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+# PROGRAMMING
+
+This file documents things you should know to write a new debhelper program.
+Any program with a name that begins with `dh_` should conform to these
+guidelines (with the historical exception of `dh_make`).
+
+## Standardization
+
+There are lots of debhelper commands. To make the learning curve shallower,
+I want them all to behave in a standard manner:
+
+All debhelper programs have names beginning with `dh_`. This is so we don't
+pollute the name space too much.
+
+Debhelper programs should never output anything to standard output except
+error messages, important warnings, and the actual commands they run that
+modify files under `debian/` (this last only if they are passed `-v`, and if you
+output the commands, you should indent them with 1 tab). This is so we don't
+have a lot of noise output when all the debhelper commands in a `debian/rules`
+are run, so the important stuff is clearly visible.
+
+An exception to above rule are `dh_auto_*` commands and `dh` itself. They will
+also print the commands interacting with the upstream build system and which
+of the simple debhelper programs are called. (i.e. print what a traditional
+non-[dh(1)] using `debian/rules` would print but nothing else).
+
+Debhelper programs should accept all options listed in the "SHARED
+DEBHELPER OPTIONS" section of [debhelper(7)], including any long forms of
+these options, like `--verbose`. If necessary, the options may be ignored.
+
+If debhelper commands need config files, they should use
+`debian/package.filename` as the name of the config file (replace filename
+with whatever your command wants), and `debian/filename` should also be
+checked for config information for the first binary package in
+`debian/control`. Also, debhelper commands should accept the same sort of
+information that appears in the config files, on their command lines, if
+possible, and apply that information to the first package they act on.
+The config file format should be as simple as possible, generally just a
+list of files to act on.
+
+Debhelper programs should never modify the `debian/postinst`, `debian/prerm`,
+etc scripts. Instead, they can add lines to `debian/postinst.debhelper`, etc.
+The `autoscript()` function (see below) is one easy way to do this.
+`dh_installdeb` is an exception, it will run after the other commands and
+merge these modifications into the actual postinst scripts.
+
+In general, files named `debian/*.debhelper` and all content in
+`debian/.debhelper` are internal to debhelper, and their existence or
+use should not be relied on by external programs such as the build
+process of a package. These files will be deleted by `dh_clean`.
+
+Debhelper programs should default to doing exactly what policy says to do.
+
+There are always exceptions. Just ask me.
+
+## Introducing Dh_Lib
+
+`Dh_Lib` is the library used by all debhelper programs to parse their
+arguments and set some useful variables. It's not mandatory that your
+program use `Dh_Lib.pm`, but it will make it a lot easier to keep it in sync
+with the rest of debhelper if it does, so this is highly encouraged.
+
+Use `Dh_Lib` like this:
+
+ use Debian::Debhelper::Dh_Lib;
+ our $VERSION = '1.0';
+ init();
+
+The `init()` function causes `Dh_lib` to parse the command line and do
+some other initialization tasks. If present, `$main::VERSION` will be
+used to determine the version of the tool (e.g. embedded into
+autoscript snippets).
+
+## Argument processing
+
+All debhelper programs should respond to certain arguments, such as `-v`, `-i`,
+`-a`, and `-p`. To help you make this work right, `Dh_Lib.pm` handles argument
+processing. Just call `init()`.
+
+You can add support for additional options to your command by passing an
+options hash to `init()`. The hash is then passed on the `Getopt::Long` to
+parse the command line options. For example, to add a `--foo` option, which
+sets `$dh{FOO}`:
+
+ init(options => { foo => \$dh{FOO} });
+
+After argument processing, some global variables are used to hold the
+results; programs can use them later. These variables are elements of the
+`%dh` hash.
+
+| switch | variable | description |
+|---------------------|-----------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `-v` | `VERBOSE` | should the program verbosely output what it is doing? |
+| `--no-act` | `NO_ACT` | should the program not actually do anything? |
+| `-i`,`-a`,`-p`,`-N` | `DOPACKAGES` | a space delimited list of the binary packages to act on (in `Dh_Lib.pm`, this is an array) |
+| `-i` | `DOINDEP` | set if we're acting on binary independent packages |
+| `-a` | `DOARCH` | set if we're acting on binary dependent packages |
+| `-n` | `NOSCRIPTS` | if set, do not make any modifications to the package's postinst, postrm, etc scripts. |
+| `-o` | `ONLYSCRIPTS` | if set, only make modifications to the package's scripts, but don't look for or install associated files. |
+| `-X` | `EXCLUDE` | exclude something from processing (you decide what this means for your program) (This is an array) |
+| `-X` | `EXCLUDE_FIND` | same as `EXCLUDE`, except all items are put into a string in a way that they will make find find them. (Use `!` in front to negate that, of course) Note that this should only be used inside `complex_doit()`, not in `doit()`. |
+| `-d` | `D_FLAG` | you decide what this means to your program |
+| `-P` | `TMPDIR` | package build directory (implies only one package is being acted on) |
+| `-u` | `U_PARAMS` | will be set to a string, that is typically parameters your program passes on to some other program. (This is an array) |
+| `-V` | `V_FLAG` | will be set to a string, you decide what it means to your program |
+| `-V` | `V_FLAG_SET` | will be 1 if `-V` was specified, even if no parameters were passed along with the `-V` |
+| `-A` | `PARAMS_ALL` | generally means that additional command line parameters passed to the program (other than those processed here), will apply to all binary packages the program acts on, not just the first |
+| `--mainpackage` | `MAINPACKAGE` | controls which package is treated as the main package to act on |
+| `--name` | `NAME` | a name to use for installed files, instead of the package name |
+| `--error-handler` | `ERROR_HANDLER` | a function to call on error |
+
+Any additional command line parameters that do not start with "`-`" will be
+ignored, and you can access them later just as you normally would.
+
+## Global variables
+
+The following keys are also set in the `%dh` hash when you call `init()`:
+
+- `MAINPACKAGE`
+
+ the name of the first binary package listed in `debian/control`
+
+- `FIRSTPACKAGE`
+
+ the first package we were instructed to act on. This package
+ typically gets special treatment; additional arguments
+ specified on the command line may effect it.
+
+## Functions
+
+`Dh_Lib.pm` also contains a number of functions you may find useful.
+
+- `doit([$options, ]@command)`
+
+ Pass this function an array that is a command with arguments.
+ It will run the command (unless `$dh{NO_ACT}` is set), and
+ if `$dh{VERBOSE}` is set, it will also output the command to stdout. You
+ should use this function for almost all commands your program performs
+ that manipulate files in the package build directories.
+
+ The `$options` argument (if passed) must be a hashref (added in debhelper 10.7).
+ The following key-value pairs can be used:
+
+ - `stdout` => A file name. The child process will have its STDOUT redirected
+ to that file. [debhelper (>= 10.7)]
+ - `chdir` => A directory. The child process will do a chdir into that
+ directory before executing the command. [debhelper (>= 10.9)]
+ - `update_env` => A hashref. Each key in it represents an environment variable
+ that should be set in the child (possibly replacing the existing value)
+ prior to the exec. If the value is undef, the environment variable will
+ be unset. Environment variables in `%ENV` but not listed in the `update_env`
+ hashref will be preserved as-is. [debhelper (>= 11.1)]
+
+ This will *not* invoke a shell, so meta characters will not have any special
+ meaning. Use `complex_doit` for that (or emulate via `bash -c`).
+ NB: In compat 11 and below, there was a bug that would make `doit` fork a shell
+ in one special case. This is deprecated and will be removed in compat 12.
+ The detection code for this can be disabled by passing an empty hashref for
+ as `$options`. This will make doit unconditionally avoid forking a shell.
+
+- `print_and_doit([$options, ]@command)`
+
+ Like `doit` but will print unless `$dh{QUIET}` is set. See "Standardization"
+ above for when this is allowed to be called.
+
+- `complex_doit($command)`
+
+ Pass this function a string that is a shell command, it will run it
+ similarly to how `doit()` does. You can pass more complicated commands
+ to this (i.e. commands involving piping redirection), however, you
+ have to worry about things like escaping shell metacharacters.
+
+- `verbose_print($message)`
+
+ Pass this command a string, and it will echo it if `$dh{VERBOSE}` is set.
+
+- `nonquiet_print($message)`
+
+ Pass this command a string, and it will echo it unless `$dh{QUIET}` is set.
+ See "Standardization" above for when this is allowed to be called.
+
+- `error($errormsg)`
+
+ Pass this command a string, it will output it to standard error and
+ exit.
+
+- `error_exitcode($cmd)`
+
+ Pass this subroutine a string (representing a command line), it will
+ output a message describing that the command failed to standard error
+ and exit. Note that this relies on the value of `$?` to produce a
+ meaningful error message. Even if `$?` is `0`, this *will* still terminate
+ the program (although with a rather unhelpful message).
+
+- `warning($message)`
+
+ Pass this command a string, and it will output it to standard error
+ as a warning message.
+
+- `tmpdir($dir)`
+
+ Pass this command the name of a binary package, it will return the
+ name of the tmp directory that will be used as this package's
+ package build directory. Typically, this will be `debian/package`.
+
+- `compat($num)`
+
+ Pass this command a number, and if the current compatibility level
+ is less than or equal to that number, it will return true.
+ Looks at `DH_COMPAT` to get the compatibility level.
+
+- `pkgfile($package, $basename)`
+
+ Pass this command the name of a binary package, and the base name of a
+ file, and it will return the actual filename to use. This is used
+ for allowing debhelper programs to have configuration files in the
+ `debian/` directory, so there can be one config file per binary
+ package. The convention is that the files are named
+ `debian/package.filename`, and `debian/filename` is also allowable for
+ the `$dh{MAINPACKAGE}`. If the file does not exist, nothing is returned.
+
+ If the *entire* behavior of a command, when run without any special
+ options, is determined by the existence of 1 or more pkgfiles,
+ or by the existence of a file or directory in a location in the
+ tmpdir, it can be marked as such, which allows dh to automatically
+ skip running it. Please see "Optimization techniques" below.
+
+- `pkgext($package)`
+
+ Pass this command the name of a binary package, and it will return
+ the name to prefix to files in `debian/` for this package. For the
+ `$dh{MAINPACKAGE}`, it returns nothing (there is no prefix), for the other
+ packages, it returns `package.`.
+
+- `isnative($package)`
+
+ Pass this command the name of a package, it returns 1 if the package
+ is a native debian package.
+ As a side effect, `$dh{VERSION}` is set to the version number of the
+ package.
+
+- `autoscript($package, $scriptname, $snippetname, $substparam)`
+
+ Pass parameters:
+ - binary package to be affected
+ - script to add to
+ - filename of snippet. For testing purposes, you can set the
+ environment variable `DH_DATAFILES` containing a autoscripts
+ directory, which can be used to shadow the snippets provided
+ in `/usr/share/debhelper/autoscripts` (or to test newly added
+ snippets).
+ Older versions of debhelper (<< 13.1~) do not support
+ `DH_DATAFILES`. If you need to support debhelper (<< 13.1~)
+ then you can set `DH_AUTOSCRIPTDIR` to a directory containing
+ the snippets instead (note it should point to the autoscripts
+ directory unlike `DH_DATAFILES`).
+
+ - (optional) A substitution parameter, which is one of 3 types:
+ - sed commands to run on the snippet, e.g. `s/#PACKAGE#/$PACKAGE/`.
+ Note: Passed to the shell inside double quotes.
