115 lines
3 KiB
Plaintext
115 lines
3 KiB
Plaintext
# (A)
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.KEEP_STATE:
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all: hello
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clean:
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rm foo.x foo.y
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foo.x:
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touch foo.x
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# <- workaround: disable command dependencies
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# ?touch foo.x
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foo.y: foo.x
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cat foo.x foo.x > foo.y
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# <- workaround: disable command dependencies
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# ?cat foo.x foo.x > foo.y
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# (B)
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include foo.y
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hello:
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echo hello
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# The perhaps unintuitive effect of `.KEEP_STATE`
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# on the generation of include files.
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#
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# Effects:
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#
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# 1) comment out the line after (A)
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#
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# $ somake -f empty_cmd.mf clean
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# rm foo.x foo.y
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# $ rm .make.state
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# $ somake -f empty_cmd.mf
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# touch foo.x
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# cat foo.x foo.x > foo.y
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# echo hello
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# hello
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# $ somake -f empty_cmd.mf
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# echo hello
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# hello
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#
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# -> meaning that the include file foo.y is only updated
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# if it doesn't exist or foo.x is newer. This is
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# the expected behavior.
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#
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# 2) comment in (A) and comment out (B)
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#
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# $ somake -f empty_cmd.mf clean
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# rm foo.x foo.y
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# $ rm .make.state
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# $ somake -f empty_cmd.mf foo.y
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# touch foo.x
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# cat foo.x foo.x > foo.y
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# $ somake -f empty_cmd.mf foo.y
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# `foo.y' is up to date.
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#
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# -> again, as expected the foo.y action is only executed once.
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#
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# 3) comment in (A) and (B)
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#
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# $ somake -f empty_cmd.mf clean
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# touch foo.x
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# cat foo.x foo.x > foo.y
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# rm foo.x foo.y
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# $ rm .make.state
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# $ somake -f empty_cmd.mf
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# touch foo.x
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# cat foo.x foo.x > foo.y
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# echo hello
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# hello
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# $ somake -f empty_cmd.mf
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# touch foo.x
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# cat foo.x foo.x > foo.y
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# echo hello
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# hello
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#
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# -> this is unexpected because foo.y is generated each time.
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# This is caused by an interaction between KEEP_STATE and
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# include. Make reads in the `.make.state` file after
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# include directives are being processed. But, as part of the
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# dependency checking of the include files the usual KEEP_STATE
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# logic is applied such that make assumes that the foo.y action
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# command changed from '' (empty) to 'cat foo.x foo.x > foo.y'.
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#
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# (make basically looks up the 'old' command in an empty database)
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#
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# When calling make with `-d` the log contains messages like:
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#
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# different from empty old command
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# Building foo.x because new command longer than old
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# Building foo.y because new command longer than old
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#
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# A workaround is to disable command dependencies for the involved
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# actions, i.e. `?touch foo` and `?cat foo.x foo.x > foo.y`
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#
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# This is a bug.
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#
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# Possible fix:
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# i) Just don't use the make.state database before it is loaded.
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# This effectively would disable command dependencies for
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# generated include files. Similar effect as the described
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# workaround.
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# ii) or, preferably, load the make.state file before any
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# processing of include directives. This would have
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# the advantage that an include file is regenerated if a
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# variable that is used in the generate action has
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# changed (think: `generate.sh $(CC) $(LD) > tool_dependent.mf`
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