False errors due to scope condition being set incorrectly when doing Sema lookup

[mayshukla]

For example:

namespace foo {
  template <typename T>
  void bar() {}
}

void baz() {
#ifdef A
  int var=0;
  for( unsigned i=0; i<10; ++i ) {
    if (i)
      ++var;
  }
#endif
}

Produces errors:

scope_error_after_template.cpp:10:9: error: i is not defined in context ~A
    if (i)
        ^
scope_error_after_template.cpp:11:9: error: var is not defined in context ~A
      ++var;
        ^

These errors are emitted because the scope condition is sometimes set to True when it should be A. This causes Sema to report that the variable's declaration doesn't cover the entire lookup space.

[mayshukla]

Update: this bug is caused by caching of old Scope objects. When the parser enters the if statement, it uses a cached Scope object which had a condition of True. Since this condition is not reset, Sema lookup is being done from context True instead of context A. This caused Sema to find that the declarations of i and var did not cover the entire lookup space.

This issue can be fixed by properly initializing cached Scope objects after they are retrieved from the cache. The method Scope::Init can be modified to set the Condition field of the current Scope to the Condition of the parent scope.