make.c #6

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/*
 * Copyright 1993, 1995 Christopher Seiwald.
 *
 * This file is part of Jam - see jam.c for Copyright information.
 */

/*
 * make.c - bring a target up to date, once rules are in place
 *
 * This modules controls the execution of rules to bring a target and
 * its dependencies up to date.  It is invoked after the targets, rules,
 * et. al. described in rules.h are created by the interpreting of the
 * jam files.
 *
 * This file contains the main make() entry point and the first pass
 * make0().  The second pass, make1(), which actually does the command
 * execution, is in make1.c.
 *
 * External routines:
 *	make() - make a target, given its name
 *
 * Internal routines:
 * 	make0() - bind and scan everything to make a TARGET
 * 	make0sort() - reorder TARGETS chain by their time (newest to oldest)
 *
 * 12/26/93 (seiwald) - allow NOTIME targets to be expanded via $(<), $(>)
 * 01/04/94 (seiwald) - print all targets, bounded, when tracing commands
 * 04/08/94 (seiwald) - progress report now reflects only targets with actions
 * 04/11/94 (seiwald) - Combined deps & headers into deps[2] in TARGET.
 * 12/20/94 (seiwald) - NOTIME renamed NOTFILE.
 * 12/20/94 (seiwald) - make0() headers after determining fate of target, so 
 *			that headers aren't seen as dependents on themselves.
 * 01/19/95 (seiwald) - distinguish between CANTFIND/CANTMAKE targets.
 * 02/02/95 (seiwald) - propagate leaf source time for new LEAVES rule.
 * 02/14/95 (seiwald) - NOUPDATE rule means don't update existing target.
 * 08/22/95 (seiwald) - NOUPDATE targets immune to anyhow (-a) flag.
 * 09/06/00 (seiwald) - NOCARE affects targets with sources/actions.
 * 03/02/01 (seiwald) - reverse NOCARE change.
 * 03/14/02 (seiwald) - TEMPORARY targets no longer take on parents age
 * 03/16/02 (seiwald) - support for -g (reorder builds by source time)
 */

# include "jam.h"

# include "lists.h"
# include "parse.h"
# include "variable.h"
# include "rules.h"

# include "search.h"
# include "newstr.h"
# include "make.h"
# include "headers.h"
# include "command.h"

# ifndef max
# define max( a,b ) ((a)>(b)?(a):(b))
# endif

typedef struct {
	int	temp;
	int	updating;
	int	cantfind;
	int	cantmake;
	int	targets;
	int	made;
} COUNTS ;

static void make0( TARGET *t, time_t ptime, int depth, 
		COUNTS *counts, int anyhow );

static TARGETS *make0sort( TARGETS *c );

static char *target_fate[] = 
{
	"init",		/* T_FATE_INIT */
	"making", 	/* T_FATE_MAKING */
	"stable", 	/* T_FATE_STABLE */
	"newer",	/* T_FATE_NEWER */
	"temp", 	/* T_FATE_ISTMP */
	"touched", 	/* T_FATE_TOUCHED */
	"missing", 	/* T_FATE_MISSING */
	"old", 		/* T_FATE_OUTDATED */
	"update", 	/* T_FATE_UPDATE */
	"nofind", 	/* T_FATE_CANTFIND */
	"nomake" 	/* T_FATE_CANTMAKE */
} ;

static char *target_bind[] = 
{
	"unbound",
	"missing",
	"parents",
	"exists",
} ;

