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authorBoris Kolpackov <boris@codesynthesis.com>2021-04-04 13:11:56 +0200
committerBoris Kolpackov <boris@codesynthesis.com>2021-04-04 13:11:56 +0200
commit5e51d523e71231cb190e9ed981962df527f4ee7e (patch)
tree1ca26842d0629d23feb10c498364758a90f2dd68
parentb3bc26dc284cf73e97b88c9979d49368d07e686c (diff)
Add base functionality for hermetic build configurationshermetic
-rw-r--r--libbuild2/config/functions.cxx7
-rw-r--r--libbuild2/config/init.cxx206
-rw-r--r--libbuild2/config/module.hxx70
-rw-r--r--libbuild2/config/operation.cxx140
-rw-r--r--libbuild2/config/operation.hxx7
-rw-r--r--libbuild2/variable.cxx8
-rw-r--r--libbuild2/variable.hxx19
7 files changed, 345 insertions, 112 deletions
diff --git a/libbuild2/config/functions.cxx b/libbuild2/config/functions.cxx
index 5e85238..398512c 100644
--- a/libbuild2/config/functions.cxx
+++ b/libbuild2/config/functions.cxx
@@ -7,6 +7,7 @@
#include <libbuild2/function.hxx>
#include <libbuild2/variable.hxx>
+#include <libbuild2/config/module.hxx>
#include <libbuild2/config/operation.hxx>
using namespace std;
@@ -39,6 +40,11 @@ namespace build2
if (s == nullptr)
fail << "config.save() called out of project" << endf;
+ module* mod (s->find_module<module> (module::name));
+
+ if (mod == nullptr)
+ fail << "config.save() called without config module";
+
ostringstream os;
// Empty project set should is ok as long as inherit is false.
@@ -47,6 +53,7 @@ namespace build2
save_config (*s,
os, path_name ("config.save()"),
false /* inherit */,
+ *mod,
ps);
return os.str ();
diff --git a/libbuild2/config/init.cxx b/libbuild2/config/init.cxx
index 1e6b36b..950579a 100644
--- a/libbuild2/config/init.cxx
+++ b/libbuild2/config/init.cxx
@@ -5,7 +5,6 @@
#include <sstream>
#include <cstdlib> // getenv()
-#include <cstring> // strncmp()
#include <libbuild2/file.hxx>
#include <libbuild2/rule.hxx>
@@ -30,24 +29,6 @@ namespace build2
void
functions (function_map&); // functions.cxx
- // Compare environment variable names. Note that on Windows they are
- // case-insensitive.
- //
- static inline bool
- compare_env (const string& x, size_t xn, const string& y, size_t yn)
- {
- if (xn == string::npos) xn = x.size ();
- if (yn == string::npos) yn = y.size ();
-
- return xn == yn &&
-#ifdef _WIN32
- icasecmp (x.c_str (), y.c_str (), xn) == 0
-#else
- strncmp (x.c_str (), y.c_str (), xn) == 0
-#endif
- ;
- }
-
// Custom save function for config.config.environment.
//
// It tries to optimize the storage in subprojects by appending the
@@ -82,7 +63,8 @@ namespace build2
if (find_if (ds.rbegin (), i,
[&v, p] (const string& v1)
{
- return compare_env (v, p, v1, v1.find ('='));
+ return saved_environment::compare (
+ v, v1, p, v1.find ('='));
}) != i)
continue;
@@ -91,7 +73,8 @@ namespace build2
auto j (find_if (bs.rbegin (), bs.rend (),
[&v, p] (const string& v1)
{
- return compare_env (v, p, v1, v1.find ('='));
+ return saved_environment::compare (
+ v, v1, p, v1.find ('='));
}));
if (j == bs.rend () || *j != v)
@@ -130,7 +113,7 @@ namespace build2
// as a command line override.
//
// Note: must be entered during bootstrap since we need it in
- // configure_execute().
+ // configure_execute() even for the forward case.
//
vp.insert<path> ("config.config.save", true /* ovr */);
@@ -166,39 +149,11 @@ namespace build2
//
// Use the NULL value to clear.
//
- auto& c_p (vp.insert<vector<pair<string, string>>> (
- "config.config.persist", true /* ovr */, v_p));
-
- // Configuration environment variables.
