0000763: If rule has no prerequisites or commands, and target is non-existent, imagine it's been updated

ID	Project	Category	View Status	Date Submitted	Last Update

0000763	1003.1(2008)/Issue 7	Shell and Utilities	public	2013-10-10 02:18	2019-06-10 08:55

Reporter	dwheeler	Assigned To	ajosey
Priority	normal	Severity	Editorial	Type	Clarification Requested
Status	Closed	Resolution	Accepted As Marked

Name	David A. Wheeler
Organization
User Reference
Section	make
Page Number	2911
Line Number	95628-95636
Interp Status	---
Final Accepted Text	See 0000763:0001949.


Summary	0000763: If rule has no prerequisites or commands, and target is non-existent, imagine it's been updated
Description	Many people want to have "make" dependencies automatically generated. However, many tools and approaches (such as automake) that do this depend on a poorly-documented interpretation of make's specification. I'd like to see this interpretation clarified and clearly stated. As explained in "Advanced Auto-Dependency Generation" (http://mad-scientist.net/make/autodep.html), it's common to create a "dependency" file for each source file that contains the dependency statement for the target. This normally works, but it creates a serious problem when done the obvious way: "if you remove or rename a prerequisite file (say a C .h file), make will stop with a fatal error, complaining that the target doesn't exist". Tom Tromey found a solution, which appears to be the approach used by automake. IF you mention the file as a target in the makefile with no commands and no prerequisites, then if the file doesn't exist, make is supposed to silently pretend it was recreated. The same approach is recommended here: http://scottmcpeak.com/autodepend/autodepend.html (and probably many other places). This solution works in GNU make, and I suspect it works in many makes. However, this solution assumes a particular interpretation of the rules in make's "EXTENDED DESCRIPTION" that is not immediately obvious from the POSIX text (at best). I'd like to see this stated clearly, so that it can be relied on by systems that automatically generate dependencies.
Desired Action	After "If there are no commands listed for the target, the target shall be treated as up-to-date." append the following: "If a target has no prerequisites or commands, and the target of the rule is a nonexistent file, then `make' imagines this target to have been updated whenever its rule is run. This implies that all targets depending on this one will always have their commands run." (Note that this text is similar to the GNU make section 4.7 text: http://www.gnu.org/software/make/manual/html_node/Force-Targets.html).
Tags	tc2-2008

Don Cragun 2013-10-31 16:22 manager bugnote:0001949 Last edited: 2013-11-07 16:27	This issue was reopened and discussed during the November 7, 2013 conference call. This note has been updated to address the changed resolution. The standard was already clear on the requirements, but a note is being added to the application usage to serve as a hint for people who might have missed the normative requirement: Add to the end of the APPLICATION USAGE (p2922 L96124, or in the 2013 edition P2948 L97603): As a consequence of the general rules for target updating, a useful special case is that if a target has no prerequisites and no commands, and the target of the rule is a nonexistent file, then make acts as if this target has been updated whenever its rule is run. (Note: This implies that all targets depending on this one will always have their commands run.)

geoffclare 2013-11-07 09:35 manager bugnote:0001964	I'm reopening the bug, based on this input from Konrad Schwarz ... The proposed addition is: If a target has no prerequisites or commands, and the target of the rule is a nonexistent file, then make shall act as if this target has been updated whenever its rule is run. (Note: This implies that all targets depending on this one will always have their commands run.) However, make always acts if the target has been updated whenever its rule is run, irrespective of whether it has prerequisites, commands, or does or does not exist. This immediately follows from the first two paragraphs of the Extended Description: The make utility attempts to perform the actions required to ensure that the specified targets are up-to-date. A target is considered out-of-date if it is older than any of its prerequisites or if it does not exist. The make shall treat all prerequisites as targets themselves and recursively ensure that they are up-to-date, processing them in the order in which they appear in the rule. The make utility shall use the modification times of files to determine whether the corresponding targets are out-of-date. After make has ensured that all of the prerequisites of a target are up-to-date and if the target is out-of-date, the commands associated with the target entry shall be executed. If there are no commands listed for the target, the target shall be treated as up-to-date. Target does not exist -> it is out-of-date. Target has no prerequisites -> no further targets need to be examined. Target has no commands -> the target is treated as up to date. (Target is up to date -> targets depending on this one need to be updated.) The proposed addition makes it sound like non-existent targets without prerequisites or commands receive special treatment, whereas in fact they don't.

shware_systems 2013-11-07 11:45 reporter bugnote:0001965	I dunno... maybe some makes were treating "not exist" as out-of-date, and since no prerequisites weren't bothering to check if any commands or not to override the out-of-date. The language should probably be: Change: The make utility attempts to perform the actions required to ensure that the specified targets are up-to-date. A target is considered out-of-date if it is older than any of its prerequisites or if it does not exist. To: The make utility attempts to perform the actions required to ensure that the specified targets are up-to-date. An existing target file is considered out-of-date if it is older than any of its prerequisites. If it exists but does not have any prerequisites it shall be considered as up-to-date. If it does not exist, and it has no prerequisites or commands it shall also be considered up-to-date. If it does not exist and has no prerequisites but does have commands, these shall be executed and the target considered up-to-date, whether the commands create the target or not. Otherwise a file that does not exist shall also be considered out-of-date. followed by the rest of paragraph. I think that covers the intent that checking both prerequisites and commands shall be done when the file doesn't exist, and makes the Desired Action explicit. It also adds the missing case of exists but no prerequisites. Treating it as up-to-date allows create-once rules if not exist, recreate if deleted sort of thing.

Date Modified	Username	Field	Change
2013-10-10 02:18	dwheeler	New Issue
2013-10-10 02:18	dwheeler	Status	New => Under Review
2013-10-10 02:18	dwheeler	Assigned To	=> ajosey
2013-10-10 02:18	dwheeler	Name	=> David A. Wheeler
2013-10-10 02:18	dwheeler	Section	=> make
2013-10-10 02:18	dwheeler	Page Number	=> 2911
2013-10-10 02:18	dwheeler	Line Number	=> 95628-95636
2013-10-31 16:22	Don Cragun	Interp Status	=> ---
2013-10-31 16:22	Don Cragun	Note Added: 0001949
2013-10-31 16:22	Don Cragun	Status	Under Review => Resolved
2013-10-31 16:22	Don Cragun	Resolution	Open => Accepted As Marked
2013-10-31 16:23	Don Cragun	Note Edited: 0001949
2013-10-31 16:23	Don Cragun	Note Edited: 0001949
2013-10-31 16:24	Don Cragun	Final Accepted Text	=> See 0000763:0001949.
2013-10-31 16:24	Don Cragun	Tag Attached: tc2-2008
2013-11-07 09:35	geoffclare	Note Added: 0001964
2013-11-07 09:35	geoffclare	Status	Resolved => Under Review
2013-11-07 09:35	geoffclare	Resolution	Accepted As Marked => Reopened
2013-11-07 11:45	shware_systems	Note Added: 0001965
2013-11-07 16:27	Don Cragun	Note Edited: 0001949
2013-11-07 16:29	Don Cragun	Status	Under Review => Resolved
2013-11-07 16:29	Don Cragun	Resolution	Reopened => Accepted As Marked
2014-08-08 12:22	eblake	Relationship added	related to 0000857
2019-06-10 08:55	agadmin	Status	Resolved => Closed

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