# define spaces(x) ( "                " + 16 - ( x > 16 ? 16 : x ) )

/*
 * make() - make a target, given its name
 */

int
make( 
	int	n_targets,
	char	**targets,
	int	anyhow )
{
	int i;
	COUNTS counts[1];
	int status = 0;		/* 1 if anything fails */

	memset( (char *)counts, 0, sizeof( *counts ) );

	for( i = 0; i < n_targets; i++ )
	{
	    TARGET *t = bindtarget( targets[i] );

	    make0( t, (time_t)0, 0, counts, anyhow );
	}

	if( DEBUG_MAKE )
	{
	    if( counts->targets )
		printf( "...found %d target(s)...\n", counts->targets );
	    if( counts->temp )
		printf( "...using %d temp target(s)...\n", counts->temp );
	    if( counts->updating )
		printf( "...updating %d target(s)...\n", counts->updating );
	    if( counts->cantfind )
		printf( "...can't find %d target(s)...\n", counts->cantfind );
	    if( counts->cantmake )
		printf( "...can't make %d target(s)...\n", counts->cantmake );
	}

	status = counts->cantfind || counts->cantmake;

	for( i = 0; i < n_targets; i++ )
	    status |= make1( bindtarget( targets[i] ) );

	return status;
}

/*
 * make0() - bind and scan everything to make a TARGET
 *
 * Make0() recursively binds a target, searches for #included headers,
 * calls itself on those headers, and calls itself on any dependents.
 */

static void
make0( 
	TARGET	*t,
	time_t	ptime,		/* parent target's timestamp */
	int	depth,		/* for display purposes */
	COUNTS	*counts,	/* for reporting */
	int	anyhow )	/* forcibly touch all (real) targets */
{
	TARGETS	*c;
	int	fate, hfate;
	time_t	last, leaf, hlast, hleaf;
	char	*flag = "";

	if( DEBUG_MAKEPROG )
	    printf( "make\t--\t%s%s\n", spaces( depth ), t->name );

	/* 
	 * Step 1: don't remake if already trying or tried 
	 */

	switch( t->fate )
	{
	case T_FATE_MAKING:
	    printf( "warning: %s depends on itself\n", t->name );
	    return;

	default:
	    return;

	case T_FATE_INIT:
	    break;
	}

	t->fate = T_FATE_MAKING;

	/*
	 * Step 2: under the influence of "on target" variables,
	 * bind the target and search for headers.
	 */

	/* Step 2a: set "on target" variables. */

	pushsettings( t->settings );

	/* Step 2b: find and timestamp the target file (if it's a file). */

	if( t->binding == T_BIND_UNBOUND && !( t->flags & T_FLAG_NOTFILE ) )
	{
	    t->boundname = search( t->name, &t->time );
	    t->binding = t->time ? T_BIND_EXISTS : T_BIND_MISSING;
	}

	/* If temp file doesn't exist but parent does, use parent */

	if( t->binding == T_BIND_MISSING && t->flags & T_FLAG_TEMP && ptime )
	    t->binding = T_BIND_PARENTS;

	/* Step 2c: If its a file, search for headers. */

	if( t->binding == T_BIND_EXISTS )
	    headers( t );

	/* Step 2d: reset "on target" variables */

	popsettings( t->settings );

	/* 
	 * Pause for a little progress reporting 
	 */

	if( DEBUG_BIND )
	{
	    if( strcmp( t->name, t->boundname ) )
	    {
		printf( "bind\t--\t%s%s: %s\n",
			spaces( depth ), t->name, t->boundname );
	    }

	    switch( t->binding )
	    {
	    case T_BIND_UNBOUND:
	    case T_BIND_MISSING:
	    case T_BIND_PARENTS:
		printf( "time\t--\t%s%s: %s\n",
			spaces( depth ), t->name, target_bind[ t->binding ] );
		break;

	    case T_BIND_EXISTS:
		printf( "time\t--\t%s%s: %s",
			spaces( depth ), t->name, ctime( &t->time ) );
		break;
	    }
	}

	/* 
	 * Step 3: recursively make0() dependents 
	 */

	last = 0;
	leaf = 0;
	fate = T_FATE_STABLE;

	for( c = t->deps[ T_DEPS_DEPENDS ]; c; c = c->next )
	{
	    /* Pass our time or our parent's time down. */

	    int time = t->binding == T_BIND_PARENTS ? ptime : t->time;

	    make0( c->target, time, depth + 1, counts, anyhow );
	    leaf = max( leaf, c->target->leaf );
	    leaf = max( leaf, c->target->hleaf );