- //
- // Environment variables used by tools (e.g., compilers), buildfiles
- // (e.g., $getenv()), and the build system itself (e.g., to locate
- // tools) in ways that affect the build result are in essence part of
- // the project configuration.
- //
- // This variable allows storing environment variable overrides that
- // should be applied to the environment when executing tools, etc., as
- // part of a project build. Specifically, it contains a list of
- // environment variable "sets" (<name>=<value>) and "unsets" (<name>).
- // If multiple entries are specified for the same environment variable,
- // the last entry has effect. For example:
- //
- // config.config.environment="LC_ALL=C LANG"
- //
- // Note that a subproject inherits overrides from its amalgamation (this
- // semantics is the result of the way we optimize the storage of this
- // variable in subproject's config.build; the thinking is that if a
- // variable is not overridden by the subproject then it doesn't affect
- // the build result and therefore it's irrelevant whether it has a value
- // that came from the original environment of from the amalgamation
- // override).
- //
- // Use the NULL or empty value to clear.
- //
- // @@ We could use =<name> as a "pass-through" instruction (e.g., if
- // we need to use original value in subproject).
+ // Note: must be entered during bootstrap since we need it in create's
+ // save_config().
//
- auto& c_e (vp.insert<strings> ("config.config.environment", true /* ovr */));
+ vp.insert<vector<pair<string, string>>> (
+ "config.config.persist", true /* ovr */, v_p);
// Only create the module if we are configuring, creating, or
// disfiguring or if it was requested with config.config.module (useful
@@ -229,11 +184,6 @@ namespace build2
//
m.save_module ("config", INT32_MIN);
m.save_module ("import", INT32_MIN);
-
- m.save_variable (c_p, save_null_omitted);
- m.save_variable (c_e,
- save_null_omitted | save_empty_omitted | save_base,
- &save_environment);
}
}
@@ -277,16 +227,106 @@ namespace build2
return true;
}
+ context& ctx (rs.ctx);
+
l5 ([&]{trace << "for " << rs;});
+ // If we have the module, then we are configuring (or the project wishes
+ // to call $config.save(); we don't get here on disfigure).
+ //
+ module* m (extra.module != nullptr
+ ? &extra.module_as<module> ()
+ : nullptr);
+
auto& vp (rs.var_pool ());
// Note: config.* is pattern-typed to global visibility.
//
const auto v_p (variable_visibility::project);
- auto& c_l (vp.insert<paths> ("config.config.load", true /* ovr */));
auto& c_v (vp.insert<uint64_t> ("config.version", false /*ovr*/, v_p));
+ auto& c_l (vp.insert<paths> ("config.config.load", true /* ovr */));
+
+ // Hermetic configurations.
+ //
+ // A hermetic configuration stores environment variables that affect the
+ // project in config.config.environment.
+ //
+ // Note that this is essentially a tri-state value: true means keep
+ // hermetizing (save the environment in config.config.environment),
+ // false means keep de-hermetizing (clear config.config.environment) and
+ // undefined/NULL means don't touch config.config.environment.
+ //
+ // During reconfiguration things stay hermetic unless re-hermetization
+ // is explicitly requested with config.config.hermetic.reload=true (or
+ // de-hermetization is requested with config.config.hermetic=false).
+ //
+ // Use the NULL value to clear.
+ //
+ auto& c_h (vp.insert<bool> ("config.config.hermetic", true /* ovr */));
+
+ if (m != nullptr)
+ m->save_variable (c_h, save_null_omitted);
+
+ // Request hermetic configuration re-hermetization.
+ //
+ // Note that this variable is not saved in config.build and is expected
+ // to always be specified as a command line override.
+ //
+ auto& c_h_r (
+ vp.insert<bool> ("config.config.hermetic.reload", true /* ovr */));
+
+ // Hermetic configuration environment variables inclusion/exclusion.
+ //
+ // This configuration variable can be used to include additional or
+ // exclude existing environment variables into/from the list that should
+ // be saved in order to make the configuration hermetic. For example:
+ //
+ // config.config.hermetic.environment="LANG PATH@false"
+ //
+ // Use the NULL or empty value to clear.
+ //
+ auto& c_h_e (
+ vp.insert<hermetic_environment> ("config.config.hermetic.environment"));
+
+ if (m != nullptr)
+ m->save_variable (c_h_e, save_null_omitted | save_empty_omitted);
+
+ // Configuration environment variables.
+ //
+ // Environment variables used by tools (e.g., compilers), buildfiles
+ // (e.g., $getenv()), and the build system itself (e.g., to locate
+ // tools) in ways that affect the build result are in essence part of
+ // the project configuration.
+ //
+ // This variable allows storing environment variable overrides that
+ // should be applied to the environment when executing tools, etc., as
+ // part of a project build. Specifically, it contains a list of
+ // environment variable "sets" (<name>=<value>) and "unsets" (<name>).
+ // If multiple entries are specified for the same environment variable,
+ // the last entry has effect. For example:
+ //
+ // config.config.environment="LC_ALL=C LANG"
+ //
+ // Note that a subproject inherits overrides from its amalgamation (this
+ // semantics is the result of the way we optimize the storage of this
+ // variable in subproject's config.build; the thinking is that if a
+ // variable is not overridden by the subproject then it doesn't affect
+ // the build result and therefore it's irrelevant whether it has a value
+ // that came from the original environment of from the amalgamation
+ // override).
+ //
+ // Use the NULL or empty value to clear.
+ //
+ // @@ We could use =<name> as a "pass-through" instruction (e.g., if
+ // we need to use original value in subproject).
+ //
+ auto& c_e (vp.insert<strings> ("config.config.environment", true /* ovr */));
+
+ if (m != nullptr)
+ m->save_variable (c_e,
+ save_null_omitted | save_empty_omitted | save_base,
+ &save_environment);
// Load config.build if one exists followed by extra files specified in
// config.config.load (we don't need to worry about disfigure since we
@@ -358,7 +398,7 @@ namespace build2
// b ./config.config.load=.../config.build # this project
// b !config.config.load=.../config.build # every project
//
- if (l.belongs (rs) || l.belongs (rs.ctx.global_scope))
+ if (l.belongs (rs) || l.belongs (ctx.global_scope))
{
for (const path& f: cast<paths> (l))
{
@@ -384,31 +424,50 @@ namespace build2
}
}
- // Cache the config.config.persist value, if any.
+ // Save and cache the config.config.persist value, if any.
//
- if (extra.module != nullptr)
+ if (m != nullptr)
{
- auto& m (extra.module_as<module> ());
+ auto& c_p (*vp.find ("config.config.persist"));
+ m->save_variable (c_p, save_null_omitted);
+ m->persist = cast_null<vector<pair<string, string>>> (rs[c_p]);
+ }
- m.persist =
- cast_null<vector<pair<string, string>>> (
- rs["config.config.persist"]);
+ // If we are configuring, handle config.config.hermetic.
+ //
+ // The overall plan is to either clear config.config.environment (if
+ // c.c.h=false) or populate it with the values that affect this project
+ // (if c.c.h=true). We have to do it half here (because c.c.e is used as
+ // a source for the project environment and we would naturally want the
+ // semantics to be equivalent to what will be saved in config.build) and
+ // half in configure_execute() (because that's where we have the final
+ // list of all the environment variables we need to save).
+ //
+ // So here we must deal with the cases where the current c.c.e value
+ // will be changed: either cleared (c.c.h=false) or set to new values
+ // from the "outer" environment (c.c.h.reload=true). Note also that even
+ // then a c.c.e value from an amalgamation, if any, should be in effect.
+ //
+ if (ctx.current_mif->id == configure_id &&
+ (!cast_true<bool> (rs[c_h]) || // c.c.h=false
+ cast_false<bool> (rs[c_h_r]))) // c.c.h.r=true
+ {
+ rs.vars.erase (c_e); // Undefine.
}
// Copy config.config.environment to scope::root_extra::environment.
//
// Note that we store shallow copies that point to the c.c.environment
- // value which means it shall not change.
+ // value which means it should not change.
//
- if (const strings* src = cast_null<strings> (
- rs["config.config.environment"]))
+ if (const strings* src = cast_null<strings> (rs[c_e]))
{
vector<const char*>& dst (rs.root_extra->environment);
// The idea is to only copy entries that are effective, that is those
// that actually override something in the environment. This should be
- // both more efficient and less noisy (e.g., if we decide to print
- // this in diagnostics).
+ // both more efficient and less noisy (e.g., if we need to print this
+ // in diagnostics).
