Re: Multi-stem pattern rule

[Masahiro Yamada]

On Mon, Jun 3, 2024 at 3:14 AM Dmitry Goncharov <dgoncharov@users.sf.net> wrote:
>
> On Sat, Jun 1, 2024 at 3:22 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> > So, % matches a part of the file name, excluding the
> > directory path, correct?
>
> The behavior is trickier than that.
>
>
> When the target pattern carries no slash.
>
> $ ls
> a  makefile  p
> $ cat makefile
> all: a/.b.timestamp
> .%.timestamp: %.x; $(info building $@ from $<)
> $ make -rR --debug=i |tail +14 |head -4
>   Looking for an implicit rule for 'a/.b.timestamp'.
>    Trying pattern rule '.%.timestamp: %.x' with stem 'b'.
>    Trying implicit prerequisite 'a/b.x'.
>    Found 'a/b.x'.
>
>
>
> 1. make compares the target ('a/.b.timestamp') against the target pattern
> ('.%.timestamp') of a potential rule.
> 2. make calculates the stem. In the case of target 'a/.b.timestamp' and target
> pattern '.%.timestamp' the stem is 'a/b'.
> 3. make splits the stem to dirname 'a/' and basename 'b'.
> 4. make replaces '%' in the prerequisite pattern '%.x' with the
> basename part of the
> stem ('b'). Make prepends the dirname part of the stem ('a/') to the
> prerequisite and ends up with prerequisite 'a/b.x'.
> 5. make checks if file 'a/b.x' exists or can be made.
> In our case 'a/b.x' exists and therefore the rule matches.
>
> When the target pattern carries a slash, e.g. if the pattern was
> 'a/.%.timestamp', then
>
> $ ls
> a  makefile  p
> $ cat makefile
> all: a/.b.timestamp
> a/.%.timestamp: %.x; $(info building $@ from $<)
> $
> $
> $ make -rR --debug=i |tail +14 |head -4
> make: *** No rule to make target 'a/.b.timestamp', needed by 'all'.  Stop.
>   Looking for an implicit rule for 'a/.b.timestamp'.
>    Trying pattern rule 'a/.%.timestamp: %.x' with stem 'b'.
>    Trying implicit prerequisite 'b.x'.
>    Not found 'b.x'.
>
>
> 1. make compares the target ('a/.b.timestamp') against the target pattern
> ('a/.%.timestamp') of a potential rule.
> 2. make calculates the stem. In the case of target 'a/.b.timestamp' and target
> pattern 'a/.%.timestamp' the stem is 'b'.
> 3. make replaces '%' in the prerequisite pattern '%.x' with the
> stem ('b') and ends up with prerequisite 'b.x'.
> 4. make checks if file 'b.x' exists or can be made.
> In our case there is no 'b.x' and it cannot be made and therefore the rule 
> does
> not match.
>
>
> regards, Dmitry


Thanks a lot!


Perhaps, this might be worth documenting.


-- 
Best Regards
Masahiro Yamada