[Tooling/Inclusion] Add missing placerholder _1 symbols.

[kadircet]

clang/lib/Tooling/Inclusions/Stdlib/StdSpecialSymbolMap.inc

260

libstdc++ actually has _N=29 (don't know why not 30, as it starts from 1 actually :D) you mind listing it all the way till 29?

[hokein]

address comment: add more _N symbol up to _29.

clang/lib/Tooling/Inclusions/Stdlib/StdSpecialSymbolMap.inc

 
 // cppreference symbol index page was missing these symbols.
 // Remove them when the cppreference offline archive catches up.
 SYMBOL(index_sequence, std::, <utility>)
 SYMBOL(index_sequence_for, std::, <utility>)
 SYMBOL(make_index_sequence, std::, <utility>)
 SYMBOL(make_integer_sequence, std::, <utility>)
 
+// The std::placeholder symbols (_1, ..., _N) are listed in the cppreference
+// placeholder.html, but the index only contains a single entry with "_1, _2, ..., _N"
+// text, which are not handled by the script.
+// N is an implementation-defined number (10 for libc++; 29 for libstdc++).
+SYMBOL(_1, std::placeholders::, <functional>)
+SYMBOL(_2, std::placeholders::, <functional>)
+SYMBOL(_3, std::placeholders::, <functional>)
+SYMBOL(_4, std::placeholders::, <functional>)
+SYMBOL(_5, std::placeholders::, <functional>)
+SYMBOL(_6, std::placeholders::, <functional>)
+SYMBOL(_7, std::placeholders::, <functional>)
+SYMBOL(_8, std::placeholders::, <functional>)
+SYMBOL(_9, std::placeholders::, <functional>)
+SYMBOL(_10, std::placeholders::, <functional>)
+SYMBOL(_11, std::placeholders::, <functional>)
+SYMBOL(_12, std::placeholders::, <functional>)
+SYMBOL(_13, std::placeholders::, <functional>)
+SYMBOL(_14, std::placeholders::, <functional>)
+SYMBOL(_15, std::placeholders::, <functional>)
+SYMBOL(_16, std::placeholders::, <functional>)
+SYMBOL(_17, std::placeholders::, <functional>)
+SYMBOL(_18, std::placeholders::, <functional>)
+SYMBOL(_19, std::placeholders::, <functional>)
+SYMBOL(_20, std::placeholders::, <functional>)
+SYMBOL(_21, std::placeholders::, <functional>)
+SYMBOL(_22, std::placeholders::, <functional>)
+SYMBOL(_23, std::placeholders::, <functional>)
+SYMBOL(_24, std::placeholders::, <functional>)
+SYMBOL(_25, std::placeholders::, <functional>)
+SYMBOL(_26, std::placeholders::, <functional>)
+SYMBOL(_27, std::placeholders::, <functional>)
+SYMBOL(_28, std::placeholders::, <functional>)
+SYMBOL(_29, std::placeholders::, <functional>)
+
 // Macros
 SYMBOL(NULL, None, <cstddef>)
 SYMBOL(NULL, None, <stddef.h>)
 SYMBOL(NULL, None, <cstdlib>)
 SYMBOL(NULL, None, <stdlib.h>)
 SYMBOL(NULL, None, <cstring>)
 SYMBOL(NULL, None, <string.h>)
 SYMBOL(NULL, None, <cwchar>)
 SYMBOL(NULL, None, <wchar.h>)
 SYMBOL(NULL, None, <ctime>)
 SYMBOL(NULL, None, <time.h>)
 SYMBOL(NULL, None, <clocale>)
 SYMBOL(NULL, None, <locale.h>)
 SYMBOL(NULL, None, <cstdio>)
 SYMBOL(NULL, None, <stdio.h>)

clang/tools/include-mapping/gen_std.py

if args.symbols == 'cpp':
     page_root = os.path.join(args.cppreference, "en", "cpp")
     symbol_index_root = os.path.join(page_root, "symbol_index")
     parse_pages =  [
       (page_root, "symbol_index.html", "std::"),
       # std sub-namespace symbols have separated pages.
       # We don't index std literal operators (e.g.
       # std::literals::chrono_literals::operator""d), these symbols can't be
       # accessed by std::<symbol_name>.
-      # FIXME: index std::placeholders symbols, placeholders.html page is
-      # different (which contains one entry for _1, _2, ..., _N), we need special
-      # handling.
+      #
+      # std::placeholders symbols are handled manually in StdSpecialSymbolMap.inc
       (symbol_index_root, "chrono.html", "std::chrono::"),
       (symbol_index_root, "filesystem.html", "std::filesystem::"),
       (symbol_index_root, "pmr.html", "std::pmr::"),
       (symbol_index_root, "regex_constants.html", "std::regex_constants::"),
       (symbol_index_root, "this_thread.html", "std::this_thread::"),
       # Zombie symbols that were available from the Standard Library, but are
       # removed in the following standards.
       (symbol_index_root, "zombie_names.html", "std::"),