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[mingw/mingw-get.git] / src / pkgdeps.cpp

/*
 * pkgdeps.cpp
 *
 * $Id$
 *
 * Written by Keith Marshall <keithmarshall@users.sourceforge.net>
 * Copyright (C) 2009, 2010, 2011, 2012, MinGW Project
 *
 *
 * Implementation of the package dependency resolver method, of the
 * "pkgXmlDocument" class; includes the interface to the action item
 * task scheduler, which is called to ensure that processing for any
 * identified prerequisite packages is appropriately scheduled.
 *
 *
 * This is free software.  Permission is granted to copy, modify and
 * redistribute this software, under the provisions of the GNU General
 * Public License, Version 3, (or, at your option, any later version),
 * as published by the Free Software Foundation; see the file COPYING
 * for licensing details.
 *
 * Note, in particular, that this software is provided "as is", in the
 * hope that it may prove useful, but WITHOUT WARRANTY OF ANY KIND; not
 * even an implied WARRANTY OF MERCHANTABILITY, nor of FITNESS FOR ANY
 * PARTICULAR PURPOSE.  Under no circumstances will the author, or the
 * MinGW Project, accept liability for any damages, however caused,
 * arising from the use of this software.
 *
 */
#include <string.h>

#include "dmh.h"
#include "debug.h"

#include "pkginfo.h"
#include "pkgbase.h"
#include "pkgkeys.h"
#include "pkgtask.h"
#include "pkgopts.h"

/* Define supplementary action codes, which may be used exclusively
 * by pkgXmlDocument::ResolveDependencies(), to ensure that recursive
 * actions are appropriately scheduled; these apply to user specified
 * actions "upgrade --recursive", "install --recursive --reinstall",
 * and "upgrade --recursive --reinstall" respectively.
 */
#define ACTION_RECURSIVE_UPGRADE        (ACTION_UPGRADE | OPTION_RECURSIVE)
#define ACTION_RECURSIVE_REINSTALL      (ACTION_INSTALL | OPTION_ALL_DEPS)
#define ACTION_RECURSIVE_REPLACE        (ACTION_UPGRADE | OPTION_ALL_DEPS)

/* FIXME: the following declaration belongs in a future "pkgmsgs.h"
 * header file, with the function implementation in a separate C or C++
 * messages source file, with appropriate internationalisation...
 */
EXTERN_C const char *pkgMsgUnknownPackage( void );

const char *pkgMsgUnknownPackage( void )
{
  /* FIXME: (see note above); return English language only, for now.
   */
  return "%s: unknown package\n";
}

/* Provide a convenience macro for declaring static inline functions
 * which we want to always expand inline.
 */
#define STATIC_INLINE   static inline __attribute__((__always_inline__))

static bool is_installed( pkgXmlNode *release )
{
  /* Helper to check installation status of a specified package release.
   */
  const char *status;
  /*
   * First, check for any 'installed' attribute which may have been
   * explicitly specified for the 'release' record...
   */
  if( (status = release->GetPropVal( installed_key, NULL )) != NULL )
    /*
     * ...immediately returning the status deduced from it,
     * when present.
     */
    return (strcmp( status, yes_value ) == 0);

  /* When the package definition itself doesn't bear an explicit
   * 'installed' attribute, then we must check the system map for
   * an associated installation record...
   */
  const char *pkgname;
  if( ((pkgname = release->GetPropVal( tarname_key, NULL )) != NULL)
  &&   (release->GetInstallationRecord( pkgname ) != NULL)  )
  {
    /* ...and, when one is found, we can mark this package with
     * an explicit status attribute for future reference, before
     * we return confirmation of the installed status...
     */
    release->SetAttribute( installed_key, yes_value );
    return true;
  }

  /* If we get to here, we may deduce that the package is not
   * installed; once again, we set the explicit attribute value
   * to convey this for future reference, before returning the
   * appropriate status flag.
   */
  release->SetAttribute( installed_key, no_value );
  return false;
}

pkgXmlNode *pkgXmlNode::GetInstallationRecord( const char *pkgname )
{
  /* Retrieve the installation record, if any, for the package
   * specified by fully qualified canonical 'pkgname'.
   *
   * First, break down the specified package name, and retrieve
   * the sysroot database entry for its associated subsystem.
   */
  pkgXmlNode *sysroot;
  pkgSpecs lookup( pkgname );
  if( (sysroot = GetSysRoot( lookup.GetSubSystemName() )) != NULL )
  {
    /* We successfully retrieved a sysroot entry; now we must
     * search the associated list of installed packages, for one
     * with the appropriate canonical package name.
     */
    pkgXmlNode *pkg = sysroot->FindFirstAssociate( installed_key );
    while( pkg != NULL )
    {
      /* We found an installed package entry; check if it has
       * the correct canonical name...
       */
      const char *installed = pkg->GetPropVal( tarname_key, NULL );
      if( (installed != NULL) && (strcmp( installed, pkgname ) == 0) )
        /*
         * ...returning this entry if so...
         */
        return pkg;

      /* ...otherwise, move on to the next entry, if any.
       */
      pkg = pkg->FindNextAssociate( installed_key );
    }
  }

  /* If we get to here, we didn't find an entry for the required
   * package; return NULL, indicating that it is not installed.
   */
  return NULL;
}

const char *pkgXmlNode::GetContainerAttribute( const char *key, const char *sub )
{
  /* Walk the XML path from current element, back towards the document root,
   * until we find the innermost element which has an attribute matching "key";
   * if such an element is found, return the value of the attribute; if we have
   * traversed the entire path, all the way to the document root, and we have
   * not found any element with the "key" attribute, return "sub".
   */
  pkgXmlNode *pkg = this;
  pkgXmlNode *root = pkg->GetDocumentRoot();
  while( pkg != NULL )
  {
    /* We haven't yet tried to search beyond the document root;
     * try matching "key" to an attribute of the current element...
     */
    const char *retval = pkg->GetPropVal( key, NULL );
    if( retval != NULL )
      /*
       * ...returning its value, if such an attribute is found...
       */
      return retval;

    /* ...otherwise,
     * take a further step back towards the document root.
     */
    pkg = (pkg == root) ? NULL : pkg->GetParent();
  }

  /* If we get to here, then no element with the required "key"
   * attribute could be found; substitute the specified default.
   */
  return sub;
}

DEBUG_INVOKED static int indent = -1;

DEBUG_INVOKED static void
DEBUG_INVOKED show_required( pkgSpecs *req )
DEBUG_INVOKED {
DEBUG_INVOKED   const char *tarname = NULL;
DEBUG_INVOKED   dmh_printf( "%*s require: %s\n", indent, "", req->GetTarName( tarname ) );
DEBUG_INVOKED   free( (void *)(tarname) );
DEBUG_INVOKED }

static inline
bool is_abi_compatible( pkgSpecs *refdata, const char *version )
{
  /* Local helper, used by pkgXmlDocument::ResolveDependencies(),
   * to confirm that the ABI identification number of a selected
   * component package is an exact match to a requirement spec.
   */
  const char *ref_version;
  if( (ref_version = refdata->GetComponentVersion()) == NULL )
    /*
     * Here, confirm that both are unversioned...
     */
    return (version == NULL);

  /* ...otherwise, fall through to check that both bear IDENTICALLY
   * the same ABI version number.
   */
  return ((version != NULL) && (strcmp( version, ref_version ) == 0));
}

STATIC_INLINE unsigned long action_class
( unsigned long requested, unsigned long viable )
{
  /* Helper function for use by pkgXmlDocument::ResolveDependencies();
   * it classifies each requested action with respect to any previously
   * installed version of each package, to ensure that reinstallation
   * and recursive requests are dispatched appropriately.
   */
  return viable ? requested : ACTION_RECURSIVE_UPGRADE;
}

STATIC_INLINE unsigned long with_request_flags( unsigned long request )
{
  /* Helper function for use by pkgXmlDocument::ResolveDependencies();
   * it isolates the request flags from the action code, to accommodate
   * promotion of an alternative action with matching flags.
   */
  return request & ~(ACTION_MASK | ACTION_DOWNLOAD);
}

STATIC_INLINE unsigned long with_download( unsigned long action_code )
{
  /* Helper function for use by pkgXmlDocument::ResolveDependencies();
   * it adds the download request flag,when promoting any action which
   * may require a package archive to be downloaded.
   */
  return  action_code | (ACTION_DOWNLOAD);
}

STATIC_INLINE unsigned long promote
( unsigned long request, unsigned long action_code )
{
  /* Helper function for use by pkgXmlDocument::ResolveDependencies();
   * it promotes an alternative action to that explicitly requested by
   * the user, when this is necessary to satisfy a dependency.
   */
  return with_request_flags( request ) | with_download( action_code );
}

void
pkgXmlDocument::ResolveDependencies( pkgXmlNode* package, pkgActionItem* rank )
{
  /* For the specified "package", (nominally a "release"), identify its
   * prerequisites, (as specified by "requires" tags), and schedule actions
   * to process them; repeat recursively, to identify further dependencies
   * of such prerequisites, and finally, extend the search to capture
   * additional dependencies common to the containing package group.
   */
  pkgSpecs *refdata = NULL;
  pkgXmlNode *refpkg = package;

  DEBUG_INVOKED ++indent;

  /* Capture the state of global option settings controlling the scope
   * of recursive behaviour and reinstallation requests, so that we may
   * implicitly extend the effect when processing virtual packages...
   */
  int request_mode = pkgOptions()->Test( OPTION_ALL_DEPS );
  if( match_if_explicit( package->ArchiveName(), value_none ) )
    /*
     * ...such that the effect of an upgrade or a reinstall implicitly
     * applies, through a single level of recursion, to the first level
     * of requisite dependencies.
     */
    request_mode |= OPTION_RECURSIVE;
  request_mode |= request & ACTION_MASK;

  while( package != NULL )
  {
    /* We have a valid XML entity, which may identify dependencies;
     * check if it includes any "requires" specification...
     */
    pkgXmlNode *dep = package->FindFirstAssociate( requires_key );
    while( dep != NULL )
    {
      /* We found a dependency specification...
       * Initially, assume this package is not installed.
       */
      pkgXmlNode *installed = NULL;
      unsigned installed_is_viable = 0;

