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.

8 files changed, 84 insertions, 1 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d67de7c05a7..bf93e1b8a26 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,15 @@
 2020-10-22  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* 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.
+
+2020-10-22  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* expprint.c (print_subexp_standard): Change enum range_type to
 	range_flag and rename variables to match.
 	(dump_subexp_body_standard): Likewise.
diff --git a/gdb/expprint.c b/gdb/expprint.c
index 2dee2bb1932..a14eeb00f19 100644
--- a/gdb/expprint.c
+++ b/gdb/expprint.c
@@ -1120,12 +1120,16 @@ dump_subexp_body_standard (struct expression *exp,
 	fputs_filtered ("..", stream);
 	if (!(range_flag & RANGE_HIGH_BOUND_DEFAULT))
 	  fputs_filtered ("EXP", stream);
+	if (range_flag & RANGE_HAS_STRIDE)
+	  fputs_filtered (":EXP", stream);
 	fputs_filtered ("'", stream);
 
 	if (!(range_flag & RANGE_LOW_BOUND_DEFAULT))
 	  elt = dump_subexp (exp, stream, elt);
 	if (!(range_flag & RANGE_HIGH_BOUND_DEFAULT))
 	  elt = dump_subexp (exp, stream, elt);
+	if (range_flag & RANGE_HAS_STRIDE)
+	  elt = dump_subexp (exp, stream, elt);
       }
       break;
 
diff --git a/gdb/expression.h b/gdb/expression.h
index fd483e5f277..8de712310ec 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -199,6 +199,9 @@ enum range_flag : unsigned
 
   /* The high bound of this range is exclusive.  */
   RANGE_HIGH_BOUND_EXCLUSIVE = 1 << 2,
+
+  /* The range has a stride.  */
+  RANGE_HAS_STRIDE = 1 << 3,
 };
 
 DEF_ENUM_FLAGS_TYPE (enum range_flag, range_flags);
diff --git a/gdb/f-exp.y b/gdb/f-exp.y
index a3314082d90..eaa72142431 100644
--- a/gdb/f-exp.y
+++ b/gdb/f-exp.y
@@ -284,6 +284,10 @@ arglist	:	arglist ',' exp   %prec ABOVE_COMMA
 			{ pstate->arglist_len++; }
 	;
 
+arglist	:	arglist ',' subrange   %prec ABOVE_COMMA
+			{ pstate->arglist_len++; }
+	;
+
 /* There are four sorts of subrange types in F90.  */
 
 subrange:	exp ':' exp	%prec ABOVE_COMMA
@@ -314,6 +318,38 @@ subrange:	':'	%prec ABOVE_COMMA
 			  write_exp_elt_opcode (pstate, OP_RANGE); }
 	;
 
+/* And each of the four subrange types can also have a stride.  */
+subrange:	exp ':' exp ':' exp	%prec ABOVE_COMMA
+			{ write_exp_elt_opcode (pstate, OP_RANGE);
+			  write_exp_elt_longcst (pstate, RANGE_HAS_STRIDE);
+			  write_exp_elt_opcode (pstate, OP_RANGE); }
+	;
+
+subrange:	exp ':' ':' exp	%prec ABOVE_COMMA
+			{ write_exp_elt_opcode (pstate, OP_RANGE);
+			  write_exp_elt_longcst (pstate,
+						 (RANGE_HIGH_BOUND_DEFAULT
+						  | RANGE_HAS_STRIDE));
+			  write_exp_elt_opcode (pstate, OP_RANGE); }
+	;
+
+subrange:	':' exp ':' exp	%prec ABOVE_COMMA
+			{ write_exp_elt_opcode (pstate, OP_RANGE);
+			  write_exp_elt_longcst (pstate,
+						 (RANGE_LOW_BOUND_DEFAULT
+						  | RANGE_HAS_STRIDE));
+			  write_exp_elt_opcode (pstate, OP_RANGE); }
+	;
+
+subrange:	':' ':' exp	%prec ABOVE_COMMA
+			{ write_exp_elt_opcode (pstate, OP_RANGE);
+			  write_exp_elt_longcst (pstate,
+						 (RANGE_LOW_BOUND_DEFAULT
+						  | RANGE_HIGH_BOUND_DEFAULT
+						  | RANGE_HAS_STRIDE));
+			  write_exp_elt_opcode (pstate, OP_RANGE); }
+	;
+
 complexnum:     exp ',' exp 
                 	{ }                          
         ;
diff --git a/gdb/f-lang.c b/gdb/f-lang.c
index 37d05b27653..f7c54b462a4 100644
--- a/gdb/f-lang.c
+++ b/gdb/f-lang.c
@@ -124,7 +124,7 @@ value_f90_subarray (struct value *array,
 		    struct expression *exp, int *pos, enum noside noside)
 {
   int pc = (*pos) + 1;
-  LONGEST low_bound, high_bound;
+  LONGEST low_bound, high_bound, stride;
   struct type *range = check_typedef (value_type (array)->index_type ());
   enum range_flag range_flag
     = (enum range_flag) longest_to_int (exp->elts[pc].longconst);
@@ -141,6 +141,14 @@ value_f90_subarray (struct value *array,
   else
     high_bound = value_as_long (evaluate_subexp (nullptr, exp, pos, noside));
 
+  if (range_flag & RANGE_HAS_STRIDE)
+    stride = value_as_long (evaluate_subexp (nullptr, exp, pos, noside));
+  else
+    stride = 1;
+
+  if (stride != 1)
+    error (_("Fortran array strides are not currently supported"));
+
   return value_slice (array, low_bound, high_bound - low_bound + 1);
 }
 
diff --git a/gdb/parse.c b/gdb/parse.c
index 4a15de8a499..359ab6211aa 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)
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 4061d1789cc..19b423beb3c 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-10-22  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.fortran/array-slices.exp: Add a new test.
+
 2020-10-21  Gary Benson <gbenson@redhat.com>
 
 	* gdb.mi/mi-fullname-deleted.exp: Fix substituted
diff --git a/gdb/testsuite/gdb.fortran/array-slices.exp b/gdb/testsuite/gdb.fortran/array-slices.exp
index 31f95a3668d..aa6bc6327eb 100644
--- a/gdb/testsuite/gdb.fortran/array-slices.exp
+++ b/gdb/testsuite/gdb.fortran/array-slices.exp
@@ -69,3 +69,19 @@ foreach result $array_contents msg $message_strings {
 }
 
 gdb_continue_to_breakpoint "continue to Final Breakpoint"
+
+# Next test that asking for an array with stride at the CLI gives an
+# error.
+clean_restart ${testfile}
+
+if ![fortran_runto_main] then {
+    perror "couldn't run to main"
+    continue
+}
+
+gdb_breakpoint "show"
+gdb_continue_to_breakpoint "show"
+gdb_test "up" ".*"
+gdb_test "p array (1:10:2, 1:10:2)" \
+    "Fortran array strides are not currently supported" \
+    "using array stride gives an error"