gdb/fortran/testsuite: print values and types of string variables

While looking through the Fortran tests, I couldn't find a test of GDB
printing the value and type of a Fortran string defined using the
'character*SIZE' notation.

This works fine in GDB right now, but I thought it wouldn't hurt to
have a test for this, so this commit adds such a test.

The test also includes printing a string that includes some embedded
special characters: \n \r \t \000 - that's right, as Fortran strings
are stored as an address and length, it is fine to include an embedded
null, so this test includes an example of that.

Standard Fortran doesn't support backslash escape sequences within
strings, the special characters must be generated using the `achar`
function.  However, when GDB prints the strings we currently print
using the standard C like backslash sequences.

I'm not currently proposing to change that behaviour, the backslash
sequences are more compact than the standard Fortran way of doing
things, and are so widely used that I suspect most Fortran programmers
will understand them.

gdb/testsuite/gdb.fortran/string-types.exp

@@ -0,0 +1,70 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test print the value, and type, of Fortran string variables declared in
+# different ways in the test program.
+
+standard_testfile .f90
+load_lib fortran.exp
+
+if {[skip_fortran_tests]} { return -1 }
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile \
+	 {debug f90 quiet}]} {
+    return -1
+}
+
+if { ![fortran_runto_main] } {
+    perror "Couldn't run to main"
+    return
+}
+
+gdb_breakpoint [gdb_get_line_number "First breakpoint"]
+gdb_breakpoint [gdb_get_line_number "Second breakpoint"]
+gdb_breakpoint [gdb_get_line_number "Third breakpoint"]
+
+with_test_prefix "first breakpoint" {
+    # Continue to the first breakpoint.
+    gdb_continue_to_breakpoint "continue"
+    gdb_test "print s" " = 'foo'"
+    gdb_test "ptype s" "type = character\\*3"
+}
+
+with_test_prefix "second breakpoint" {
+    # Continue to the second breakpoint.
+    gdb_continue_to_breakpoint "continue"
+    gdb_test "print s" " = 'foo'"
+    gdb_test "ptype s" "type = character\\*3"
+}
+
+with_test_prefix "third breakpoint, first time" {
+    # Continue to the third breakpoint.
+    gdb_continue_to_breakpoint "continue"
+    gdb_test "print s" " = 'foo'"
+    gdb_test "ptype s" "type = character \\(3\\)"
+}
+
+with_test_prefix "third breakpoint, second time" {
+    # Continue to the third breakpoint again.  The string we print
+    # this time includes some embedded special characters (newline,
+    # tab, carriage-return, and an embedded null byte).  Currently GDB
+    # prints these as C style backslash sequences, which isn't valid
+    # Fortran code, but is more compact than the Fortran way of doing
+    # it (see the test source for details), and is likely understood
+    # by most users, so seems good enough.
+    gdb_continue_to_breakpoint "continue"
+    gdb_test "print s" " = 'foo\\\\n\\\\t\\\\r\\\\000bar'"
+    gdb_test "ptype s" "type = character \\(10\\)"
+}

gdb/testsuite/gdb.fortran/string-types.f90

@@ -0,0 +1,37 @@
+! Copyright 2022 Free Software Foundation, Inc.
+!
+! This program is free software; you can redistribute it and/or modify
+! it under the terms of the GNU General Public License as published by
+! the Free Software Foundation; either version 3 of the License, or
+! (at your option) any later version.
+!
+! This program is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License
+! along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+subroutine fixed_size_string_v1(s)
+  character*3 s
+  print *, ""	! First breakpoint.
+end subroutine fixed_size_string_v1
+
+subroutine fixed_size_string_v2(s)
+  character(3) s
+  print *, ""	! Second breakpoint.
+end subroutine fixed_size_string_v2
+
+subroutine variable_size_string(s)
+  character*(*) s
+  print *, ""	! Third breakpoint.
+end subroutine variable_size_string
+
+program test
+  call fixed_size_string_v1('foo')
+  call fixed_size_string_v2('foo')
+  call variable_size_string('foo')
+  call variable_size_string('foo' // achar(10) // achar(9) // achar(13) // &
+			    achar(0) // 'bar')
+end program test