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diff --git a/doc/user/repositories.xml b/doc/user/repositories.xml new file mode 100644 index 0000000..7d955c3 --- /dev/null +++ b/doc/user/repositories.xml @@ -0,0 +1,595 @@ +<!-- + + Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 The SCons Foundation + + Permission is hereby granted, free of charge, to any person obtaining + a copy of this software and associated documentation files (the + "Software"), to deal in the Software without restriction, including + without limitation the rights to use, copy, modify, merge, publish, + distribute, sublicense, and/or sell copies of the Software, and to + permit persons to whom the Software is furnished to do so, subject to + the following conditions: + + The above copyright notice and this permission notice shall be included + in all copies or substantial portions of the Software. + + THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY + KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE + WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE + LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION + OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION + WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. + +--> + + <para> + + Often, a software project will have + one or more central repositories, + directory trees that contain + source code, or derived files, or both. + You can eliminate additional unnecessary + rebuilds of files by having &SCons; + use files from one or more code repositories + to build files in your local build tree. + + </para> + + <section> + <title>The &Repository; Method</title> + + <!-- + + The repository directories specified may contain source files, derived files + (objects, libraries and executables), or both. If there is no local file + (source or derived) under the directory in which Cons is executed, then the + first copy of a same-named file found under a repository directory will be + used to build any local derived files. + + --> + + <para> + + It's often useful to allow multiple programmers working + on a project to build software from + source files and/or derived files that + are stored in a centrally-accessible repository, + a directory copy of the source code tree. + (Note that this is not the sort of repository + maintained by a source code management system + like BitKeeper, CVS, or Subversion.) + <!-- + For information about using &SCons; + with these systems, see the section, + "Fetching Files From Source Code Management Systems," + below.) + --> + You use the &Repository; method + to tell &SCons; to search one or more + central code repositories (in order) + for any source files and derived files + that are not present in the local build tree: + + </para> + + <programlisting> + env = Environment() + env.Program('hello.c') + Repository('/usr/repository1', '/usr/repository2') + </programlisting> + + <para> + + Multiple calls to the &Repository; method + will simply add repositories to the global list + that &SCons; maintains, + with the exception that &SCons; will automatically eliminate + the current directory and any non-existent + directories from the list. + + </para> + + </section> + + <section> + <title>Finding source files in repositories</title> + + <para> + + The above example + specifies that &SCons; + will first search for files under + the <filename>/usr/repository1</filename> tree + and next under the <filename>/usr/repository2</filename> tree. + &SCons; expects that any files it searches + for will be found in the same position + relative to the top-level directory. + In the above example, if the &hello_c; file is not + found in the local build tree, + &SCons; will search first for + a <filename>/usr/repository1/hello.c</filename> file + and then for a <filename>/usr/repository2/hello.c</filename> file + to use in its place. + + </para> + + <para> + + So given the &SConstruct; file above, + if the &hello_c; file exists in the local + build directory, + &SCons; will rebuild the &hello; program + as normal: + + </para> + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c hello.c + cc -o hello hello.o + </screen> + + <para> + + If, however, there is no local &hello_c; file, + but one exists in <filename>/usr/repository1</filename>, + &SCons; will recompile the &hello; program + from the source file it finds in the repository: + + </para> + + + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c /usr/repository1/hello.c + cc -o hello hello.o + </screen> + + <para> + + And similarly, if there is no local &hello_c; file + and no <filename>/usr/repository1/hello.c</filename>, + but one exists in <filename>/usr/repository2</filename>: + + </para> + + + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c /usr/repository2/hello.c + cc -o hello hello.o + </screen> + + <para> + + </para> + + </section> + + <section> + <title>Finding <literal>#include</literal> files in repositories</title> + + <para> + + We've already seen that SCons will scan the contents of + a source file for <literal>#include</literal> file names + and realize that targets built from that source file + also depend on the <literal>#include</literal> file(s). + For each directory in the &cv-link-CPPPATH; list, + &SCons; will actually search the corresponding directories + in any repository trees and establish the + correct dependencies on any + <literal>#include</literal> files that it finds + in repository directory. + + </para> + + <para> + + Unless the C compiler also knows about these directories + in the repository trees, though, + it will be unable to find the <literal>#include</literal> files. + If, for example, the &hello_c; file in + our previous example includes the &hello;.h; + in its current directory, + and the &hello;.h; only exists in the repository: + + </para> + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c hello.c + hello.c:1: hello.h: No such file or directory + </screen> + + <para> + + In order to inform the C compiler about the repositories, + &SCons; will add appropriate + <literal>-I</literal> flags to the compilation commands + for each directory in the &cv-CPPPATH; list. + So if we add the current directory to the + construction environment &cv-CPPPATH; like so: + + </para> + + <programlisting> + env = Environment(CPPPATH = ['.']) + env.Program('hello.c') + Repository('/usr/repository1') + </programlisting> + + <para> + + Then re-executing &SCons; yields: + + </para> + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c -I. -I/usr/repository1 hello.c + cc -o hello hello.o + </screen> + + <para> + + The order of the <literal>-I</literal> options replicates, + for the C preprocessor, + the same repository-directory search path + that &SCons; uses for its own dependency analysis. + If there are multiple repositories and multiple &cv-CPPPATH; + directories, &SCons; will add the repository directories + to the beginning of each &cv-CPPPATH; directory, + rapidly multiplying the number of <literal>-I</literal> flags. + If, for example, the &cv-CPPPATH; contains three directories + (and shorter repository path names!): + + </para> + + <programlisting> + env = Environment(CPPPATH = ['dir1', 'dir2', 'dir3']) + env.Program('hello.c') + Repository('/r1', '/r2') + </programlisting> + + <para> + + Then we'll end up with nine <literal>-I</literal> options + on the command line, + three (for each of the &cv-CPPPATH; directories) + times three (for the local directory plus the two repositories): + + </para> + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c -Idir1 -I/r1/dir1 -I/r2/dir1 -Idir2 -I/r1/dir2 -I/r2/dir2 -Idir3 -I/r1/dir3 -I/r2/dir3 hello.c + cc -o hello hello.o + </screen> + +<!-- + +Cons classic did the following, does SCons? + +In order to shorten the command lines as much as possible, Cons will +remove C<-I> flags for any directories, locally or in the repositories, +which do not actually exist. (Note that the C<-I> flags are not included +in the MD5 signature calculation for the target file, so the target will +not be recompiled if the compilation command changes due to a directory +coming into existence.) + +--> + + <section> + <title>Limitations on <literal>#include</literal> files in repositories</title> + + <para> + + &SCons; relies on the C compiler's + <literal>-I</literal> options to control the order in which + the preprocessor will search the repository directories + for <literal>#include</literal> files. + This causes a problem, however, with how the C preprocessor + handles <literal>#include</literal> lines with + the file name included in double-quotes. + + </para> + + <para> + + As we've seen, + &SCons; will compile the &hello_c; file from + the repository if it doesn't exist in + the local directory. + If, however, the &hello_c; file in the repository contains + a <literal>#include</literal> line with the file name in + double quotes: + + </para> + + <programlisting> + #include "hello.h" + int + main(int argc, char *argv[]) + { + printf(HELLO_MESSAGE); + return (0); + } + </programlisting> + + <para> + + Then the C preprocessor will <emphasis>always</emphasis> + use a &hello_h; file from the repository directory first, + even if there is a &hello_h; file in the local directory, + despite the fact that the command line specifies + <literal>-I</literal> as the first option: + + </para> + + + + <screen> + % <userinput>scons -Q</userinput> + cc -o hello.o -c -I. -I/usr/repository1 /usr/repository1/hello.c + cc -o hello hello.o + </screen> + + <para> + + This behavior of the C preprocessor--always search + for a <literal>#include</literal> file in double-quotes + first in the same directory as the source file, + and only then search the <literal>-I</literal>--can + not, in general, be changed. + In other words, it's a limitation + that must be lived with if you want to use + code repositories in this way. + There are three ways you can possibly + work around this C preprocessor behavior: + + </para> + + <orderedlist> + + <listitem> + <para> + + Some modern versions of C compilers do have an option + to disable or control this behavior. + If so, add that option to &cv-link-CFLAGS; + (or &cv-link-CXXFLAGS; or both) in your construction environment(s). + Make sure the option is used for all construction + environments that use C preprocessing! + + </para> + </listitem> + + <listitem> + <para> + + Change all occurrences of <literal>#include "file.h"</literal> + to <literal>#include <file.h></literal>. + Use of <literal>#include</literal> with angle brackets + does not have the same behavior--the <literal>-I</literal> + directories are searched first + for <literal>#include</literal> files--which + gives &SCons; direct control over the list of + directories the C preprocessor will search. + + </para> + </listitem> + + <listitem> + <para> + + Require that everyone working with compilation from + repositories check out and work on entire directories of files, + not individual files. + (If you use local wrapper scripts around + your source code control system's command, + you could add logic to enforce this restriction there. + + </para> + </listitem> + + </orderedlist> + + </section> + + </section> + + <section> + <title>Finding the &SConstruct; file in repositories</title> + + <para> + + &SCons; will also search in repositories + for the &SConstruct; file and any specified &SConscript; files. + This poses a problem, though: how can &SCons; search a + repository tree for an &SConstruct; file + if the &SConstruct; file itself contains the information + about the pathname of the repository? + To solve this problem, &SCons; allows you + to specify repository directories + on the command line using the <literal>-Y</literal> option: + + </para> + + <screen> + % <userinput>scons -Q -Y /usr/repository1 -Y /usr/repository2</userinput> + </screen> + + <para> + + When looking for source or derived files, + &SCons; will first search the repositories + specified on the command line, + and then search the repositories + specified in the &SConstruct; or &SConscript; files. + + </para> + + </section> + + <section> + <title>Finding derived files in repositories</title> + + <para> + + If a repository contains not only source files, + but also derived files (such as object files, + libraries, or executables), &SCons; will perform + its normal MD5 signature calculation to + decide if a derived file in a repository is up-to-date, + or the derived file must be rebuilt in the local build directory. + For the &SCons; signature calculation to work correctly, + a repository tree must contain the &sconsign; files + that &SCons; uses to keep track of signature information. + + </para> + + <para> + + Usually, this would be done by a build integrator + who would run &SCons; in the repository + to create all of its derived files and &sconsign; files, + or who would run &SCons; in a separate build directory + and copy the resulting tree to the desired repository: + + </para> + + + + <screen> + % <userinput>cd /usr/repository1</userinput> + % <userinput>scons -Q</userinput> + cc -o file1.o -c file1.c + cc -o file2.o -c file2.c + cc -o hello.o -c hello.c + cc -o hello hello.o file1.o file2.o + </screen> + + <para> + + (Note that this is safe even if the &SConstruct; file + lists <filename>/usr/repository1</filename> as a repository, + because &SCons; will remove the current build directory + from its repository list for that invocation.) + + </para> + + <para> + + Now, with the repository populated, + we only need to create the one local source file + we're interested in working with at the moment, + and use the <literal>-Y</literal> option to + tell &SCons; to fetch any other files it needs + from the repository: + + </para> + + <!-- + <scons_output example="ex4"> + <scons_output_command>cd $HOME/build</scons_output_command> + <scons_output_command>edit hello.c</scons_output_command> + <scons_output_command>scons -Q -Y __ROOT__/usr/repository1</scons_output_command> + </scons_output> + --> + <screen> + % <userinput>cd $HOME/build</userinput> + % <userinput>edit hello.c</userinput> + % <userinput>scons -Q -Y /usr/repository1</userinput> + cc -c -o hello.o hello.c + cc -o hello hello.o /usr/repository1/file1.o /usr/repository1/file2.o + </screen> + + <para> + + Notice that &SCons; realizes that it does not need to + rebuild local copies <filename>file1.o</filename> and <filename>file2.o</filename> files, + but instead uses the already-compiled files + from the repository. + + </para> + + </section> + + <section> + <title>Guaranteeing local copies of files</title> + + <para> + + If the repository tree contains the complete results of a build, + and we try to build from the repository + without any files in our local tree, + something moderately surprising happens: + + </para> + + <screen> + % <userinput>mkdir $HOME/build2</userinput> + % <userinput>cd $HOME/build2</userinput> + % <userinput>scons -Q -Y /usr/all/repository hello</userinput> + scons: `hello' is up-to-date. + </screen> + + <para> + + Why does &SCons; say that the &hello; program + is up-to-date when there is no &hello; program + in the local build directory? + Because the repository (not the local directory) + contains the up-to-date &hello; program, + and &SCons; correctly determines that nothing + needs to be done to rebuild that + up-to-date copy of the file. + + </para> + + <para> + + There are, however, many times when you want to ensure that a + local copy of a file always exists. + A packaging or testing script, for example, + may assume that certain generated files exist locally. + To tell &SCons; to make a copy of any up-to-date repository + file in the local build directory, + use the &Local; function: + + </para> + + <programlisting> + env = Environment() + hello = env.Program('hello.c') + Local(hello) + </programlisting> + + <para> + + If we then run the same command, + &SCons; will make a local copy of the program + from the repository copy, + and tell you that it is doing so: + + </para> + + <screen> + % <userinput>scons -Y /usr/all/repository hello</userinput> + Local copy of hello from /usr/all/repository/hello + scons: `hello' is up-to-date. + </screen> + + <para> + + (Notice that, because the act of making the local copy + is not considered a "build" of the &hello; file, + &SCons; still reports that it is up-to-date.) + + </para> + + </section> |