      /* To facilitate resolution of "%" version matching wildcards
       * in the requirements specification, we need to parse the version
       * specification for the current dependent package...
       */
      if( refdata == NULL )
      {
        /* ...but we deferred that until we knew for sure that it would
         * be needed; it is, so parse it now.
         */
        const char *refname;
        if( (refname = refpkg->GetPropVal( tarname_key, NULL )) != NULL )
        {
          DEBUG_INVOKE_IF( DEBUG_REQUEST( DEBUG_TRACE_DEPENDENCIES ),
              dmh_printf( "%*s%s: resolve dependencies\n", indent, "", refname )
            );
          refdata = new pkgSpecs( refname );
        }
      }

      /* Identify the prerequisite package, from its canonical name...
       */
      pkgActionItem wanted; pkgXmlNode *selected;
      pkgSpecs req( wanted.SetRequirements( dep, refdata ) );
      DEBUG_INVOKE_IF( DEBUG_REQUEST( DEBUG_TRACE_DEPENDENCIES ),
          show_required( &req )
        );
      /*
       * (Both the package name, and subsystem if specified, must match)...
       */
      selected = FindPackageByName( req.GetPackageName(), req.GetSubSystemName() );

      /* When we've identified the appropriate package...
       */
      if( selected != NULL )
      {
        /* ...and, more significantly, the appropriate component package,
         * where applicable...
         */
        pkgXmlNode *component; const char *reqclass;
        if( (reqclass = req.GetComponentClass()) == NULL )
          reqclass = value_unknown;

        if( (component = selected->FindFirstAssociate( component_key )) == NULL )
          /*
           * ...but if no separate component package exists,
           * consider the parent package itself, as sole component.
           */
          component = selected;

        /* At this point, we have no more than a tentative package selection;
         * it may not provide a component to fit the requirements specification.
         * Thus, kill the selection, pending reaffirmation...
         */
        selected = NULL;
        while( component != NULL )
        {
          /* ...by stepping through the "releases" of this component package...
          */
          pkgXmlNode *required = component->FindFirstAssociate( release_key );
          while( required != NULL )
          {
            /* ...noting if we find one already marked as "installed"...
            */
            const char *tstclass;
            DEBUG_INVOKED const char *already_installed = "";
            pkgSpecs tst( tstclass = required->GetPropVal( tarname_key, NULL ) );
            DEBUG_INVOKE_IF( DEBUG_REQUEST( DEBUG_TRACE_DEPENDENCIES ),
                dmh_printf( "%*s  considering: %s", indent, "", tstclass )
              );
            if( (tstclass = tst.GetComponentClass()) == NULL )
              tstclass = value_unknown;

            if( is_installed( required ) && (strcmp( tstclass, reqclass ) == 0)
            /*
             * We found an installed version of the requisite component,
             * but we ignore it unless it is ABI version compatible with
             * the version we need; (the intent of ABI versioning is to
             * accommodate multiple concurrent installations of shared
             * objects supporting the differing ABI specifications).
             */
            &&  is_abi_compatible( &tst, req.GetComponentVersion() )  )
            {
              installed = required;
              DEBUG_INVOKED already_installed = " (already installed)";
            }
            /* ...and identify the most suitable candidate "release"
             * to satisfy the current dependency...
             */
            if( wanted.SelectIfMostRecentFit( required ) == required )
              selected = component = required;

            if( required == installed )
              installed_is_viable = wanted.HasAttribute( ACTION_MAY_SELECT );

            DEBUG_INVOKE_IF( DEBUG_REQUEST( DEBUG_TRACE_DEPENDENCIES ),
                dmh_printf( "%s%s\n", wanted.HasAttribute( ACTION_MAY_SELECT )
                  ? ": viable candidate"
                  : "",
                  already_installed
                )
              );

            /* ...continuing, until all available "releases"
             * have been evaluated accordingly.
             */
            required = required->FindNextAssociate( release_key );
          }

          /* Where multiple component packages do exist,
           * continue until all have been inspected.
           */
          component = component->FindNextAssociate( component_key );
        }

        /* We have now identified the most suitable candidate package,
         * to resolve the current dependency...
         */
        if( installed )
        {
          /* ...this package is already installed, so we may schedule
           * a resolved dependency match, with no pending action...
           */
          unsigned long fallback = with_request_flags( request );
          switch( action_class( request_mode, installed_is_viable ) )
          {
            /* ...except that...
             */
            case ACTION_RECURSIVE_REINSTALL:
              /*
               * ...when the action is "install", with "--reinstall"
               * and "--recursive" options in effect, we update the
               * package selection to favour the already installed
               * version over any available upgrade...
               */
              wanted.SelectPackage( selected = installed );
              /*
               * ...falling through to...
               */

            case ACTION_RECURSIVE_REPLACE:
            case ACTION_RECURSIVE_UPGRADE:
              /*
               * ...schedule removal of the already installed version,
               * for replacement by a fresh copy of the same version,
               * or an upgraded version, as appropriate.
               */
              DEBUG_INVOKE_IF( DEBUG_REQUEST( DEBUG_TRACE_DEPENDENCIES ),
                  dmh_printf( "%*s%s: schedule replacement\n", indent + 2, "",
                      installed->GetPropVal( tarname_key, value_unknown )
                    )
                );
              wanted.SelectPackage( installed, to_remove );
              fallback |= with_download( ACTION_UPGRADE );
              break;

            default:
              /* In any other case, the currently installed version is
               * to be left in place; we must ensure that its dependencies,
               * (if any), will be resolved with respect to this already
               * installed version.
               */
              wanted.SelectPackage( selected = installed );
          }

          /* Schedule the appropriate fallback action, (which may be none),
           * for the already installed package.
           */
          rank = Schedule( fallback, wanted, rank );
        }

#       if 0
        /* FIXME: this change in logic may introduce a regression; I (KDM)
         * may need to re-evaluate the conceptual effect of PRIMARY actions
         * vs. SECONDARY actions in this context, but this pre-v0.5 logic
         * breaks the handling of meta-packages in v0.5
         */
        else if( ((request & ACTION_MASK) == ACTION_INSTALL)
          /*
           * The required package is not installed, so when
           * we are performing an installation, ...
           */
        || ((request & (ACTION_PRIMARY | ACTION_INSTALL)) == ACTION_INSTALL) )
#       endif
        else if( (request & ACTION_INSTALL) == ACTION_INSTALL )
        {
          /* ...or when this is a new requirement of a package
           * which is being upgraded, then we must schedule it
           * for installation now; (we may simply ignore it, if
           * we are performing a removal).
           */
          DEBUG_INVOKE_IF( DEBUG_REQUEST( DEBUG_TRACE_DEPENDENCIES ),
              dmh_printf( "%*s%s: schedule installation (flags=0x%08x)\n",
                  indent + 2, "", selected->GetPropVal( tarname_key, value_unknown ),
                  promote( request, ACTION_INSTALL )
                )
            );
          rank = Schedule( promote( request, ACTION_INSTALL ), wanted, rank );
        }

        /* Regardless of the action scheduled, we must recursively
         * consider further dependencies of the resolved prerequisite;
         * FIXME: do we need to do this, when performing a removal?
         * Right now, I (KDM) don't think so...
         */
        if( (request & ACTION_INSTALL) != 0 )
          ResolveDependencies( selected, rank );
      }

      if( selected == NULL )
      {
        /* No package matching the selection criteria could be found;
         * report a dependency resolution failure in respect of each
         * specified criterion...
         */
        const char *ref, *key[] = { lt_key, le_key, eq_key, ge_key, gt_key };
        const char *requestor = refpkg->GetPropVal( tarname_key, value_unknown );

        dmh_control( DMH_BEGIN_DIGEST );
        dmh_notify( DMH_ERROR, "%s: requires...\n", requestor );
        for( int i = 0; i < sizeof( key ) / sizeof( char* ); i++ )
          if( (ref = dep->GetPropVal( key[i], NULL )) != NULL )
          {
            dmh_notify( DMH_ERROR, "%s: unresolved dependency (type '%s')\n", ref, key[i] );
            dmh_notify( DMH_ERROR, "%s: cannot identify any providing package\n" );
          }
        dmh_notify( DMH_ERROR, "please report this to the package maintainer\n" );
        dmh_control( DMH_END_DIGEST );
      }

      /* Continue, until all prerequisites of the current package
       * have been evaluated.
       */
      dep = dep->FindNextAssociate( requires_key );
    }
    /* Also consider any dependencies which may be common to
     * all releases, or all components, of the current package;
     * we do this by walking back through the XML hierarchy,
     * searching for "requires" elements in all containing
     * contexts, until we reach the root element.
     */
    package = (package == GetRoot()) ? NULL : package->GetParent();
  }
  DEBUG_INVOKED --indent;
  delete refdata;
}

STATIC_INLINE bool if_noref( const char *name )
{
  /* Helper function, used exclusively by the following assert_unmatched()
   * function; it is used to confirm that "name" represents nothing.
   */
  return (name == NULL) || (*name == '\0');
}

STATIC_INLINE bool if_match( const char *ref, const char *name )
{
  /* Helper function, used exclusively by the following assert_unmatched()
   * function; it is used to confirm that the package identified by "name"
   * is an exact match for that represented by "ref".
   */
  return (name != NULL) && (strcmp( ref, name ) == 0);
}

STATIC_INLINE bool if_alias( const char *ref, const char *list )
{
  /* Helper function, used exclusively by the following assert_unmatched()
   * function; it is used to confirm that the "list" of package name aliases
   * includes one which is an exact match for "ref".
   */
  return (list != NULL) && has_keyword( ref, list );
}

STATIC_INLINE bool assert_unmatched
( const char *ref, const char *val, const char *name, const char *alias )
{
  /* Helper for the following "assert_installed" function; it determines if
   * the reference name specified by "ref" matches either the corresponding
   * field value "val" from a tarname look-up, or in the case of a package
   * name reference, the containing package "name" attribute or any of its
   * specified "alias" names.  The return value is false, in the case of a
   * match, or true when unmatched.
   */
  return (ref == NULL)

    ? /* When "ref" is NULL, then a match requires all specified candidates
       * for matching to also be NULL, or to be pointers to empty strings.
       */
      !( if_noref( val ) && if_noref( name ) && if_noref( alias ))

    : /* Otherwise, when "ref" is not NULL, then a match is identified when
       * any one candidate is found to match.
       */
      !( if_match( ref, val ) || if_match( ref, name ) || if_alias( ref, alias ));
}

static
pkgXmlNode *assert_installed( pkgXmlNode *current, pkgXmlNode *installed )
{
  /* Validation hook for pkgXmlDocument::Schedule(); it checks for
   * possible prior installation of an obsolete version of a current
   * package, (i.e. the package itself is listed in the distribution
   * manifest, but the listing for the installed version has been
   * removed).
   *
   * Note that, by the time this helper is called, an installation
   * may have been identified already, by a release reference which
   * is still present in the distribution manifest; we perform this
   * check, only if no such identification was possible.
   */
  if( current && (installed == NULL) )
  {
    /* This is the specific case where we have selected a current
     * package for processing, but we HAVE NOT been able to identify
     * a prior installation through a distribution manifest reference;
     * thus, we must perform the further check for prior installation
     * of an obsolete version.
     *
     * Starting from the sysroot record for the specified release...
     */
    pkgXmlNode *sysroot; const char *tarname;
    pkgSpecs lookup( current->GetPropVal( tarname_key, NULL ) );
    if( (sysroot = current->GetSysRoot( lookup.GetSubSystemName() )) != NULL )
    {
      /* ...identify the first, if any, package installation record.
       */
      pkgXmlNode *ref = sysroot->FindFirstAssociate( installed_key );
      if( ref != NULL )
      {
        /* When at least one installation record exists,
         * establish references for the "tarname" fields which
         * we must match, to identify a prior installation.
         */
        const char *refname = lookup.GetPackageName();
        const char *cptname = lookup.GetComponentClass();
        const char *version = lookup.GetComponentVersion();

        /* Also identify the formal name for the containing package,
         * and any aliases by which it may also be known, so that we
         * may be able to identify a prior installation which may
         * have borne a deprecated package name.
         */
        const char *pkgname = current->GetContainerAttribute( name_key );
        const char *alias = current->GetContainerAttribute( alias_key );

        /* For each candidate installation record found...
         */
        while( ref != NULL )
        {
          /* ...check if it matches the look-up criteria.
           */
          pkgSpecs chk( tarname = ref->GetPropVal( tarname_key, NULL ) );
          if( assert_unmatched( chk.GetPackageName(), refname, pkgname, alias )
          ||  assert_unmatched( chk.GetComponentClass(), cptname, NULL, NULL )
          ||  assert_unmatched( chk.GetComponentVersion(), version, NULL, NULL )  )
            /*
             * This candidate isn't a match; try the next, if any...
             */
            ref = ref->FindNextAssociate( installed_key );

          else
          { /* We found a prior installation of a deprecated version;
             * back-build a corresponding reference within the associated
             * package or component-package inventory, in the internal
             * copy of the distribution manifest...
             */
            if( (installed = new pkgXmlNode( release_key )) != NULL )
            {
              installed->SetAttribute( tarname_key, tarname );
              installed->SetAttribute( installed_key, value_yes );
              if( (ref = current->GetParent()) != NULL )
                installed = ref->AddChild( installed );
            }
            /* Having found a prior installation, there is no need to
             * check any further installation records; force "ref" to
             * NULL, to inhibit further searching.
             */
            ref = NULL;
          }
        }
      }
    }
  }
  /* However we get to here, we always return the pointer to the installed
   * package entry identified by the dependency resolver, which may, or may
   * not have been modified by this function.
   */
  return installed;
}

void pkgActionItem::ConfirmInstallationStatus()
{
  /* Set the "to_remove" selection in an action item to match the installed
   * package entry, even when the release in question is no longer enumerated
   * in the package catalogue; (used to identify any installed version when
   * compiling a package reference listing).
   */
  selection[to_remove]
    = assert_installed( selection[to_install], selection[to_remove] );
}

static inline
const char *get_version_bounds( const char *name )
{
  /* Helper to locate any version bounds specification which may
   * have been appended to a package name command line argument.
   */
  if( (name != NULL) && *name )
    /*
     * If the name is specified, and not zero-length, then
     * the bounds specification begins at the first '<', '=',
     * or '>' character, (if any)...
     */
    do { if( (*name == '<') || (*name == '=') || (*name == '>') )
           /*
            * ...in which case, we return that location.
            */
           return name;
       } while( *++name );

