[flang] Catch more initialization errors
Diagnose some error cases related to initialization that are
slipping past semantic checking: don't allow multiple initializations
of the same symbol, and don't allow an object that was initialized
as a scalar to become an array afterward.
Fixes llvm-test-suite/Fortran/gfortran/regression/initialization_17.f90.
Initializers in entity-decls don't need to have their expressions
analyzed immediately in name resolution unless of course they are
defining the values of named constants. By deferring the expression
analysis, the compiler can better handle references to module and
internal procedures that might appear in structure constructors; at
present, these are typically rejected as being forward references (which
they can be) to subprogram names that can't yet be checked for
compatibility with the characteristics of the corresponding procedure
component.
Before emitting a warning message, code should check that the usage in
question should be diagnosed by calling ShouldWarn(). A fair number of
sites in the code do not, and can emit portability warnings
unconditionally, which can confuse a user that hasn't asked for them
(-pedantic) and isn't terribly concerned about portability *to* other
compilers.
Add calls to ShouldWarn() or IsEnabled() around messages that need them,
and add -pedantic to tests that now require it to test their portability
messages, and add more expected message lines to those tests when
-pedantic causes other diagnostics to fire.
Most attributes apply to only object or only procedure entities,
and attempts to apply them to other kinds of symbol table entries
are caught in name resolution when ConvertToObjectEntity() or
ConvertToProcEntity() fails. However, the POINTER attribute can
be applied to both, and name resolution can't perform that conversion
yet, and as a result we don't catch many kinds of silly errors.
Fix by ensuring that the symbol is of a type that could eventually
become an object or procedure entity if it is not one already.
Differential Revision: https://reviews.llvm.org/D140137
