[RFA patch, Fortran] PR60144 - Misleading error message when missing "then" after "if" and "else if"

[Dominique d'Humières]

With the proposed patch

    2 |     if (.TRUE.)      
      |                      1
Error: Cannot assign to a named constant at (1)
    3 |     else if (.FALSE.) 
      |           1
Error: Unexpected junk after ELSE statement at (1)

is changed to

    2 |     if (.TRUE.)      
      |                      1
Error: Syntax error in IF-clause after (1)
    3 |     else if (.FALSE.) 
      |                     1
Error: Missing THEN in ELSE IF statement after (1)

The first change is done by removing the block

/* The gfc_match_assignment() above may have returned a MATCH_NO
…
   return MATCH_ERROR;
}

This block has been introduced at revision r116570 to handle assignment to a named constant as in the test
simpleif_2.f90, but this is now handled elsewhere.

The second change is done by some more parsing of the ELSE IF statement.

While at these changes, I have also made the error

    3 |     if (.FALSE. then c="!" 
      |        1
Error: Missing ')' in statement at or before (1)

to be less surprising

    3 |     if (.FALSE. then c="!" 
      |                           1
Error: Missing ')' in statement at or before (1)

Also

    7 |     if a=b                 ! 
      |    1
Error: Unclassifiable statement at (1)

changed to

    7 |     if a=b                 ! 
      |       1
Error: Missing '(' in IF-expression at (1)

which avoids the error to be deleted if it appears after other ones.

Bootstrapped and tested on darwin. Is it OK for trunk?

TIA

Dominique

2019-03-17  Dominique d'Humieres  <dominiq@gcc.gnu.org>

	PR fortran/60144
	* match.c (gfc_match_parens): Change the location for missing ')'.
	(gfc_match_if): Detect a missing '('. Remove the spurious named
	constant error. Change the wording of some errors.
	(gfc_match_else): Change the wording of an error.
	(gfc_match_elseif): Detect a missing '('. Improve the matching
	process to get a better syntax analysis.

2019-03-17  Dominique d'Humieres  <dominiq@gcc.gnu.org>

	PR fortran/60144
	* gfortran.dg/block_name_2.f90: Adjust dg-error.
	* gfortran.dg/dec_type_print_3.f90.f90: Likewise
	* gfortran.dg/pr60144.f90: New test. 

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