  /* Otherwise we fall through, returning NULL to indicate
   * that no bounds specification is present.
   */
  return NULL;
}

void pkgActionItem::ApplyBounds( pkgXmlNode *release, const char *bounds )
{
  /* Method to interpret a user specified version requirement,
   * and attach it to a primary action item, much as if it were
   * an internally identified requirement, as identified by the
   * dependency resolver.
   */
  const char *refname;
  pkgSpecs refspec( release );

  while( (bounds != NULL) && *bounds )
  {
    /* Parse the user specified requirement, formulating a specification
     * which may be interpreted by "pkginfo"; (use an arbitrary package
     * name of "x", since we care only about the version number)...
     */
    const char *condition = NULL;
    char spec_string[7 + strlen( bounds )]; strcpy( spec_string, "x-" );
    char *p = spec_string + strlen( spec_string ) - 1;
    switch( *bounds )
    {
      /* ...identifying it as...
       */
      case '=':
        /*
         * ...an equality requirement...
         */
        condition = eq_key;
        ++bounds;
        break;

      case '<':
        if( *++bounds == '=' )
        {
          /* ...less than or equal
           * (<=; inclusive upper bound)...
           */
          condition = le_key;
          ++bounds;
        }
        else
          /* ...less than (exclusive upper bound)...
           */
          condition = lt_key;
        break;

      case '>':
        if( *++bounds == '=' )
        {
          /* ...greater than or equal
           * (>=; inclusive lower bound)...
           */
          condition = ge_key;
          ++bounds;
        }
        else
          /* ...or greater than (exclusive lower bound).
           */
          condition = gt_key;
        break;
    }
    do { /* Accumulate characters into the local copy of the specification,
          * until we encounter the end of the user specified string, or the
          * start of a second specification, (e.g. the second limit for a
          * version number range specification).
          */
         *++p = ((*bounds == '<') || (*bounds == '=') || (*bounds == '>'))
           ? '\0' : *bounds;
         if( *p ) ++bounds;
       } while( *p );

    /* Append an arbitrary component classification of "y", and an archive
     * type of "z", because "pkginfo" requires them, then interpret as a
     * "pkginfo" data structure...
     */
    strcpy( p, "-y.z" );
    pkgSpecs usrspec( spec_string );

    /* ...then extract the version fields of interest, and insert them
     * into the actual working reference specification...
     */
    refspec.SetPackageVersion( usrspec.GetPackageVersion() );
    refspec.SetPackageBuild( usrspec.GetPackageBuild() );
    if( (refname = usrspec.GetSubSystemVersion()) != NULL )
    {
      /* ...including the subsystem version, if any, which the user may
       * have specified...
       */
      refspec.SetSubSystemVersion( refname );
      refspec.SetSubSystemBuild( usrspec.GetSubSystemBuild() );
    }
    else
      /* ...or allowing a wild-card match otherwise.
       */
      refspec.SetSubSystemVersion( "*" );

    /* Convert the reference specification to "tarname" format...
     */
    if( (refname = refspec.GetTarName()) != NULL )
    {
      /* ...and construct a temporary "requires" specification from it.
       */
      pkgXmlNode requisite( requires_key );
      requisite.SetAttribute( condition, refname );

      /* Set the action item requirements to honour this...
       */
      SetRequirements( &requisite, &refspec );

      /* ...then release the heap memory used to temporarily store the
       * "tarname" attribute for this; (the remaining data associated
       * with this wil be automatically discarded, when the temporary
       * specification goes out of scope).
       */
      free( (void *)(refname) );
    }
  }
}

static void dmh_notify_no_match
( const char *name, pkgXmlNode *package, const char *bounds )
{
  /* Diagnostic helper, called when the user has requested a specific
   * package version for which there is no exactly matching release.
   */
  dmh_control( DMH_BEGIN_DIGEST );
  dmh_notify( DMH_ERROR, "there is no release matching %s%s\n",
      name, (bounds == NULL) ? "" : bounds
    );
  if( (package = package->FindFirstAssociate( release_key )) != NULL )
  {
    /* To assist the user in formalising a more appropriate
     * version specification...
     */
    dmh_notify( DMH_ERROR, "available candidate releases are...\n" );
    while( package )
    {
      /* ...display a list of available release tarballs...
       */
      const char *tarname = package->GetPropVal( tarname_key, NULL );
      if( tarname != NULL )
        dmh_notify( DMH_ERROR, " %s\n", tarname );