+ - a perl sub to invoke with `$_` set to each line of the snippet
+ in turn.
+ - a hashref, where each key will substitute `#${key}#` with the
+ value that `$key` points to. [debhelper (>= 10.7)]
+
+ This command automatically adds shell script snippets to a debian
+ maintainer script (like the postinst or prerm).
+ Note that in v6 mode and up, the snippets are added in reverse
+ order for the removal scripts.
+
+- `autotrigger($package, $trigger_type, $trigger_target)`
+
+ This command automatically adds a trigger to the package. The
+ parameters:
+ - binary package to be affected
+ - the type of trigger (e.g. "activate-noawait")
+ - the target (e.g. `ldconfig` or `/usr/share/foo`)
+
+- `dirname($pathname)`
+
+ Return directory part of pathname.
+
+- `basename($pathname)`
+
+ Return base of pathname,
+
+- `addsubstvar($package, $substvar, $deppackage, $verinfo, $remove)`
+
+ This function adds a dependency on some package to the specified
+ substvar in a package's substvar's file. It needs all these
+ parameters:
+ - binary package that gets the item
+ - name of the substvar to add the item to
+ - the package that will be depended on
+ - version info for the package (optional) (i.e. ">= 1.1")
+ - if this last parameter is passed, the thing that would be added
+ is removed instead. This can be useful to ensure that a debhelper
+ command is idempotent. (However, we generally don't bother,
+ and rely on the user calling `dh_prep`.) Note that without this
+ parameter, if you call the function twice with the same values it
+ will only add one item to the substvars file.
+
+- `delsubstvar($package, $substvar)`
+
+ This function removes the entire line for the substvar from the
+ package's shlibs file.
+
+- `excludefile($filename)`
+
+ This function returns true if `-X` has been used to ask for the file
+ to be excluded.
+
+- `is_udeb($package)`
+
+ Returns true if the package is marked as a udeb in the control
+ file.
+
+- `getpackages($type)`
+
+ Returns a list of packages in the control file.
+ Pass "arch" or "indep" to specify arch-dependent or
+ -independent. If `$type` is omitted, returns all
+ packages (including packages that are not built
+ for this architecture). Pass "both" to get the union
+ of "arch" and "indep" packages.
+ Note that "both" is *not* the same omitting the `$type` parameter.
+ As a side effect, populates `%package_arches` and `%package_types` with
+ the types of all packages (not only those returned).
+
+- `get_source_date_epoch()`
+
+ Return the value of `$ENV{SOURCE_DATE_EPOCH}` if exists.
+ Otherwise compute the value from the first changelog entry,
+ use it to set the ENV variable and return it.
+
+- `inhibit_log()`
+
+ Prevent logging the program's successful finish to
+ `debian/*debhelper.log`
+
+ Since debhelper 12.9, this can be done by passing the `inhibit_log`
+ option with a value of 1 to `init()` instead. E.g.
+
+ init('inhibit_log' => 1);
+
+- `load_log($package, $hashref)`
+
+ Loads the log file for the given package and returns a list of
+ logged commands.
+ (Passing a hashref also causes it to populate the hash.)
+
+- `write_log($cmd, $package ...)`
+
+ Writes the log files for the specified package(s), adding
+ the cmd to the end.
+
+- `restore_file_on_clean($file)`
+
+ Store a copy of `$file`, which will be restored by `dh_clean`.
+ The `$file` *must* be a relative path to the package root and
+ *must* be a real regular file. Dirs, devices and symlinks
+ (and everything else) *cannot* be restored by this.
+ If `$file` is passed multiple times (e.g. from different programs)
+ only the first version is stored.
+ CAVEAT: This *cannot* undo arbitrary "rm -fr"'ing. The dir,
+ which the `$file` is/was in, must be present when `dh_clean` is
+ called.