	    /* If LEAVES has been applied, we only heed the timestamps of */
	    /* the leaf source nodes. */

	    if( t->flags & T_FLAG_LEAVES )
	    {
		last = leaf;
		continue;
	    }

	    last = max( last, c->target->time );
	    last = max( last, c->target->htime );
	    fate = max( fate, c->target->fate );
	    fate = max( fate, c->target->hfate );
	}

	/* If a NOUPDATE file exists, make dependents eternally old. */

	if( t->flags & T_FLAG_NOUPDATE )
	{
	    last = 0;
	    t->time = 0;

	    /*
	     * Don't inherit our fate from our dependents.  Decide fate
	     * based only upon other flags and our binding (done later).
	     */

	    fate = T_FATE_STABLE;
	}

	/* Step 3b: determine fate: rebuild target or what? */

	/* 
	    In English:
		If can't find or make child, can't make target.
		If children changed, make target.
		If target missing, make it.
		If children newer, make target.
		If temp's children newer than parent, make temp.
		If deliberately touched, make it.
		If up-to-date temp file present, use it.
		If target newer than parent, mark target newer.
		Don't propagate child's "newer" status.
	*/

	if( fate >= T_FATE_BROKEN )
	{
	    fate = T_FATE_CANTMAKE;
	}
	else if( fate >= T_FATE_SPOIL )
	{
	    fate = T_FATE_UPDATE;
	}
	else if( t->binding == T_BIND_MISSING )
	{
	    fate = T_FATE_MISSING;
	}
	else if( t->binding == T_BIND_EXISTS && last > t->time )
	{
	    fate = T_FATE_OUTDATED;
	}
	else if( t->binding == T_BIND_PARENTS && last > ptime )
	{
	    fate = T_FATE_OUTDATED;
	}
	else if( t->flags & T_FLAG_TOUCHED )
	{
	    fate = T_FATE_TOUCHED;
	}
	else if( anyhow && !( t->flags & T_FLAG_NOUPDATE ) )
	{
	    fate = T_FATE_TOUCHED;
	}
	else if( t->binding == T_BIND_EXISTS && t->flags & T_FLAG_TEMP )
	{
	    fate = T_FATE_ISTMP;
	}
	else if( t->binding == T_BIND_EXISTS && t->time > ptime )
	{
	    fate = T_FATE_NEWER;
	}
	else if( fate == T_FATE_NEWER )
	{
	    fate = T_FATE_STABLE;
	}

	/* Step 3c: handle missing files */
	/* If it's missing and there are no actions to create it, boom. */
	/* If we can't make a target we don't care about, 'sokay */
	/* We could insist that there are updating actions for all missing */
	/* files, but if they have dependents we just pretend it's NOTFILE. */

	if( fate == T_FATE_MISSING && 
		!t->actions && 
		!t->deps[ T_DEPS_DEPENDS ] )
	{
	    if( t->flags & T_FLAG_NOCARE )
	    {
		fate = T_FATE_STABLE;
	    }
	    else
	    {
		printf( "don't know how to make %s\n", t->name );

		fate = T_FATE_CANTFIND;
	    }
	}

	/* Step 3d: propagate dependents' time & fate. */
	/* Set leaf time to be our time only if this is a leaf. */

	t->time = max( t->time, last );
	t->leaf = leaf ? leaf : t->time ;
	t->fate = fate;

	/* Step 3e: sort dependents by their update time. */

	if( globs.newestfirst )
	    t->deps[ T_DEPS_DEPENDS ] = make0sort( t->deps[ T_DEPS_DEPENDS ] );

	/*
	 * Step 4: Recursively make0() headers.
	 */

	/* Step 4a: recursively make0() headers */

	hlast = 0;
	hleaf = 0;
	hfate = T_FATE_STABLE;

	for( c = t->deps[ T_DEPS_INCLUDES ]; c; c = c->next )
	{
	    make0( c->target, ptime, depth + 1, counts, anyhow );
	    hlast = max( hlast, c->target->time );
	    hlast = max( hlast, c->target->htime );
	    hleaf = max( hleaf, c->target->leaf );
	    hleaf = max( hleaf, c->target->hleaf );
	    hfate = max( hfate, c->target->fate );
	    hfate = max( hfate, c->target->hfate );
	}

