false;
+
+  // Unlock recursion count reset if needed
+  if (willHaveToUnlock) {
+    UnlockRecursionCountReset();
+  }
+  return result;
 }
 
 bool Expression::isApproximate(Context & context) const {
@@ -223,6 +243,11 @@ void Expression::defaultSetChildrenInPlace(Expression other) {
 
 template<typename U>
 Evaluation<U> Expression::approximateToEvaluation(Context& context, Preferences::AngleUnit angleUnit) const {
+  assert(sRecursionCountReinitializationIsLocked == true);
+  IncrementRecursionCount();
+  if (RecursionMaximalDepthExceeded()) {
+    return Complex<U>::Undefined(); // TODO Propagate error "Recursion too deep"
+  }
   return node()->approximate(U(), context, angleUnit);
 }
 
@@ -309,10 +334,47 @@ Expression Expression::simplify(Context & context, Preferences::AngleUnit angleU
 }
 
 Expression Expression::reduce(Context & context, Preferences::AngleUnit angleUnit, bool replaceSymbols) {
-  return deepReduce(context, angleUnit, replaceSymbols);
+  // Reset recursion count if needed
+  bool willHaveToUnlock = ResetRecursionCountAndLockReset();
+
+  Expression result = deepReduce(context, angleUnit, replaceSymbols);
+
+  // Unlock recursion count reinitialization if needed
+  if (willHaveToUnlock) {
+    UnlockRecursionCountReset();
+  }
+
+  return result;
+}
+
+bool Expression::ResetRecursionCountAndLockReset() {
+  if (!sRecursionCountReinitializationIsLocked) {
+    sRecursionCount = 0;
+    sRecursionCountReinitializationIsLocked = true;
+    return true;
+  }
+  return false;
+}
+
+void Expression::UnlockRecursionCountReset() {
+  sRecursionCountReinitializationIsLocked = false;
+}
+
+void Expression::IncrementRecursionCount() {
+  sRecursionCount++;
+}
+
+bool Expression::RecursionMaximalDepthExceeded() {
+  return sRecursionCount >= Expression::sRecursionLimit;
 }
 
 Expression Expression::deepReduce(Context & context, Preferences::AngleUnit angleUnit, bool replaceSymbols) {
+  IncrementRecursionCount();
+  if (RecursionMaximalDepthExceeded()) {
+    sSimplificationHasBeenInterrupted = true;
+    return *this;
+  }
+
 #if MATRIX_EXACT_REDUCING
 #else
   if (IsMatrix(*this, context)) {
@@ -320,6 +382,7 @@ Expression Expression::deepReduce(Context & context, Preferences::AngleUnit angl
     return *this;
   }
 #endif
+
   deepReduceChildren(context, angleUnit, replaceSymbols);
   return shallowReduce(context, angleUnit, replaceSymbols);
 }
diff --git a/poincare/src/init.cpp b/poincare/src/init.cpp
index 338bb197b..bcaa62c1b 100644
--- a/poincare/src/init.cpp
+++ b/poincare/src/init.cpp
@@ -1,4 +1,5 @@
 #include <poincare/init.h>
+#include <poincare/expression.h>
 #include <poincare/integer.h>
 #include <poincare/tree_pool.h>
 
@@ -13,6 +14,9 @@ void Init() {
 void Tidy() {
   // Clean Integer
   Integer::TidyIntegerBuffer();
+
+  // Unlock recursion count
+  Expression::TidyAfterException();
 }
 
 }