Remake
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Remake, a build system that bridges the gap between make and redo.

As with make, remake uses a centralized rule file, which is named Remakefile. It contains rules with a make-like syntax:

target1 target2 ... : prerequisite1 prerequisite2 ...
        shell script
        that builds
        the targets

A target is known to be up-to-date if all its prerequisites are. If it has no known prerequisites yet the file already exits, it is assumed to be up-to-date. Obsolete targets are rebuilt thanks to the shell script provided by the rule.

As with redo, remake supports dynamic dependencies in addition to these static dependencies. Whenever a script executes remake prerequisite4 prerequisite5 ..., these prerequisites are rebuilt if they are obsolete. (So remake acts like redo-ifchange.) Moreover, all the dependencies are stored in file .remake so that they are remembered in subsequent runs. Note that dynamic dependencies from previous runs are only used to decide whether a target is obsolete; they are not automatically rebuilt when they are obsolete yet a target depends on them. They will only be rebuilt once the dynamic call to remake is executed.

In other words, the following two rules have almost the same behavior.

target1 target2 ... : prerequisite1 prerequisite2 ...
        shell script

target1 target2 ... :
        remake prerequisite1 prerequisite2 ...
        shell script

(There is a difference if the targets already exist, have never been built before, and the prerequisites are either younger or obsolete, since the targets will not be rebuilt in the second case.)

The above usage of dynamic dependencies is hardly useful. Their strength lies in the fact that they can be computed on the fly:

%.o : %.c
        gcc -MMD -MF $@.d -o $@ -c $<
        remake -r < $@.d
        rm $@.d

%.cmo : %.ml
        ocamldep $< | remake -r $@
        ocamlc -c $<

after.xml: before.xml rules.xsl
        xsltproc --load-trace -o after.xml rules.xsl before.xml 2> deps
        remake `sed -n -e "\\,//,! s,^.*URL=\"\\([^\"]*\\).*\$,\\1,p" deps`
        rm deps

Note that the first rule fails if any of the header files included by a C source file has to be automatically generated. In that case, one should perform a first call to remake them before calling the compiler. (Dependencies from several calls to remake are cumulative, so they will all be remembered the next time.)

Usage

Usage: remake options targets

Options:

Syntax

Lines starting with a space character or a tabulation are assumed to be rule scripts. They are only allowed after a rule header.

Lines starting with # are considered to be comments and are ignored. They do interrupt rule scripts though.

Any other line is either a variable definition or a rule header. If such a line ends with a backslash, the following line break is ignored and the line extends to the next one.

Variable definitions are a single name followed by equal followed by a list of names, possibly empty.

Rule headers are a nonempty list of names, followed by a colon, followed by another list of names, possibly empty. Basically, the syntax of a rule is as follows:

targets : prerequisites
        shell script

List of names are space-separated sequences of names. If a name contains a space character, it should be put into double quotes. Names can not be any of the following special characters :$(),=". Again, quotation should be used. Quotation marks can be escaped by a backslash inside quoted names.

Variables

Variables can be used to factor lists of targets or prerequisites. They are expanded as they are encountered during Remakefile parsing.

VAR2 = a
VAR1 = c d
VAR2 += $(VAR1) b
$(VAR2) e :

Variable assignments can appear instead of prerequisites inside non-generic rules with no script. They are then expanded inside the corresponding generic rule.

foo.o: CFLAGS += -DBAR

%.o : %.c
        gcc $(CFLAGS) -MMD -MF $@.d -o $@ -c $<
        remake -r < $@.d
        rm $@.d

Note: contrarily to make, variable names have to be enclosed in parentheses. For instance, $y is not a shorthand for $(y) and is left unexpanded.

Automatic variables

The following special symbols can appear inside scripts:

Note: contrarily to make, there are no corresponding variables. For instance, $^ is not a shorthand for $(^). Another difference is that $@ is always the first target, not the one that triggered the rule.

Built-in functions

remake also supports a few built-in functions inspired from make.

Order-only prerequisites

If the static prerequisites of a rule contain a pipe symbol, prerequisites on its right do not cause the targets to become obsolete if they are newer (unless they are also dynamically registered as dependencies). They are meant to be used when the targets do not directly depend on them, but the computation of their dynamic dependencies does.

%.o : %.c | parser.h
        gcc -MMD -MF $@.d -o $@ -c $<
        remake -r < $@.d
        rm $@.d

parser.c parser.h: parser.y
        yacc -d -o parser.c parser.y

Special targets

Target .PHONY marks its prerequisites as being always obsolete.

Special variables

Variable .OPTIONS is handled specially. Its content enables some features of remake that are not enabled by default.

Semantics

When are targets obsolete?

A target is obsolete:

In all the other cases, it is assumed to be up-to-date (and so are all its siblings). Note that the last rule above says "latest" and not "earliest". While it might cause some obsolete targets to go unnoticed in corner cases, it allows for the following kind of rules:

config.h stamp-config_h: config.h.in config.status
        ./config.status config.h
        touch stamp-config_h

A config.status file generally does not update header files (here config.h) if they would not change. As a consequence, if not for the stamp-config_h file above, a header would always be considered obsolete once one of its prerequisites is modified. Note that touching config.h rather than stamp-config_h would defeat the point of not updating it in the first place, since the program files would need to be rebuilt.

Once all the static prerequisites of a target have been rebuilt, remake checks whether the target still needs to be built. If it was obsolete only because its prerequisites needed to be rebuilt and none of them changed, the target is assumed to be up-to-date.

How are targets (re)built?

There are two kinds of rules. If any of the targets or prerequisites contains a % character, the rule is said to be generic. All the targets of the rule shall then contain a single % character. All the other rules are said to be specific.

A rule is said to match a given target:

When remake tries to build a given target, it looks for a specific rule that matches it. If there is one and its script is nonempty, it uses it to rebuild the target.

Otherwise, it looks for a generic rule that matches the target. If there are several matching rules, it chooses the one with the shortest pattern (and if there are several ones, the earliest one). remake then looks for specific rules that match each target of the generic rule. All the prerequisites of these specific rules are added to those of the generic rule. The script of the generic rule is used to build the target.

Example:

t%1 t2%: p1 p%2
        commands building t%1 and t2%

t2z: p4
        commands building t2z

ty1: p3

# t2x is built by the first rule (which also builds tx1) and its prerequisites are p1, px2
# t2y is built by the first rule (which also builds ty1) and its prerequisites are p1, py2, p3
# t2z is built by the second rule and its prerequisite is p4

The set of rules from Remakefile is ill-formed:

Compilation

Installing remake is needed only if Remakefile does not specify the path to the executable for its recursive calls. Thanks to its single source file, remake can be shipped inside other packages and built at configuration time.

Differences with other build systems

Differences with make:

Differences with redo:

Limitations

Links

See Also
http://cr.yp.to/redo.html for the philosophy of redo and https://github.com/apenwarr/redo for an implementation and some comprehensive documentation.

Licensing

Author
Guillaume Melquiond
Version
0.11
Date
2012-2013

Internals

The parent remake process acts as a server. The other ones have a REMAKE_SOCKET environment variable that tells them how to contact the server. They send the content of the REMAKE_JOB_ID environment variable, so that the server can associate the child targets to the jobs that spawned them. They then wait for completion and exit with the status returned by the server. This is handled by client_mode.

The server calls load_dependencies and save_dependencies to serialize dynamic dependencies from .remake. It loads Remakefile with load_rules. It then runs server_mode, which calls server_loop.

When building a target, the following sequence of events happens: