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authorLudovic Courtès <ludo@gnu.org>2020-10-19 22:22:18 +0200
committerLudovic Courtès <ludo@gnu.org>2020-10-20 01:07:46 +0200
commit5513d621e9a1523e4cda029c47ade9eff01f73e8 (patch)
treef1454fe7e4206924196531aca194622d102cc9b2
parent39befb6261a073818f709cae6273e772f22c1cf9 (diff)
doc: Add "Build Phases" section.
* doc/guix.texi (Build Phases): New section. (Build Systems): Remove 'modify-phases' example and add cross-reference to "Build Phases". (Build Utilities)[Build Phases]: Simplify intro and link to "Build Phases". (G-Expressions): Add index entries for "code staging" and add cross-reference to "Build Phases".
-rw-r--r--doc/guix.texi187
1 files changed, 169 insertions, 18 deletions
diff --git a/doc/guix.texi b/doc/guix.texi
index 36ba1dc811..f5e31c5914 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -252,6 +252,7 @@ Programming Interface
* Package Modules:: Packages from the programmer's viewpoint.
* Defining Packages:: Defining new packages.
* Build Systems:: Specifying how packages are built.
+* Build Phases:: Phases of the build process of a package.
* Build Utilities:: Helpers for your package definitions and more.
* The Store:: Manipulating the package store.
* Derivations:: Low-level interface to package derivations.
@@ -6086,6 +6087,7 @@ package definitions.
* Package Modules:: Packages from the programmer's viewpoint.
* Defining Packages:: Defining new packages.
* Build Systems:: Specifying how packages are built.
+* Build Phases:: Phases of the build process of a package.
* Build Utilities:: Helpers for your package definitions and more.
* The Store:: Manipulating the package store.
* Derivations:: Low-level interface to package derivations.
@@ -6877,16 +6879,8 @@ The build-side module @code{(guix build gnu-build-system)} defines
@code{%standard-phases} is a list of symbol/procedure pairs, where the
procedure implements the actual phase.
-The list of phases used for a particular package can be changed with the
-@code{#:phases} parameter. For instance, passing:
-
-@example
-#:phases (modify-phases %standard-phases (delete 'configure))
-@end example
-
-means that all the phases described above will be used, except the
-@code{configure} phase. @xref{Build Utilities}, for more info on
-@code{modify-phases} and build phases in general.
+@xref{Build Phases}, for more info on build phases and ways to customize
+them.
In addition, this build system ensures that the ``standard'' environment
for GNU packages is available. This includes tools such as GCC, libc,
@@ -7716,6 +7710,162 @@ with @code{build-expression->derivation} (@pxref{Derivations,
@code{build-expression->derivation}}).
@end defvr
+@node Build Phases
+@section Build Phases
+
+@cindex build phases, for packages
+Almost all package build systems implement a notion @dfn{build phases}:
+a sequence of actions that the build system executes, when you build the
+package, leading to the installed byproducts in the store. A notable
+exception is the ``bare-bones'' @code{trivial-build-system}
+(@pxref{Build Systems}).
+
+As discussed in the previous section, those build systems provide a
+standard list of phases. For @code{gnu-build-system}, the standard
+phases include an @code{unpack} phase to unpack the source code tarball,
+a @command{configure} phase to run @code{./configure}, a @code{build}
+phase to run @command{make}, and (among others) an @code{install} phase
+to run @command{make install}; @pxref{Build Systems}, for a more
+detailed view of these phases. Likewise, @code{cmake-build-system}
+inherits these phases, but its @code{configure} phase runs
+@command{cmake} instead of @command{./configure}. Other build systems,
+such as @code{python-build-system}, have a wholly different list of
+standard phases. All this code runs on the @dfn{build side}: it is
+evaluated when you actually build the package, in a dedicated build
+process spawned by the build daemon (@pxref{Invoking guix-daemon}).
+
+Build phases are represented as association lists or ``alists''
+(@pxref{Association Lists,,, guile, GNU Guile Reference Manual}) where
+each key is a symbol for the name of the phase and the associated value
+is a procedure that accepts an arbitrary number of arguments. By
+convention, those procedures receive information about the build in the
+form of @dfn{keyword parameters}, which they can use or ignore.
+
+For example, here is how @code{(guix build gnu-build-system)} defines
+@code{%standard-phases}, the variable holding its alist of build
+phases@footnote{We present a simplified view of those build phases, but
+do take a look at @code{(guix build gnu-build-system)} to see all the
+details!}:
+
+@lisp
+;; The build phases of 'gnu-build-system'.
+
+(define* (unpack #:key source #:allow-other-keys)
+ ;; Extract the source tarball.
+ (invoke "tar" "xvf" source))
+
+(define* (configure #:key outputs #:allow-other-keys)
+ ;; Run the 'configure' script. Install to output "out".
+ (let ((out (assoc-ref outputs "out")))
+ (invoke "./configure"
+ (string-append "--prefix=" out))))
+
+(define* (build #:allow-other-keys)
+ ;; Compile.
+ (invoke "make"))
+
+(define* (check #:key (test-target "check") (tests? #true)
+ #:allow-other-keys)
+ ;; Run the test suite.
+ (if tests?
+ (invoke "make" test-target)
+ (display "test suite not run\n")))
+
+(define* (install #:allow-other-keys)
+ ;; Install files to the prefix 'configure' specified.
+ (invoke "make" "install"))
+
+(define %standard-phases
+ ;; The list of standard phases (quite a few are omitted
+ ;; for brevity). Each element is a symbol/procedure pair.
+ (list (cons 'unpack unpack)
+ (cons 'configure configure)
+ (cons 'build build)
+ (cons 'check check)
+ (cons 'install install)))
+@end lisp
+
+This shows how @code{%standard-phases} is defined as a list of
+symbol/procedure pairs (@pxref{Pairs,,, guile, GNU Guile Reference
+Manual}). The first pair associates the @code{unpack} procedure with
+the @code{unpack} symbol---a name; the second pair defines the
+@code{configure} phase similarly, and so on. When building a package
+that uses @code{gnu-build-system} with its default list of phases, those
+phases are executed sequentially. You can see the name of each phase
+started and completed in the build log of packages that you build.
+
+Let's now look at the procedures themselves. Each one is defined with
+@code{define*}: @code{#:key} lists keyword parameters the procedure
+accepts, possibly with a default value, and @code{#:allow-other-keys}
+specifies that other keyword parameters are ignored (@pxref{Optional
+Arguments,,, guile, GNU Guile Reference Manual}).
+
+The @code{unpack} procedure honors the @code{source} parameter, which
+the build system uses to pass the file name of the source tarball (or
+version control checkout), and it ignores other parameters. The
+@code{configure} phase only cares about the @code{outputs} parameter, an
+alist mapping package output names to their store file name
+(@pxref{Packages with Multiple Outputs}). It extracts the file name of
+for @code{out}, the default output, and passes it to
+@command{./configure} as the installation prefix, meaning that
+@command{make install} will eventually copy all the files in that
+directory (@pxref{Configuration, configuration and makefile
+conventions,, standards, GNU Coding Standards}). @code{build} and
+@code{install} ignore all their arguments. @code{check} honors the
+@code{test-target} argument, which specifies the name of the Makefile
+target to run tests; it prints a message and skips tests when
+@code{tests?} is false.
+
+@cindex build phases, customizing
+The list of phases used for a particular package can be changed with the
+@code{#:phases} parameter of the build system. Changing the set of
+build phases boils down to building a new alist of phases based on the
+@code{%standard-phases} alist described above. This can be done with
+standard alist procedures such as @code{alist-delete} (@pxref{SRFI-1
+Association Lists,,, guile, GNU Guile Reference Manual}); however, it is
+more convenient to do so with @code{modify-phases} (@pxref{Build
+Utilities, @code{modify-phases}}).
+
+Here is an example of a package definition that removes the
+@code{configure} phase of @code{%standard-phases} and inserts a new
+phase before the @code{build} phase, called
+@code{set-prefix-in-makefile}:
+
+@example
+(define-public example
+ (package
+ (name "example")
+ ;; other fields omitted
+ (build-system gnu-build-system)
+ (arguments
+ '(#:phases (modify-phases %standard-phases
+ (delete 'configure)
+ (add-before 'build 'set-prefix-in-makefile
+ (lambda* (#:key outputs #:allow-other-keys)
+ ;; Modify the makefile so that its
+ ;; 'PREFIX' variable points to "out".
+ (let ((out (assoc-ref outputs "out")))
+ (substitute* "Makefile"
+ (("PREFIX =.*")
+ (string-append "PREFIX = "
+ out "\n")))
+ #true))))))))
+@end example
+
+The new phase that is inserted is written as an anonymous procedure,
+introduced with @code{lambda*}; it honors the @code{outputs} parameter
+we have seen before. @xref{Build Utilities}, for more about the helpers
+used by this phase, and for more examples of @code{modify-phases}.
+
+@cindex code staging
+@cindex staging, of code
+Keep in mind that build phases are code evaluated at the time the
+package is actually built. This explains why the whole
+@code{modify-phases} expression above is quoted (it comes after the
+@code{'} or apostrophe): it is @dfn{staged} for later execution.
+@xref{G-Expressions}, for an explanation of code staging and the
+@dfn{code strata} involved.
+
@node Build Utilities
@section Build Utilities
@@ -7929,13 +8079,12 @@ Return the complete file name for @var{program} as found in
@subsection Build Phases
@cindex build phases
-The @code{(guix build utils)} also contains tools to manipulate
-@dfn{build phases} as found in @code{gnu-build-system} and in fact most
-build systems (@pxref{Build Systems}). Build phases are represented as
-association lists or ``alists'' (@pxref{Association Lists,,, guile, GNU
-Guile Reference Manual}) where each key is a symbol for the name of the
-phase, and the associated value is a procedure that accepts an arbitrary
-number of arguments.
+The @code{(guix build utils)} also contains tools to manipulate build
+phases as used by build systems (@pxref{Build Systems}). Build phases
+are represented as association lists or ``alists'' (@pxref{Association
+Lists,,, guile, GNU Guile Reference Manual}) where each key is a symbol
+naming the phase and the associated value is a procedure (@pxref{Build
+Phases}).
Guile core and the @code{(srfi srfi-1)} module both provide tools to
manipulate alists. The @code{(guix build utils)} module complements
@@ -8681,6 +8830,8 @@ These build actions are performed when asking the daemon to actually
build the derivations; they are run by the daemon in a container
(@pxref{Invoking guix-daemon}).
+@cindex code staging
+@cindex staging, of code
@cindex strata of code
It should come as no surprise that we like to write these build actions
in Scheme. When we do that, we end up with two @dfn{strata} of Scheme
@@ -8692,7 +8843,7 @@ on this topic}, refers to this kind of code generation as
@dfn{staging}.}: the ``host code''---code that defines packages, talks
to the daemon, etc.---and the ``build code''---code that actually
performs build actions, such as making directories, invoking
-@command{make}, etc.
+@command{make}, and so on (@pxref{Build Phases}).
To describe a derivation and its build actions, one typically needs to
embed build code inside host code. It boils down to manipulating build