//
// Note that config.config.environment may contain duplicates and the
// last entry should have effect.
@@ -429,7 +488,8 @@ namespace build2
if (find_if (src->rbegin (), i,
[&v, p] (const string& v1)
{
- return compare_env (v, p, v1, v1.find ('='));
+ return saved_environment::compare (
+ v, v1, p, v1.find ('='));
}) != i)
continue;
diff --git a/libbuild2/config/module.hxx b/libbuild2/config/module.hxx
index b8b5d07..92fed32 100644
--- a/libbuild2/config/module.hxx
+++ b/libbuild2/config/module.hxx
@@ -4,6 +4,8 @@
#ifndef LIBBUILD2_CONFIG_MODULE_HXX
#define LIBBUILD2_CONFIG_MODULE_HXX
+#include <cstring> // strncmp()
+
#include <libbutl/prefix-map.mxx>
#include <libbuild2/types.hxx>
@@ -50,7 +52,7 @@ namespace build2
const_iterator
find (const variable& var) const
{
- return std::find_if (
+ return find_if (
begin (),
end (),
[&var] (const saved_variable& v) {return var == v.var;});
@@ -76,8 +78,69 @@ namespace build2
}
};
- struct module: build2::module
+ // List of environment variable names that effect this project.
+ //
+ // Note that on Windows environment variable names are case-insensitive.
+ //
+ struct saved_environment: vector<string>
{
+ // Compare environment variable names.
+ //
+ static inline bool
+ compare (const string& x,
+ const string& y,
+ size_t xn = string::npos,
+ size_t yn = string::npos)
+ {
+ if (xn == string::npos) xn = x.size ();
+ if (yn == string::npos) yn = y.size ();
+
+ return xn == yn &&
+#ifdef _WIN32
+ icasecmp (x.c_str (), y.c_str (), xn) == 0
+#else
+ strncmp (x.c_str (), y.c_str (), xn) == 0
+#endif
+ ;
+ }
+
+ iterator
+ find (const string& v)
+ {
+ return find_if (
+ begin (),
+ end (),
+ [&v] (const string& v1) {return compare (v, v1);});
+ }
+
+ const_iterator
+ find (const string& v) const
+ {
+ return find_if (
+ begin (),
+ end (),
+ [&v] (const string& v1) {return compare (v, v1);});
+ }
+
+ void
+ insert (string v)
+ {
+ if (find (v) == end ())
+ push_back (move (v));
+ }
+
+ void
+ erase (const string& v)
+ {
+ auto i (find (v));
+ if (i != end ())
+ vector<string>::erase (i);
+ }
+ };
+
+ class module: public build2::module
+ {
+ public:
config::saved_modules saved_modules;
// Return true if variable/module were newly inserted.
@@ -110,6 +173,9 @@ namespace build2
return nullptr;
}
+ config::saved_environment saved_environment;
+ strings old_environment;
+
// Configure/disfigure hooks.
//
static bool
diff --git a/libbuild2/config/operation.cxx b/libbuild2/config/operation.cxx
index c5e8004..760f998 100644
--- a/libbuild2/config/operation.cxx
+++ b/libbuild2/config/operation.cxx
@@ -157,24 +157,19 @@ namespace build2
// If inherit is false, then don't rely on inheritance from outer scopes.
//
+ // @@ We are modifying the module (marking additional variables as saved)
+ // and this function can be called from a buildfile (probably only
+ // during serial execution but still).
+ //
void
save_config (const scope& rs,
ostream& os, const path_name& on,
bool inherit,
+ module& mod,
const project_set& projects)
{
context& ctx (rs.ctx);
- // @@ We are modifying the module (marking additional variables as
- // saved) and this function can be called from a buildfile (probably
- // only during serial execution but still).
- //
- module* mod (rs.find_module<module> (module::name));
-
- if (mod == nullptr)
- fail (on) << "no configuration information available during this "
- << "meta-operation";
-
names storage;
auto info_value = [&storage] (diag_record& dr, const value& v) mutable
@@ -234,18 +229,18 @@ namespace build2
var->name.compare (0, 14, "config.config.") == 0)
continue;
- if (mod->find_variable (*var)) // Saved or unsaved.