	/* Step 4b: propagate dependents' time & fate. */

	t->htime = hlast;
	t->hleaf = hleaf ? hleaf : t->htime;
	t->hfate = hfate;

	/* 
	 * Step 5: a little harmless tabulating for tracing purposes 
	 */

	if( !( ++counts->targets % 1000 ) && DEBUG_MAKE )
	    printf( "...patience...\n" );

	if( fate == T_FATE_ISTMP )
	    counts->temp++;
	else if( fate == T_FATE_CANTFIND )
	    counts->cantfind++;
	else if( fate == T_FATE_CANTMAKE && t->actions )
	    counts->cantmake++;
	else if( fate >= T_FATE_BUILD && fate < T_FATE_BROKEN && t->actions )
	    counts->updating++;

	if( !( t->flags & T_FLAG_NOTFILE ) && fate >= T_FATE_SPOIL )
	    flag = "+";
	else if( t->binding == T_BIND_EXISTS && ptime && t->time > ptime )
	    flag = "*";

	if( DEBUG_MAKEPROG )
	    printf( "made%s\t%s\t%s%s\n", 
		flag, target_fate[ t->fate ], 
		spaces( depth ), t->name );
}

/*
 * make0sort() - reorder TARGETS chain by their time (newest to oldest)
 */

static TARGETS *
make0sort( TARGETS *chain )
{
	TARGETS *result = 0;

	/* We walk chain, taking each item and inserting it on the */
	/* sorted result, with newest items at the front.  This involves */
	/* updating each TARGETS' c->next and c->tail.  Note that we */
	/* make c->tail a valid prev pointer for every entry.  Normally, */
	/* it is only valid at the head, where prev == tail.  Note also */
	/* that while tail is a loop, next ends at the end of the chain. */

	/* Walk current target list */

	while( chain )
	{
	    TARGETS *c = chain;
	    TARGETS *s = result;

	    chain = chain->next;

	    /* Find point s in result for c */

	    while( s && s->target->time > c->target->time )
		s = s->next;

	    /* Insert c in front of s (might be 0). */
	    /* Don't even think of deciphering this. */

	    c->next = s;			/* good even if s = 0 */
	    if( result == s ) result = c;	/* new head of chain? */
	    if( !s ) s = result;		/* wrap to ensure a next */
	    if( result != c ) s->tail->next = c; /* not head? be prev's next */
	    c->tail = s->tail;			/* take on next's prev */
	    s->tail = c;			/* make next's prev us */
	}

	return result;
}
# Change User Description Committed
#21 9951 Perforce staff jam -j now builds all command line arguments concurrently,
rather than doing one at a time.  From Craig Allsop.

New functionality documented in RELNOTES.


p4transfer.py: Transferred from production
#20 9950 Perforce staff Jam's message "warning: foo depends on itself" now uses the
current target name (t->name) rather than the target it is
considering recursing towards (c->target->name).  This just gets
the end of the loop rather than the beginning, which in the
tricky case of loops caused by HdrRule's include file scanning,
can be more accurate. 

User visible change documented in RELNOTES.


p4transfer.py: Transferred from production
#19 3057 rmg Fix mysterious rebuild problem:  in an attempt to make 'jam -dc'
output report headers updates more accurately, internal (header
collection) targets were being bound as T_BIND_PARENTS so that 
they could carry the timestamp of the actual source file.  But
that caused the fate of the internal node to be marked as 
T_FATE_NEEDTMP if anything they included was newer, and that
easily happens among header files (something is always newer 
than something else).  Now internal targets carry their parents
time, but with T_BIND_UNBOUND, like other NOTFILE targets.

Bug fix documented in RELNOTES.

=== computer:1666: Change 43415 by seiwald@play-seiwald on 2003/04/04 09:36:25
#18 2848 rmg Fix 'jam -dc' output broken by 2614.

Now the parent's timestamp is propagated to the targets marked
T_FLAG_INTERNAL, so that -dc can see that a header file is newer
than the file that includes it.

Fix to unreleased bug.

=== computer:1666: Change 40499 by seiwald@play-seiwald on 2003/01/21 22:35:27
#17 2614 rmg Fix to includes of includes not being considered, broken by 2499.

Details taken from email to jamming:

       The challenge is to make included includes appear as direct
       includes, so that they get considered.  This used to work by
       recursion, because each TARGET node computed the summary of its
       includes -- the hfate and htime -- along with the summary of
       its dependents -- the fate and time.  Alas, that previous
       arrangement confused make1() into treating headers as direct
       dependencies during the build phase.

               A.o
               |
               A.c -- A.h

               (Read depends down, includes across)
               (Failed build of A.h aborts build of A.c)

       The fix to the confused make1() problem was to consolidate the
       special handling of includes by having make0() tack onto a
       target's list of dependendies any of the target's dependents'
       includes.  Unfortunately, this fix did not recurse: if the
       target's dependents' includes included other files, those files
       were not added to the target's dependencies.

               A.o
               |
               A.c -- A.h -- B.h -- C.h

               is rewritten to:

               A.o
               |  \
               A.c A.h -- B.h -- C.h

               (A.o depends on A.h, but not B.h or C.h.  This is
               the current, broken state of jam 2.5rc1.)

       Matt's bugfix added some recursion at this point, by transitively
       appending includes' includes onto the includes chain.  But, as
       he found out (and I did before), this can slow make0() down
       considerably, as typically header files all include each other
       and you wind up with lots of really long chains.

               A.o
               |
               A.c -- A.h -- B.h -- C.h

               is rewritten to:

               A.o
               |
               A.c -- A.h -- B.h -- C.h
                    - B.h  - C.h
                    - C.h

               (Matt's fix: if the .h files include each other, the
                includes chains get very long.)

       The final(?) fix I have is relatively simple, but is an extra
       step:  to have make0() replace a target's includes chain with
       a single pseudo-target whose dependencies are the original
       target's includes.  That pseudo-target gets passed to make0(),
       which then recursively consolidates its fate and time.  This
       then makes a target's includes fate and time available in a
       single target hanging off the original target.

               A.o
               |
               A.c -- A.h -- B.h -- C.h

               is rewritten to:

               A.o
               |   \
               A.c  A.c-includes
                    |    \
                    A.h  A.h-includes
                         |    \
                         B.h  B.h-includes
                              |
                              C.h

               (New pseudo-target xxx-includes recursively consolidates
               fate and time of all included targets.)

       While this new scheme does add a node for every include file,
       it is linear, rather than exponential, and the time is pretty
       much neglible.

User-visible bugfix not documented, because there is no place
in RELNOTES for release-candidate fixes.

Bumped patchlevel to 2.5rc2.
#16 2613 rmg Fix 'actions updated' broken by 2487.

The idea was that dependents of NOTFILE targets (like "all")
shouldn't be T_FATE_NEWER (newer than their parents), but instead
left as T_FATE_STABLE.  That way the new 'jam -dc' (display
"causes") option didn't report spurious "newer" targets.  NOTFILE
targets have a 0 timestamp, making their children always look
newer, and the change was to suppress this.

But instead of checking for NOTFILE parents, the code checked
for missing parents.  And that broke 'actions updated', because
it relied on T_FATE_NEWER even if the parent was missing.

Now it checks for p->binding != T_BIND_UNBOUND (the mark of a
NOTFILE target), rather than p->binding == T_BIND_EXISTS (the
mark of an existing real target).

=== computer:1666: Change 39756 by seiwald@play-seiwald on 2003/01/03 14:53:11
#15 2529 rmg Fix "on target" variables during header scan, from Matt Armstrong.

Setting target-specific variables while under the influence of
the target's target-specific variables caused the _global_ values
to be modified.  This happened both during header file scanning
and with the "on target statement" syntax.

