c++/7178: "CONST" pre-processed to "const" -- case problem (pre-processing bug)

[dobrynin at bigfoot dot com]

>Number:         7178
>Category:       c++
>Synopsis:       "CONST" pre-processed to "const" -- case problem (pre-processing bug)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          accepts-illegal
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 01 12:46:07 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Nickolai Dobrynin, University of WI-Milwaukee
>Release:        gcc version 3.1
>Organization:
>Environment:
  Windows 2000 Pro, Pentium 3, Dell Dimension

  the options given when GCC was configured/built:
    Configured with: ../gcc/configure --with-gcc --with-gnu-ld --with-gnu-as --host=
    mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable
    -languages=f77,c++,objc,ada --disable-win32-registry --disable-shared

  the compiler output (error messages, warnings, etc.):
    bug1.cpp:7: declaration does not declare anything
    bug1.cpp:7: duplicate `const'
    bug1.cpp:7: storage class specified for typename
    bug1.cpp:7: parse error before `=' token
    bug1.cpp: In function `int main()':
    bug1.cpp:18: parse error before `const'

  the complete command line that triggers the bug:
    g++ -Wall -save-temps bug1.cpp

  the preprocessed file (*.i*) that triggers the bug, generated by adding
    -save-temps to the complete compilation command:

    NOTE: this is (to the best of my knowledge) a pre-processor bug, so there
    is an official excuse for not sending the pre-processed version.
>Description:
This is simultaneously an accepts-illegal-rejects-legal
problem.

It seems pretty clear that this is a pre-processor bug.
Indeed, in the pre-processed version,
"static int const CONST = 3;" is converted into
"static int const const = 3;".

IMPORTANT: if the line in "main" that reads
   cout << "foo::CONST = " << foo::CONST << endl;
is removed, then the line "static int const CONST = 3;"
is accepted. Considering that this previous line is
pre-processed as "static int const const = 3;",
this may mean a bug elsewhere in the system:
the combination "const const" is definitely illegal
in this context.
>How-To-Repeat:
  The original file bug1.cpp follows.

  **********************************

  #include <iostream>
  using namespace std;

  class foo {
  public:
    // The following causes an error later.
    static int const CONST = 3;

    // The following compiles, though it probably shouldn't.
    static int CONST c = 4;
  };


  int main()
  {
    // The following doesn't compile, though it should!
    // It complains about "static int const CONST = 3;" above.
    cout << "foo::CONST = " << foo::CONST << endl;
    // If the previous line is removed, then "static int const CONST = 3;"
    // would compile but this would be useless... :(

    cout << "foo::c = " << foo::c << endl;


    return 0;
  }

  // It seems pretty clear that this is a pre-processor bug.
  // Indeed, in the pre-processed version,
  // "static int const CONST = 3;" is converted into
  // "static int const const = 3;".
  //
  // IMPORTANT: if the line in "main" that reads
  //    cout << "foo::CONST = " << foo::CONST << endl;
  // is removed, then the line "static int const CONST = 3;"
  // is accepted. Considering that this previous line is
  // pre-processed as "static int const const = 3;",
  // this may mean a bug elsewhere in the system:
  // the combination "const const" is definitely illegal
  // in this context.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: