On Sat, Jun 1, 2024 at 3:22 PM Masahiro Yamada <masahi...@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
