Teach gdb::option about string options

A following patch will make the "pipe" command use the gdb::option
framework for option processing.  However, "pipe"'s only option today
is a string option, "-d DELIM", and gdb::option does not support
string options yet.

This commit adds support for string options, mapped to var_string.
For now, a string is parsed up until the first whitespace.  I imagine
that we'll need to add support for quoting so that we could do:

 (gdb) cmd -option 'some -string'

without gdb confusing the "-string" for an option.

This doesn't seem important for pipe, so I'm leaving it for another
day.

One thing I'm not happy with, is that the string data is managed as a
raw malloc-allocated char *, which means that we need to xfree it
manually.  This is because var_string settings work that way too.
Although with var_string settings we're leaking the strings at gdb
exit, that was never really a problem.  For options though, leaking is
undesirable.

I think we should tackle that for both settings and options at the
same time, so for now I'm just managing the malloced data manually.
It's a bit ugly in option_def_and_value, but at least that's hidden
from view.

For testing, this adds a new "-string" option to "maint
test-settings", and then tweaks gdb.base/options.exp to exercise it.

gdb/ChangeLog:
2019-07-03  Pedro Alves  <palves@redhat.com>

	* cli/cli-option.c (union option_value) <string>: New field.
	(struct option_def_and_value): Add ctor, move ctor, dtor and
	use DISABLE_COPY_AND_ASSIGN.
	(option_def_and_value::clear_value): New.
	(parse_option, save_option_value_in_ctx, get_val_type_str)
	(add_setshow_cmds_for_options): Handle var_string.
	* cli-option.h (union option_def::var_address) <string>: New
	field.
	(struct string_option_def): New.
	* maint-test-options.c (struct test_options_opts): Add default
	ctor and use DISABLE_COPY_AND_ASSIGN.
	<string_opt>: New field.
	(test_options_opts::~test_options_opts): New.
	(test_options_opts::dump): Also dump "-string".
	(test_options_option_defs): Install "string.

gdb/testsuite/ChangeLog:
2019-07-03  Pedro Alves  <palves@redhat.com>

	* gdb.base/options.exp (expect_none, expect_flag, expect_bool)
	(expect_integer): Adjust to expect "-string".
	(expect_string): New.
	(all_options): Expect "-string".
	(test-flag, test-boolean): Adjust to expect "-string".
	(test-string): New proc.
	(top level): Call it.

1 files changed, 24 insertions, 3 deletions

diff --git a/gdb/maint-test-options.c b/gdb/maint-test-options.c
index 7e7ef6e7992..4caa865ae43 100644
--- a/gdb/maint-test-options.c
+++ b/gdb/maint-test-options.c
@@ -58,10 +58,10 @@
    readline, for proper testing of TAB completion.
 
    These maintenance commands support options of all the different
-   available kinds of commands (boolean, enum, flag, uinteger):
+   available kinds of commands (boolean, enum, flag, string, uinteger):
 
     (gdb) maint test-options require-delimiter -[TAB]
-    -bool      -enum      -flag      -uinteger   -xx1       -xx2
+    -bool      -enum      -flag      -string     -uinteger   -xx1       -xx2
 
     (gdb) maint test-options require-delimiter -bool o[TAB]
     off  on
@@ -133,6 +133,16 @@ struct test_options_opts
   const char *enum_opt = test_options_enum_values_xxx;
   unsigned int uint_opt = 0;
   int zuint_unl_opt = 0;
+  char *string_opt = nullptr;
+
+  test_options_opts () = default;
+
+  DISABLE_COPY_AND_ASSIGN (test_options_opts);
+
+  ~test_options_opts ()
+  {
+    xfree (string_opt);
+  }
 
   /* Dump the options to FILE.  ARGS is the remainder unprocessed
      arguments.  */
@@ -140,7 +150,7 @@ struct test_options_opts
   {
     fprintf_unfiltered (file,
 			_("-flag %d -xx1 %d -xx2 %d -bool %d "
-			  "-enum %s -uint %s -zuint-unl %s -- %s\n"),
+			  "-enum %s -uint %s -zuint-unl %s -string '%s' -- %s\n"),
 			flag_opt,
 			xx1_opt,
 			xx2_opt,
@@ -152,6 +162,9 @@ struct test_options_opts
 			(zuint_unl_opt == -1
 			 ? "unlimited"
 			 : plongest (zuint_unl_opt)),
+			(string_opt != nullptr
+			 ? string_opt
+			 : ""),
 			args);
   }
 };
@@ -216,6 +229,14 @@ static const gdb::option::option_def test_options_option_defs[] = {
     nullptr, /* show_doc */
     nullptr, /* help_doc */
   },
+
+  /* A string option.  */
+  gdb::option::string_option_def<test_options_opts> {
+    "string",
+    [] (test_options_opts *opts) { return &opts->string_opt; },
+    nullptr, /* show_cmd_cb */
+    N_("A string option."),
+  },
 };
 
 /* Create an option_def_group for the test_options_opts options, with