Merge pull request github#3259 from MathiasVP/ql-doc-fileclosed-loopbounds-memoryfreed

C++: QLDoc for FileClosed, LoopBounds and MemoryFreed

Author: jbj

cpp/ql/src/Critical/FileClosed.qll

@@ -1,5 +1,6 @@
 import semmle.code.cpp.pointsto.PointsTo
 
+/** Holds if there exists a call to a function that might close the file specified by `e`. */
 predicate closed(Expr e) {
   fcloseCall(_, e) or
   exists(ExprCall c |
@@ -8,10 +9,19 @@ predicate closed(Expr e) {
   )
 }
 
+/** An expression for which there exists a function call that might close it. */
 class ClosedExpr extends PointsToExpr {
   ClosedExpr() { closed(this) }
 
   override predicate interesting() { closed(this) }
 }
 
+/**
+ * Holds if `fc` is a call to a function that opens a file that might be closed. For example:
+ * ```
+ * FILE* f = fopen("file.txt", "r");
+ * ...
+ * fclose(f);
+ * ```
+ */
 predicate fopenCallMayBeClosed(FunctionCall fc) { fopenCall(fc) and anythingPointsTo(fc) }

cpp/ql/src/Critical/LoopBounds.qll

@@ -2,12 +2,24 @@
 
 import cpp
 
+/**
+ * An assignment to a variable with the value `0`. For example:
+ * ```
+ * int x;
+ * x = 0;
+ * ```
+ * but not:
+ * ```
+ * int x = 0;
+ * ```
+ */
 class ZeroAssignment extends AssignExpr {
   ZeroAssignment() {
     this.getAnOperand() instanceof VariableAccess and
     this.getAnOperand() instanceof Zero
   }
 
+  /** Gets a variable that is assigned the value `0`. */
   Variable assignedVariable() { result.getAnAccess() = this.getAnOperand() }
 }
 

cpp/ql/src/Critical/MemoryFreed.qll

@@ -9,10 +9,19 @@ private predicate freed(Expr e) {
   )
 }
 
+/** An expression that might be deallocated. */
 class FreedExpr extends PointsToExpr {
   FreedExpr() { freed(this) }
 
   override predicate interesting() { freed(this) }
 }
 
+/**
+ * An allocation expression that might be deallocated. For example:
+ * ```
+ * int* p = new int;
+ * ...
+ * delete p;
+ * ```
+ */
 predicate allocMayBeFreed(AllocationExpr alloc) { anythingPointsTo(alloc) }