Re: [PATCH] libstdc++, configure: Fix GLIBCXX_ZONEINFO_DIR configuration macro.

[Jonathan Wakely <jwakely@redhat.com>]

On 14/01/23 18:24 +0000, Jonathan Wakely wrote:
>On 23/12/22 17:06 +0000, Iain Sandoe wrote:
>>This is a patch for comment on the approach - tested on x86_64-darwi21
>>thoughts?
>>Iain
>>
>>--- 8< ---
>>
>>Testing on Darwin revealed that the GLIBCXX_ZONEINFO_DIR was not doing quite
>>the right thing (we ended up with ${withval} in the config.h file).
>>
>>This patch proposes revising the behaviour of the configure flag thus:
>>
>>--with-libstdcxx-zoneinfo-dir=
>>unspecified : Set _GLIBCXX_ZONEINFO_DIR to a default suitable for $host
>>        yes : Set _GLIBCXX_ZONEINFO_DIR to a default suitable for $host
>>        no  : Do not set _GLIBCXX_ZONEINFO_DIR
>>/some/path  : set _GLIBCXX_ZONEINFO_DIR = "/some/path"
>
>Here's what I've pushed to trunk now, after discussion with Iain.

This is a small follow-up to elide most of the code in
src/c++20/tzdb.cc when the library is configured with
--with-libstdcxx-zoneinfo=no

Tested x86_64-linux and powerpc64le-linux. Pushed to trunk.

-- >8 --

commit c47dcb95666ce0b48f0ff09aa99483fd12df8714
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sat Jan 14 13:39:48 2023

     libstdc++: Disable unwanted code for --with-libstdcxx-zoneinfo=no
     
     This allows most of the tzdb functionality to be disabled by
     configuring with --with-libstdcxx-zoneinfo=no. This might be desirable
     for small targets that don't need the time zone support.
     
     libstdc++-v3/ChangeLog:
     
             * src/c++20/tzdb.cc (TZDB_DISABLED): Disable all code for
             loading tzdb.
             * testsuite/std/time/tzdb/leap_seconds.cc: Require tzdb
             effective target.
             * testsuite/std/time/tzdb_list/1.cc: Likewise.

diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index 94fb0436091..a37859dffdb 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -82,6 +82,14 @@ namespace __gnu_cxx
  #endif
  }
  
+#if ! defined _GLIBCXX_ZONEINFO_DIR && ! defined _GLIBCXX_STATIC_TZDATA
+# define TZDB_DISABLED
+  [[noreturn]] void __throw_disabled()
+  {
+    std::__throw_runtime_error("tzdb: support for loading tzdata is disabled");
+  }
+#endif
+
  namespace std::chrono
  {
    namespace
@@ -105,7 +113,9 @@ namespace std::chrono
    {
      shared_ptr<_Node> next;
      tzdb db;
+#ifndef TZDB_DISABLED
      vector<Rule> rules;
+#endif
  
      // The following static members are here because making them members
      // of this type gives them access to the private members of time_zone
@@ -175,6 +185,7 @@ namespace std::chrono
    // assume that setting failbit will throw an exception, so individual
    // input operations are not always checked for success.
  
+#ifndef TZDB_DISABLED
    namespace
    {
      // Used for reading a possibly-quoted string from a stream.
@@ -582,6 +593,7 @@ namespace std::chrono
  #endif
      };
    } // namespace
+#endif // TZDB_DISABLED
  
    // Private constructor used by reload_tzdb() to create time_zone objects.
    time_zone::time_zone(unique_ptr<_Impl> __p) : _M_impl(std::move(__p)) { }
@@ -591,6 +603,7 @@ namespace std::chrono
    // The opaque pimpl class stored in a time_zone object.
    struct time_zone::_Impl
    {
+#ifndef TZDB_DISABLED
      explicit
      _Impl(weak_ptr<tzdb_list::_Node> node) : node(std::move(node)) { }
  
@@ -677,11 +690,19 @@ namespace std::chrono
  	  }
  	}
        };
-#endif
+#endif // __GTHREADS && __cpp_lib_atomic_wait
  
      RulesCounter<atomic_signed_lock_free> rules_counter;
+#else // TZDB_DISABLED
+    _Impl(weak_ptr<tzdb_list::_Node>) { }
+    struct {
+      sys_info info;
+      void push_back(sys_info i) { info = std::move(i); }
+    } infos;
+#endif // TZDB_DISABLED
    };
  
+#ifndef TZDB_DISABLED
    namespace
    {
      bool
@@ -731,11 +752,13 @@ namespace std::chrono
  	select_std_or_dst_abbrev(info.abbrev, info.save);
      }
    }
+#endif // TZDB_DISABLED
  
    // Implementation of std::chrono::time_zone::get_info(const sys_time<D>&)
    sys_info
    time_zone::_M_get_sys_info(sys_seconds tp) const
    {
+#ifndef TZDB_DISABLED
      // This gives us access to the node->rules vector, but also ensures
      // that the tzdb node won't get erased while we're still using it.
      const auto node = _M_impl->node.lock();
@@ -934,17 +957,20 @@ namespace std::chrono
  	// Decrement count of rule-based infos (might also release lock).
  	_M_impl->rules_counter.decrement();
        }
-
      return info;
+#else
+    return _M_impl->infos.info;
+#endif // TZDB_DISABLED
    }
  
    // Implementation of std::chrono::time_zone::get_info(const local_time<D>&)
    local_info
    time_zone::_M_get_local_info(local_seconds tp) const
    {
+    local_info info{};
+#ifndef TZDB_DISABLED
      const auto node = _M_impl->node.lock();
  
