while: Restore tolerance of condition error

Since commit 880ca66b51 (Fix: `while()` can silently ignore incorrect
condition, 2021-08-09, v3.22.0-rc1~238^2~4) we correctly reject the
code

    set(paren "(")
    while(${paren})
    endwhile()

However, rejecting it breaks compatibility with projects that used such
code accidentally.  In CMake 3.21 and below, any error in the condition
was ignored because the `false` result exited the loop first.  Restore
tolerance of the error for now.  A policy will be needed to make it an
error later.

Note that the same condition with `if` was always correctly rejected.

Fixes: #22524
Issue: #23296
Co-authored-by: Brad King <brad.king@kitware.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/Source/cmWhileCommand.cxx b/Source/cmWhileCommand.cxx
index b8297ce..a93a81f 100644
--- a/Source/cmWhileCommand.cxx
+++ b/Source/cmWhileCommand.cxx
@@ -79,12 +79,17 @@ bool cmWhileFunctionBlocker::Replay(std::vector<cmListFileFunction> functions,
     return out;
   };
 
+  // FIXME(#23296): For compatibility with older versions of CMake, we
+  // tolerate condition errors that evaluate to false.  We should add
+  // a policy to enforce such errors.
+  bool enforceError = true;
   std::string errorString;
   MessageType messageType;
 
   for (cmConditionEvaluator conditionEvaluator(mf, whileBT);
-       conditionEvaluator.IsTrue(expandArgs(this->Args, expandedArguments),
-                                 errorString, messageType);) {
+       (enforceError = /* enforce condition errors that evaluate to true */
+        conditionEvaluator.IsTrue(expandArgs(this->Args, expandedArguments),
+                                  errorString, messageType));) {
     // Invoke all the functions that were collected in the block.
     for (cmListFileFunction const& fn : functions) {
       cmExecutionStatus status(mf);
@@ -105,7 +110,7 @@ bool cmWhileFunctionBlocker::Replay(std::vector<cmListFileFunction> functions,
     }
   }
 
-  if (!errorString.empty()) {
+  if (!errorString.empty() && enforceError) {
     std::string err = "had incorrect arguments:\n ";
     for (auto const& i : expandedArguments) {
       err += " ";