      /* ...cycling, until all have been identified.
       */
      package = package->FindNextAssociate( release_key );
    }
  }
  dmh_control( DMH_END_DIGEST );
}

void pkgXmlDocument::Schedule( unsigned long action, const char* name )
{
  /* Task scheduler interface; schedules actions to process all
   * dependencies for the package specified by "name", honouring
   * any appended version bounds specified for the parent.
   */
  char scratch_pad[strlen( name )];
  const char *bounds_specification = get_version_bounds( name );
  if( bounds_specification != NULL )
  {
    /* Separate any version bounds specification from
     * the original package name specification.
     */
    size_t scratch_pad_len = bounds_specification - name;
    name = (const char *)(memcpy( scratch_pad, name, scratch_pad_len ));
    scratch_pad[scratch_pad_len] = '\0';
  }

  pkgXmlNode *release;
  if( (release = FindPackageByName( name )) != NULL )
  {
    /* We found the specification for the named package...
     */
    pkgXmlNode *component = release->FindFirstAssociate( component_key );
    if( component != NULL )
      /*
       * When it is subdivided into component-packages,
       * we need to consider each as a possible candidate
       * for task scheduling.
       */
      release = component;

    while( release != NULL )
    {
      /* Within each candidate package or component-package...
       */
      pkgXmlNode *package = release;
      if( (release = release->FindFirstAssociate( release_key )) != NULL )
      {
        /* ...initially assume it is not installed, and that
         * no installable upgrade is available.
         */
        pkgActionItem latest;
        pkgXmlNode *installed = NULL, *upgrade = NULL;

        /* Establish the action for which dependency resolution is
         * to be performed; note that this may be promoted to a more
         * inclusive class, during resolution, so we need to reset
         * it for each new dependency which may be encountered.
         */
        request = action;

        /* Any action request processed here is, by definition,
         * a request for a primary action; mark it as such.
         */
        action |= ACTION_PRIMARY;

        /* When the user has given a version bounds specification,
         * then we must assign appropriate action item requirements.
         */
        if( bounds_specification != NULL )
          latest.ApplyBounds( release, bounds_specification );

        /* For each candidate release in turn...
         */
        while( release != NULL )
        {
          /* ...inspect it to identify any which is already installed,
           * and also the latest available...
           */
          if( is_installed( release ) )
            /*
             * ...i.e. here we have identified a release
             * which is currently installed...
             */
            latest.SelectPackage( installed = release, to_remove );

          if( latest.SelectIfMostRecentFit( release ) == release )
            /*
             * ...while this is the most recent we have
             * encountered so far.
             */
            upgrade = release;

          /* Continue with the next specified release, if any.
           */
          release = release->FindNextAssociate( release_key );
        }

        if( (installed = assert_installed( upgrade, installed )) == NULL )
        {
          /* There is no installed version...
           * therefore, there is nothing to do for any action
           * other than ACTION_INSTALL...
           */
          if( (action & ACTION_MASK) == ACTION_INSTALL )
          {
            /*
             * ...in which case, we must recursively resolve
             * any dependencies for the scheduled "upgrade".
             */
            if( latest.Selection() == NULL )
              dmh_notify_no_match( name, package, bounds_specification );
            else
              ResolveDependencies(
                  upgrade, Schedule( with_download( action ), latest )
                );
          }
          else
          { /* attempting ACTION_UPGRADE or ACTION_REMOVE
             * is an error; diagnose it.
             */
            if( component == NULL )
              /*
               * In this case, the user explicitly specified a single
               * package component, so it's a simple error...
               */
              dmh_notify( DMH_ERROR, "%s %s: package is not installed\n",
                  action_name( action & ACTION_MASK ), name
                );
            else
            {
              /* ...but here, the user specified only the package name,
               * which implicitly applies to all associated components;
               * since some may be installed, prefer to issue a warning
               * in respect of any which aren't.
               */
              const char *extname = component->GetPropVal( class_key, "" );
              char full_package_name[2 + strlen( name ) + strlen( extname )];
              sprintf( full_package_name, *extname ? "%s-%s" : "%s", name, extname );

              dmh_control( DMH_BEGIN_DIGEST );
              dmh_notify( DMH_WARNING, "%s %s: request ignored...\n",
                  extname = action_name( action & ACTION_MASK ), full_package_name
                );
              dmh_notify( DMH_WARNING, "%s: package was not previously installed\n",
                  full_package_name
                );
              dmh_notify( DMH_WARNING, "%s: it will remain this way until you...\n",
                  full_package_name
                );
              dmh_notify( DMH_WARNING, "use 'mingw-get install %s' to install it\n",
                  full_package_name
                );
              dmh_control( DMH_END_DIGEST );
            }
          }
        }
        else if( upgrade && (upgrade != installed) )
        {
          /* There is an installed version, but an upgrade to a newer
           * version is available; when performing ACTION_UPGRADE...
           */
          if( (action & ACTION_MASK) == ACTION_UPGRADE )
            /*
             * ...we must recursively resolve any dependencies...
             */
            ResolveDependencies( upgrade,
                Schedule( with_download( action ), latest )
              );

          else if( (action & ACTION_MASK) == ACTION_REMOVE )
          {
            /* ...while for ACTION_REMOVE, we have little to do,
             * beyond scheduling the removal; (we don't extend the
             * scope of a remove request to prerequisite packages,
             * so there is no need to resolve dependencies)...
             */
            latest.SelectPackage( installed );
            Schedule( action, latest );
          }
          else
          { /* ...but, we decline to proceed with ACTION_INSTALL
             * unless the --reinstall option is enabled...
             */
            if( pkgOptions()->Test( OPTION_REINSTALL ) )
            {
              /* ...in which case, we resolve dependencies for,
               * and reschedule a reinstallation of the currently
               * installed version...
               */
              latest.SelectPackage( installed );
              ResolveDependencies( installed,
                  Schedule( with_download( action | ACTION_REMOVE ), latest )
                );
            }
            else
            { /* ...otherwise, we reformulate the appropriate
               * fully qualified package name...
               */
              const char *extname = ( component != NULL )
                ? component->GetPropVal( class_key, "" )
                : "";
              char full_package_name[2 + strlen( name ) + strlen( extname )];
              sprintf( full_package_name, *extname ? "%s-%s" : "%s", name, extname );
              /*
               * ...which we then incorporate into an advisory
               * diagnostic message, which serves both to inform
               * the user of this error condition, and also to
               * suggest appropriate corrective action.
               */
              dmh_control( DMH_BEGIN_DIGEST );
              dmh_notify( DMH_ERROR, "%s: package is already installed\n",
                  full_package_name
                );
              dmh_notify( DMH_ERROR, "use 'mingw-get upgrade %s' to upgrade it\n",
                  full_package_name
                );
              dmh_notify( DMH_ERROR, "or 'mingw-get install --reinstall %s'\n",
                  full_package_name
                );
              dmh_notify( DMH_ERROR, "to reinstall the currently installed version\n" 
                );
              dmh_control( DMH_END_DIGEST );
            }
          }
        }
        else
        { /* In this case, the package is already installed,
           * and no more recent release is available; we still
           * recursively resolve its dependencies, to capture
           * any potential upgrades for them.
           */
          if( latest.Selection() == NULL )
            dmh_notify_no_match( name, package, bounds_specification );
          else
            ResolveDependencies( upgrade, Schedule( action, latest ));
        }
      }

      if( (component = component->FindNextAssociate( component_key )) != NULL )
        /*
         * When evaluating a component-package, we extend our
         * evaluation, to consider for any further components of
         * the current package.
         */
        release = component;
    }
  }

  else
    /* We found no information on the requested package;
     * diagnose as a non-fatal error.
     */
    dmh_notify( DMH_ERROR, pkgMsgUnknownPackage(), name );
}

void pkgXmlDocument::RescheduleInstalledPackages( unsigned long action )
{
  /* Wrapper function to retrieve the list of all installed packages,
   * passing each entry in turn to the standard task scheduler.  We
   * begin by locating the first sysroot entry in the XML database...
   */
  pkgXmlNode *sysroot = GetRoot()->FindFirstAssociate( sysroot_key );

  /* ...then, while we have sysroots to examine...
   */
  while( sysroot != NULL )
  {
    /* ...we retrieve the first package installation record within
     * the current sysroot data set.
     */
    pkgXmlNode *package = sysroot->FindFirstAssociate( installed_key );

    /* Within each sysroot, until we've retrieved all embedded
     * installation records...
     */
    while( package != NULL )
    {
      /* ...we read the canonical tarname for the package,
       * and when it is appropriately specified...
       */
      const char *tarname = package->GetPropVal( tarname_key, NULL );
      if( tarname != NULL )
      {
        /* ...we decode it, to determine the package name,
         * subsystem name and component class.
         */
        pkgSpecs decode( tarname );
        const char *pkgname = decode.GetPackageName();
        const char *sysname = decode.GetSubSystemName();
        const char *cptname = decode.GetComponentClass();

        /* From these three, we need to reconstruct an effective
         * package name for the scheduler look-up; this reconstruction
         * is performed using the following formatted buffer.
         */
        const char *fmt = "%s-%s";
        char refname[3 + strlen( sysname ) + strlen( pkgname ) + strlen( cptname )];
        if( FindPackageByName( pkgname, sysname ) == NULL )
        {
          /* The package name alone is insufficient for a successful
           * look-up; assume that the effective package name has been
           * defined by prefixing the sysroot name.
           */
          sprintf( refname, fmt, sysname, pkgname );
          pkgname = refname;
        }
        if( cptname != NULL )
        {
          /* A fully qualified logical package name should include
           * the component class name, abstracted from the canonical
           * tarname, and appended to the package name.
           */
          sprintf( refname, fmt, pkgname, cptname );
          pkgname = refname;
        }

        /* Having constructed the effective logical package name,
         * we schedule the requested action on the package...
         */
        Schedule( action, pkgname );
      }
      /* ...then move on to the next installed package, if any,
       * within the current sysroot data set...
       */
      package = package->FindNextAssociate( installed_key );
    }
    /* ...and ultimately, to the next sysroot, if any, in the
     * XML database.
     */
    sysroot = sysroot->FindNextAssociate( sysroot_key );
  }
}

/* $RCSfile$: end of file */