+ if (mod.find_variable (*var)) // Saved or unsaved.
continue;
const value& v (p.first->second);
pair<bool, bool> r (save_config_variable (*var,
- mod->persist,
+ mod.persist,
false /* inherited */,
true /* unused */));
if (r.first) // save
{
- mod->save_variable (*var, 0);
+ mod.save_variable (*var, 0);
if (r.second) // warn
{
@@ -281,7 +276,7 @@ namespace build2
// Save config variables.
//
- for (auto p: mod->saved_modules.order)
+ for (auto p: mod.saved_modules.order)
{
const string& sname (p.second->first);
const saved_variables& svars (p.second->second);
@@ -542,6 +537,7 @@ namespace build2
save_config (const scope& rs,
const path& f,
bool inherit,
+ module& mod,
const project_set& projects)
{
path_name fn (f);
@@ -555,7 +551,8 @@ namespace build2
try
{
ofdstream ofs;
- save_config (rs, open_file_or_stdout (fn, ofs), fn, inherit, projects);
+ save_config (
+ rs, open_file_or_stdout (fn, ofs), fn, inherit, mod, projects);
ofs.close ();
}
catch (const io_error& e)
@@ -564,10 +561,81 @@ namespace build2
}
}
+ // Update config.config.environment value for a hermetic configuration.
+ //
+ static void
+ save_environment (scope& rs, module& mod)
+ {
+ // Here we have two parts: (1) get the list of environment variables we
+ // need to save and (2) save their values in config.config.environment.
+ //
+ // The saved_environment list should by now contain all the project-
+ // specific environment variables. To that we add builtin defaults and
+ // then filter the result against config.config.hermetic.environment
+ // inclusions/exclusions.
+ //
+ auto& vars (mod.saved_environment);
+
+ vars.insert ("PATH");
+
+#if defined(_WIN32)
+#elif defined(__APPLE__)
+ vars.insert ("DYLD_LIBRARY_PATH");
+#else // Linux, FreeBSD, NetBSD, OpenBSD
+ vars.insert ("LD_LIBRARY_PATH");
+#endif
+
+ for (const pair<string, optional<bool>>& p:
+ cast_empty<hermetic_environment> (
+ rs["config.config.hermetic.environment"]))
+ {
+ if (!p.second || *p.second)
+ vars.insert (p.first);
+ else
+ vars.erase (p.first);
+ }
+
+ // Get the values.
+ //
+ strings vals;
+ {
+ // Set the project environment before querying the values. Note that
+ // the logic in init() makes sure that this is all we need to do to
+ // handle reload (in which case we should still be using
+ // config.config.environment from amalgamation, if any).
+ //
+ auto_project_env penv (rs);
+
+ for (const string& var: vars)
+ {
+ if (optional<string> val = getenv (var))
+ {
+ vals.push_back (var + '=' + *val);
+ }
+ else
+ vals.push_back (var); // Unset.
+ }
+ }
+
+ value& v (rs.assign (*rs.ctx.var_pool.find ("config.config.environment")));
+
+ // Note that setting new config.config.environment value invalidates the
+ // project's environment (scope::root_extra::environment) which could be
+ // queried in the post-configuration hook. We could re-initialize it but
+ // the c.c.e value from amalgamation could be referenced by subprojects.
+ // So instead it seems easier to just save the old value in the module.
+ //
+ if (v)
+ mod.old_environment = move (v.as<strings> ());
+
+ v = move (vals);
+ }
+
static void
configure_project (action a,
- const scope& rs,
+ scope& rs,
const variable* c_s, // config.config.save
+ module& mod,
project_set& projects)
{
tracer trace ("configure_project");
@@ -597,6 +665,12 @@ namespace build2
{
l5 ([&]{trace << "completely configuring " << out_root;});
+ // Save the environment if this configuration is hermetic (see init()
+ // for the other half of this logic).
+ //
+ if (cast_false<bool> (rs["config.config.hermetic"]))
+ save_environment (rs, mod);
+
// Save src-root.build unless out_root is the same as src.
//
if (c_s == nullptr && out_root != src_root)
@@ -621,7 +695,7 @@ namespace build2
// may end up leaving it in partially configured state.
//
if (c_s == nullptr)
- save_config (rs, config_file (rs), true /* inherit */, projects);
+ save_config (rs, config_file (rs), true /* inherit */, mod, projects);
else
{
lookup l (rs[*c_s]);
@@ -634,7 +708,8 @@ namespace build2
// still want to support this mode somehow in the future (it seems
// like an override of config.config.persist should do the trick).