The manifestation of this was if a file #included itself, HdrRule
would accidentally set HDRRULE/HDRSCAN globally, and then all
files (executables, etc) would get scanned for includes.

While this borrows from Matt's fix, it is a slightly different
implementation.

User visible fix documented in RELNOTES.

=== computer:1666: Change 39095 by seiwald@play-seiwald on 2002/12/17 14:00:58
#14 2528 rmg Rewrite comments in 39049, so that there are not two 4b's.

No functional change.

=== computer:1666: Change 39076 by seiwald@play-seiwald on 2002/12/17 11:21:15
#13 2527 rmg Fix to 38399 [Public Depot 2499], which broke 35018 [2484],
which made make0() consider headers when deciding whether to
update a temporary source file.  Now we deliberately scan the
list of included headers to see if their update time is newer
than the target's parents, which can cause that target to get
built if it is a temp.

Change to unreleased behavior.

=== computer:1666: Change 39049 by seiwald@play-seiwald on 2002/12/16 21:21:04
#12 2499 rmg Fix 'includes' support so that included files aren't treated as
direct dependencies during the command execution phase.  If an
included file failed to build, make1() would bypass the including
file.

Now make0() appends each child's 'includes' onto its own 'depends'
list, eliminating 'includes'-specific code in make0() and make1().
This not only fixes the bug, but removes some complexity as well.

Bug fix documented in RELNOTES.

=== computer:1666: Change 38399 by seiwald@play-seiwald on 2002/12/03 16:00:40
#11 2493 rmg Rewrite the past: update all jam's source with comments to
reflect changes since about 2.3, very early 2001.

Whitespace only change.

=== computer:1666: Change 37660 by seiwald@play-seiwald on 2002/11/06 22:41:35

Note: I regenerated jamgram.c on my linux 7.3 system prior to
the submit, since patch was so unhappy trying to lay down the
changes from Christopher's change. Presumably this is just due to
different yacc/bison/whatever particulars on the system where
Christopher made the changes originally. - rmg
#10 2491 rmg Some consting in jam to make it more compilable by C++ compilers.

No functional change.

=== computer:1666: Change 37433 by perforce@perforce on 2002/10/30 16:08:51

Recreational const-ing of jam, for compilers that don't allow
"string" to be passed as a non-const char *.

This included a few places where we were modifying what could
possibly have been read-only storage, oddly enough.

No functional change.

=== computer:1666: Change 37602 by seiwald@play-seiwald on 2002/11/04 17:25:40
#9 2487 rmg Subtle jam adjustments in make0() to improve tracing output,
and some new tracing output (-dc: show 'causes').

First, make0() now takes a pointer p to the parent, rather
than just the parent time ptime.  This helps when setting the
T_FATE_NEWER: it's only set if the target is newer than the
parent _and the parent exists_.  Otherwise, T_FATE_NEWER gets
set for all dependenents of NOTFILE targets.

When determining fate, don't make the final check to see if we
need to downgrade T_FATE_NEWER to T_FATE_STABLE: fate is always
T_FATE_NEWER or T_FATE_STABLE, so we might as well just set it
to T_FATE_STABLE anyhow.

New -dc output shows what targets are causing things to get
rebuilt.

User visible change documented in RELNOTES.

=== computer:1666: Change 36605 by seiwald@play-seiwald on 2002/09/28 18:26:32
#8 2486 rmg Fooling around with jam's -d flag, to make it possible to specify
useful display output without turning on loads of debugging crud.

New -dd flag to display dependencies.

Provisional changes not yet documented in jam.html.

=== computer:1666: Change 36374 by seiwald@play-seiwald on 2002/09/19 15:17:20

Jam -d change: the message "...using xxx..." now only shows
up with -da, rather than in the default output.  It made it
hard to see what was happening when there were a lot of temp
files lying around.

User visible change documented in RELNOTES.

=== computer:1666: Change 36430 by seiwald@play-seiwald on 2002/09/23 11:34:12

Put jam -dx flags into 'jam -h'.

Change to undocumented behavior (jam -h's output).

=== computer:1666: Change 36551 by seiwald@play-seiwald on 2002/09/26 14:39:54

Document jam's new -d debug flags.

=== computer:1666: Change 37367 by seiwald@waffle-cyg-seiwald on 2002/10/28 16:03:46

jam -n now implies -dax, just as the old jam -n implied -d2.

Change to unreleased functionality.

=== computer:1666: Change 37550 by seiwald@waffle-cyg-seiwald on 2002/11/03 23:12:15
#7 2484 rmg Rework make0() to consider headers when deciding whether to
update a temporary source file.  This makes it possible to
have generated, temporary source files that must be regened
because an included header has been updated.

=== computer:1666: Change 35018 by seiwald@play-seiwald on 2002/07/17 10:41:35

Followon to 35018: actually update a "needtmp" target (duh).

=== computer:1666: Change 35023 by seiwald@play-seiwald on 2002/07/17 11:10:16

Fix to 35018, which handled out-of-date header files built from
temporary sources.  Unfortunately, the change made circular header
dependencies (which are legion) get reported.  Now the circular
dependency reporting is done in the call to make0() rather than at
the beginning of make0(), and step 3b (the header recursion)
simply skips that check.

Change to unreleased behavior.

=== computer:1666: Change 36247 by seiwald@waffle-cyg-seiwald on 2002/09/16 16:15:10
#6 1553 Perforce staff New -g flag to reorder targets so that they are built according
to their sources update times, rather than simply the order in
which they appear in the Jamfiles.

This flag is experimental: it isn't clear if sorting on target
time is adequate to ensure newest sources are seen first, and
it isn't clear that this is actually useful at all.

Undocumented except for a note in RELNOTES.
#5 1545 Perforce staff Handle TEMPORARY targets with multiple parents better (but not
perfectly).

Previously, a TEMPORARY target that had no timestamp of its own
(t->time == 0, due to the target being missing) took on its
parent's timestamp ptime.  The target's timestamp is used for
four things:

1. It is passed as the target's timestamp to its children,
   in case they are also TEMPORARY targets (and thus need their
   parent's timestamp).

2. It is compared against the target's children's timestamps,
   to see if the target is out of date.

3. It is compared against the target's parent time, to see if
   the target is newer than its parent (for 'actions updated').

4. It is saved as the target's timestamp, for when the target's
   parents need to see if they are out of date.

The problem was with (4) and multiple parents: the first parent's
timestamp would become the target's, which could then inadvertantly
outdate another parent older than the first but otherwise
up-to-date.

With this change a missing TEMPORARY target is left with a zero
timestamp, and the four above cases are modified for T_BIND_PARENT
targets as such:

1. The parent's timestamp is passed directly to the target's
   children.

2. The parent's timestamp is compared directly against the
   target's children's timestamps.

3. The parent's timestamp is no longer compared against the
   target's own, as it could never be older.

4. The target's timestamp remains zero (or the newest of the
   target's children's), so as not to outdate other parents.

Oddly enough, this change mostly just removes the setting of
't->time = ptime' (leaving t->time zero), and adds only a little
extra logic to use ptime directly when needed.  It also removes
the 'pbinding' parameter to make0(), as its only use (to indicate
if the parent was missing) can better be divined from !ptime.
Perfection, as they say, isn't achieved when there is nothing
more to add, but nothing more to take away.  We'll see if I
removed enough this time.

Bug fix documented in RELNOTES.
#4 556 Perforce staff Patch release jam 2.3.2: reverse NOCARE change.
 NOCARE once
again applies to targets with source and/or actions, so that
buildable header files get built.
#3 486 Perforce staff Jam 2.3.
 See RELNOTES for a list of changes from 2.2.x.

Just about every source file was touched when jam got ANSI-fied.
#2 214 Perforce staff Peter Glasscock's NOUPDATE fix, so that a missing dependency doesn't
force the update of a NOUPDATE target.  NOUPDATE targets should
only be updated if they don't exist.
#1 2 laura Add Jam/MR 2.2 source