gdb/fortran: add support for parsing array strides in expressions

With this commit GDB now understands the syntax of Fortran array
strides, a user can type an expression including an array stride, but
they will only get an error informing them that array strides are not
supported.

This alone is an improvement on what we had before in GDB, better to
give the user a helpful message that a particular feature is not
supported than to just claim a syntax error.

Before:

  (gdb) p array (1:10:2, 2:10:2)
  A syntax error in expression, near `:2, 2:10:2)'.

Now:

  (gdb) p array (1:10:2, 2:10:2)
  Fortran array strides are not currently supported

Later commits will allow GDB to handle array strides correctly.

gdb/ChangeLog:

	* expprint.c (dump_subexp_body_standard): Print RANGE_HAS_STRIDE.
	* expression.h (enum range_type): Add RANGE_HAS_STRIDE.
	* f-exp.y (arglist): Allow for a series of subranges.
	(subrange): Add cases for subranges with strides.
	* f-lang.c (value_f90_subarray): Catch use of array strides and
	throw an error.
	* parse.c (operator_length_standard): Handle RANGE_HAS_STRIDE.

gdb/testsuite/ChangeLog:

	* gdb.fortran/array-slices.exp: Add a new test.

1 files changed, 2 insertions, 0 deletions

diff --git a/gdb/parse.c b/gdb/parse.c
index 4a15de8..359ab62 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -924,6 +924,8 @@ operator_length_standard (const struct expression *expr, int endpos,
       /* Assume the range has 2 arguments (low bound and high bound), then
 	 reduce the argument count if any bounds are set to default.  */
       args = 2;
+      if (range_flag & RANGE_HAS_STRIDE)
+	++args;
       if (range_flag & RANGE_LOW_BOUND_DEFAULT)
 	--args;
       if (range_flag & RANGE_HIGH_BOUND_DEFAULT)