//
- save_config (rs, cast<path> (l), false /* inherit */, projects);
+ save_config (
+ rs, cast<path> (l), false /* inherit */, mod, projects);
}
}
}
@@ -645,11 +720,8 @@ namespace build2
if (c_s == nullptr)
{
- if (module* m = rs.find_module<module> (module::name))
- {
- for (auto hook: m->configure_post_)
- hook (a, rs);
- }
+ for (auto hook: mod.configure_post_)
+ hook (a, rs);
}
// Configure subprojects that have been loaded.
@@ -660,15 +732,19 @@ namespace build2
{
const dir_path& pd (p.second);
dir_path out_nroot (out_root / pd);
- const scope& nrs (ctx.scopes.find_out (out_nroot));
+ scope& nrs (ctx.scopes.find_out (out_nroot).rw ());
- // @@ Strictly speaking we need to check whether the config module
- // was loaded for this subproject.
+ // Skip this subproject if it is not loaded or doesn't use the
+ // config module.
//
- if (nrs.out_path () != out_nroot) // This subproject not loaded.
- continue;
+ if (nrs.out_path () == out_nroot)
+ {
+ if (module* m = rs.find_module<module> (module::name))
+ {
+ configure_project (a, nrs, c_s, *m, projects);
+ }
+ }
- configure_project (a, nrs, c_s, projects);
}
}
}
@@ -874,7 +950,11 @@ namespace build2
}
}
- configure_project (a, *rs, c_s, projects);
+ configure_project (a,
+ rs->rw (),
+ c_s,
+ *rs->find_module<module> (module::name),
+ projects);
}
}
}
diff --git a/libbuild2/config/operation.hxx b/libbuild2/config/operation.hxx
index a887eb7..ded3c8b 100644
--- a/libbuild2/config/operation.hxx
+++ b/libbuild2/config/operation.hxx
@@ -15,6 +15,8 @@ namespace build2
{
namespace config
{
+ class module;
+
extern const meta_operation_info mo_configure;
extern const meta_operation_info mo_disfigure;
@@ -37,7 +39,12 @@ namespace build2
save_config (const scope& rs,
ostream&, const path_name&,
bool inherit,
+ module&,
const project_set&);
+
+ // See config.config.hermetic.environment.
+ //
+ using hermetic_environment = vector<pair<string, optional<bool>>>;
}
}
diff --git a/libbuild2/variable.cxx b/libbuild2/variable.cxx
index 917b9e7..efda63d 100644
--- a/libbuild2/variable.cxx
+++ b/libbuild2/variable.cxx
@@ -1759,6 +1759,14 @@ namespace build2
return pair<value&, bool> (r, p.second);
}
+ bool variable_map::
+ erase (const variable& var)
+ {
+ assert (!global_ || ctx->phase == run_phase::load);
+
+ return m_.erase (var) != 0;
+ }
+
// variable_type_map
//
lookup variable_type_map::
diff --git a/libbuild2/variable.hxx b/libbuild2/variable.hxx
index 898648c..d59a891 100644
--- a/libbuild2/variable.hxx
+++ b/libbuild2/variable.hxx
@@ -1562,6 +1562,14 @@ namespace build2
pair<value_data*, const variable&>
lookup_to_modify (const variable&, bool typed = true);
+ pair<const_iterator, const_iterator>
+ lookup_namespace (const variable& ns) const
+ {
+ auto r (m_.find_sub (ns));
+ return make_pair (const_iterator (r.first, *this),
+ const_iterator (r.second, *this));
+ }
+
// Convert a lookup pointing to a value belonging to this variable map
// to its non-const version. Note that this is only safe on the original
// values (see find_original()).
@@ -1599,13 +1607,10 @@ namespace build2
pair<value&, bool>
insert (const variable&, bool typed = true);
- pair<const_iterator, const_iterator>
- lookup_namespace (const variable& ns) const
- {
- auto r (m_.find_sub (ns));
- return make_pair (const_iterator (r.first, *this),
- const_iterator (r.second, *this));
- }
+ // Note: does not deal with aliases.
+ //
+ bool
+ erase (const variable&);
const_iterator
begin () const {return const_iterator (m_.begin (), *this);}