gdb: Use std::string_view instead of gdb::string_view

Given that GDB now requires a C++17, replace all uses of
gdb::string_view with std::string_view.

This change has mostly been done automatically:
- gdb::string_view -> std::string_view
- #include "gdbsupport/gdb_string_view.h" -> #include <string_view>

One things which got brought up during review is that gdb::stging_view
does support being built from "nullptr" while std::sting_view does not.
Two places are manually adjusted to account for this difference:
gdb/tui/tui-io.c:tui_getc_1 and
gdbsupport/format.h:format_piece::format_piece.

The above automatic change transformed
"gdb::to_string (const gdb::string_view &)" into
"gdb::to_string (const std::string_view &)".  The various direct users
of this function are now explicitly including
"gdbsupport/gdb_string_view.h".  A later patch will remove the users of
gdb::to_string.

The implementation and tests of gdb::string_view are unchanged, they will
be removed in a following patch.

Change-Id: Ibb806a7e9c79eb16a55c87c6e41ad396fecf0207
Approved-By: Tom Tromey <tom@tromey.com>
Approved-By: Pedro Alves <pedro@palves.net>

5 files changed, 8 insertions, 7 deletions

diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index 58ea541..7c4af3a 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -266,9 +266,9 @@ cooked_index_shard::handle_gnat_encoded_entry (cooked_index_entry *entry,
   std::string canonical = ada_decode (entry->name, false, false);
   if (canonical.empty ())
     return {};
-  std::vector<gdb::string_view> names = split_name (canonical.c_str (),
+  std::vector<std::string_view> names = split_name (canonical.c_str (),
 						    split_style::DOT_STYLE);
-  gdb::string_view tail = names.back ();
+  std::string_view tail = names.back ();
   names.pop_back ();
 
   const cooked_index_entry *parent = nullptr;
@@ -333,7 +333,7 @@ cooked_index_shard::do_finalize ()
   auto eq_entry = [] (const void *a, const void *b) -> int
     {
       const cooked_index_entry *ae = (const cooked_index_entry *) a;
-      const gdb::string_view *sv = (const gdb::string_view *) b;
+      const std::string_view *sv = (const std::string_view *) b;
       return (strlen (ae->canonical) == sv->length ()
 	      && strncasecmp (ae->canonical, sv->data (), sv->length ()) == 0);
     };
diff --git a/gdb/dwarf2/cooked-index.h b/gdb/dwarf2/cooked-index.h
index 5aacb32..5675ea6 100644
--- a/gdb/dwarf2/cooked-index.h
+++ b/gdb/dwarf2/cooked-index.h
@@ -25,7 +25,7 @@
 #include "symtab.h"
 #include "hashtab.h"
 #include "dwarf2/index-common.h"
-#include "gdbsupport/gdb_string_view.h"
+#include <string_view>
 #include "quick-symbol.h"
 #include "gdbsupport/gdb_obstack.h"
 #include "addrmap.h"
diff --git a/gdb/dwarf2/index-common.c b/gdb/dwarf2/index-common.c
index 07330a8..04b04f9 100644
--- a/gdb/dwarf2/index-common.c
+++ b/gdb/dwarf2/index-common.c
@@ -58,7 +58,7 @@ dwarf5_djb_hash (const char *str_)
 /* See dwarf-index-common.h.  */
 
 uint32_t
-dwarf5_djb_hash (gdb::string_view str)
+dwarf5_djb_hash (std::string_view str)
 {
   /* Note: tolower here ignores UTF-8, which isn't fully compliant.
      See http://dwarfstd.org/ShowIssue.php?issue=161027.1.  */
diff --git a/gdb/dwarf2/index-common.h b/gdb/dwarf2/index-common.h
index 23e814a..79d3a59 100644
--- a/gdb/dwarf2/index-common.h
+++ b/gdb/dwarf2/index-common.h
@@ -54,6 +54,6 @@ uint32_t dwarf5_djb_hash (const char *str_);
 
 /* Symbol name hashing function as specified by DWARF-5.  */
 
-uint32_t dwarf5_djb_hash (gdb::string_view str_);
+uint32_t dwarf5_djb_hash (std::string_view str_);
 
 #endif /* DWARF_INDEX_COMMON_H */
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 6d86d28..a16139d 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -96,6 +96,7 @@
 #include "split-name.h"
 #include "gdbsupport/parallel-for.h"
 #include "gdbsupport/thread-pool.h"
+#include "gdbsupport/gdb_string_view.h"
 
 /* When == 1, print basic high level tracing messages.
    When > 1, be more verbose.
@@ -16767,7 +16768,7 @@ cooked_index_functions::expand_symtabs_matching
 
   for (enum language lang : unique_styles)
     {
-      std::vector<gdb::string_view> name_vec
+      std::vector<std::string_view> name_vec
 	= lookup_name_without_params.split_name (lang);
       std::string last_name = gdb::to_string (name_vec.back ());