-    local_info info{};
      // Get sys_info assuming no offset between local time and UTC:
      info.first = _M_get_sys_info(sys_seconds(tp.time_since_epoch()));
  
@@ -1007,9 +1033,13 @@ namespace std::chrono
  	  }
  	// else tp is a unique local time, info.first is the correct sys_info.
        }
+#else
+    info.first = _M_impl->infos.info;
+#endif // TZDB_DISABLED
      return info;
    }
  
+#ifndef TZDB_DISABLED
    namespace
    {
      // If a zoneinfo directory is defined (either when the library was built,
@@ -1088,14 +1118,13 @@ namespace std::chrono
        bool using_static_data() const { return this->rdbuf() == &sb; }
      };
    }
+#endif // TZDB_DISABLED
  
    // Return leap_second values, and a bool indicating whether the values are
    // current (true), or potentially out of date (false).
    pair<vector<leap_second>, bool>
    tzdb_list::_Node::_S_read_leap_seconds()
    {
-    const string filename = zoneinfo_file(leaps_file);
-
      // This list is valid until at least 2023-06-28 00:00:00 UTC.
      auto expires = sys_days{2023y/6/28};
      vector<leap_second> leaps
@@ -1137,10 +1166,10 @@ namespace std::chrono
        return {std::move(leaps), true};
  #endif
  
-    auto exp_year = year_month_day(expires).year();
-
-    if (ifstream ls{filename})
+#ifndef TZDB_DISABLED
+    if (ifstream ls{zoneinfo_file(leaps_file)})
        {
+	auto exp_year = year_month_day(expires).year();
  	std::string s, w;
  	s.reserve(80); // Avoid later reallocations.
  	while (std::getline(ls, s))
@@ -1183,10 +1212,11 @@ namespace std::chrono
  	  }
  	return {std::move(leaps), true};
        }
-    else
-      return {std::move(leaps), false};
+#endif
+    return {std::move(leaps), false};
    }
  
+#ifndef TZDB_DISABLED
    namespace
    {
      // Read the version number from a tzdata.zi file.
@@ -1213,12 +1243,17 @@ namespace std::chrono
        __throw_runtime_error("tzdb: no version found in tzdata.zi");
      }
    }
+#endif
  
    // Definition of std::chrono::remote_version()
    string remote_version()
    {
+#ifndef TZDB_DISABLED
      tzdata_stream zif;
      return remote_version(zif);
+#else
+    __throw_disabled();
+#endif
    }
  
    // Used by chrono::reload_tzdb() to add a new node to the front of the list.
@@ -1255,11 +1290,13 @@ namespace std::chrono
    const tzdb&
    tzdb_list::_Node::_S_init_tzdb()
    {
+#ifndef TZDB_DISABLED
      __try
        {
  	return reload_tzdb();
        }
      __catch (const std::exception&)
+#endif
        {
  	auto [leaps, ok] = _S_read_leap_seconds();
  
@@ -1349,6 +1386,7 @@ namespace std::chrono
    const tzdb&
    reload_tzdb()
    {
+#ifndef TZDB_DISABLED
      using Node = tzdb_list::_Node;
  
      tzdata_stream zif;
@@ -1458,6 +1496,9 @@ namespace std::chrono
      shared_ptr<Node> head;
  #endif
      return Node::_S_replace_head(std::move(head), std::move(node));
+#else
+    __throw_disabled();
+#endif // TZDB_DISABLED
    }
  
    // Any call to tzdb_list::front() or tzdb_list::begin() must follow
@@ -1641,6 +1682,7 @@ namespace std::chrono
      return get_tzdb_list().begin()->current_zone();
    }
  
+#ifndef TZDB_DISABLED
    namespace
    {
      istream& operator>>(istream& in, abbrev_month& am)
@@ -1933,5 +1975,5 @@ namespace std::chrono
        return in;
      }
    } // namespace
-
+#endif // TZDB_DISABLED
  } // namespace std::chrono
diff --git a/libstdc++-v3/testsuite/std/time/tzdb/leap_seconds.cc b/libstdc++-v3/testsuite/std/time/tzdb/leap_seconds.cc
index 2b289436583..d27038225c8 100644
--- a/libstdc++-v3/testsuite/std/time/tzdb/leap_seconds.cc
+++ b/libstdc++-v3/testsuite/std/time/tzdb/leap_seconds.cc
@@ -1,5 +1,6 @@
  // { dg-options "-std=gnu++20" }
  // { dg-do run { target c++20 } }
+// { dg-require-effective-target tzdb }
  // { dg-require-effective-target cxx11_abi }
  // { dg-xfail-run-if "no weak override on AIX" { powerpc-ibm-aix* } }
  
diff --git a/libstdc++-v3/testsuite/std/time/tzdb_list/1.cc b/libstdc++-v3/testsuite/std/time/tzdb_list/1.cc
index 4cbd656efbd..2b121ff219d 100644
--- a/libstdc++-v3/testsuite/std/time/tzdb_list/1.cc
+++ b/libstdc++-v3/testsuite/std/time/tzdb_list/1.cc
@@ -1,5 +1,6 @@
  // { dg-options "-std=gnu++20" }
  // { dg-do run { target c++20 } }
+// { dg-require-effective-target tzdb }
  // { dg-require-effective-target cxx11_abi }
  // { dg-xfail-run-if "no weak override on AIX" { powerpc-ibm-aix* } }