Unexpected Fortran compiler behavior on variable declarations.

Question

There are several problems concerning Sun Fortran compiler for Linux, concerning variable declarations:
(1) A variable can be declared two or more times within the same
program scope. Surprisingly, the compiler accepts this, without any error or
warning message. This is clearly a bug.
(2) There is no warning message if a variable is used but never set, even if the -w4 flag is used. This is a serious bug.
(3) There is no warning message if a variable is declared but never
used.
To illustrate the bugs, compile the following simple program:
module fooModule
implicit none
public :: add
contains
function add(x,y)
real, intent(in) :: x,y
real :: unused ! This variable is never used and never set; no warning message.
real :: add
add=x+y
end function add
end module fooModule
program TryProg
use fooModule
implicit none
real :: x
integer :: i
integer :: i ! Duplicated declaration. The compiler accepts this!
i=3
print*,i
print*,add(x,2.0) ! Variable x is used but not set; no warning message.
end program TryProg
EXPECTED BEHAVIOR:
(1) Something like "ERROR: Duplicate declaration of 'i'" or "ERROR:
Symbol 'i' already has basic type of INTEGER."
(2) WARNING: Variable 'x' is used but not set.
(3) WARNING: Variable 'unused' is never used and never set.
ACTUAL BEHAVIOR:
No error or warning messages; expected one error and two warnings.
The bugs appear in all Fortran compilers for Linux, including latest release, SSX2.

Answer 1

There are several problems concerning Sun Fortran
compiler for Linux, concerning variable
declarations:
(1) A variable can be declared two or more times
within the same
program scope. Surprisingly, the compiler accepts
this, without any error or
warning message. This is clearly a bug.
The bugs appear in all Fortran compilers for Linux,
including latest release, SSX2.You have cited a number of constraint violations. The
Fortran standard states
A processor conforms to this standard if
(3) It contains the capability to detect and report the
use within a sumitted program unit of an
additional form or relationship that is not
permitted by the numbered syntax rules or
constraints, including the deleted features
described in Annex B;
In English, this statement means that a conforming
implementation must be able to detect and report
syntax errors and constraint violations. It does not
mean that it must detect and report them by default.
Sun f95, like most other Fortran compilers, does not
give errors or warnings for the use of common
extensions by default. The option -ansi enables
the compilation mode that reports such uses.
For example, when I compile the program
PROGRAM MAIN
REAL X
REAL X
END
with the option -ansi, I get
REAL X
^
"t.f", Line = 2, Column = 1: ANSI: Use of the tab character is an extension of the Fortran standard.
REAL X
^
"t.f", Line = 3, Column = 7: ANSI: "X" has been given the REAL attribute more than once. This is nonstandard.
f90comp: 4 SOURCE LINES
f90comp: 0 ERRORS, 0 WARNINGS, 0 OTHER MESSAGES, 2 ANSI
The caret lines up with the identifer X in the output. The column
number is given as column 7, because the letter X is the seventh
character in the line.