+
+- `make_symlink($src, $dest, $tmp)`
+
+ Creates a Policy compliant system link called `$dest` pointing to
+ `$src`. If `$tmp` is given, then `$tmp` will be prefixed to `$dest`
+ when creating the actual symlink.
+
+- `install_dh_config_file($src, $dest)`
+
+ Installs `$src` into `$dest` using mode 0644.
+ If compat is 9 (or later) and `$src` is executable, `$src` will
+ be executed instead and its output will be used to generate the
+ `$dest` file.
+
+- `install_dir(@dirs)` / `mkdirs(@dirs)`
+
+ Create the directories denoted by the paths in `@dirs` and all
+ parent entries as well (as needed). It uses mode 0755.
+ If a directory listed in `@dirs` already exists, the function
+ silently skips that directory (similar to `mkdir -p`).
+
+ The `install_dir` function should be used for directories
+ installed in a final package while `mkdirs` should be used
+ for other directories. The difference is related to whether
+ the change will be shown via -v/--verbose or not. The
+ `mkdirs` function requires `debhelper (>= 13.11~)`.
+
+- `install_file($src, $dest)`
+
+ Installs `$src` into `$dest` with mode 0644. The parent dir of
+ `$dest` must exist (can be created with `install_dir`).
+ This is intended for installing regular non-executable files.
+
+- `install_prog($src, $dest)`
+
+ Installs `$src` into `$dest` with mode 0755. The parent dir of
+ `$dest` must exist (can be created with `install_dir`).
+ This is intended for installing scripts or binaries.
+
+- `install_lib($src, $dest)`
+
+ Installs a library at the path `$src` into `$dest`. The parent
+ dir of `$dest` must exist (can be created with `install_dir`).
+ This is intended for installing libraries.
+
+- `reset_perm_and_owner($mode, $path...)`
+
+ Resets the ownership and mode (POSIX permissions) of `$path`
+ This is useful for files created directly by the script, but
+ it not necessary for files installed via the `install_*`
+ functions.
+ The file owner and group is set to "root:root". The change
+ is only done on the exact paths listed (i.e. it is *not*
+ recursive).
+ Mode should be passed as an integer (not a string).
+
+- `open_gz($file)`
+
+ Open `$file`, read from it as a gzip-compressed file and return
+ the file handle.
+ Depending on runtime features, it might be a pipe from an
+ external process (which will die with a "SIGPIPE" if you
+ do not consume all the input)
+
+- `deprecated_functionality($warn_msg[, $rm_compat[, $rm_msg]])`
+
+ Emit `$warn_msg` as a deprecation warning, or error out if `$rm_compat`
+ is provided and equal to (or greater than) the active compat level.
+ The `$rm_msg` parameter can be used to provide a custom error message
+ in the latter case (if omitted, `$warn_msg` will be used in both cases).
+ The function will provide a separate diagnostic about which compat
+ level that will remove/removed the functionality if `$rm_compat` is
+ given.
+
+- `log_installed_files($package, @paths)`
+
+ Creates a logfile (in `debian/.debhelper/generated`) for the helper's
+ processing of `$package`, which installed the files listed in
+ `@paths`. This logfile will later be used by the `dh_missing` helper.
+ Paths should be relative to the package root (i.e. the directory
+ containing `debian/`) and should not have superfluous segments
+ (e.g. avoid `foo/../bar` or `foo/./bar`).
+ If a directory is listed, it and all paths recursively beneath is
+ also considered installed.
+
+- `on_pkgs_in_parallel($code)` - prototype: (&)
+
+ Short hand for `on_items_in_parallel` with `$dh{DOPACKAGES}` as
+ as list of packages.
+
+- `on_items_in_parallel($item_list_ref, $code)`
+
+ Splits all the items in `$item_list_ref` into a number of groups
+ based on the max parallel (as decided by `DEB_BUILD_OPTIONS`)
+ A subprocess is forked for each group (minimum 1 process will be
+ forked) and each subprocess will be given a group of items
+ to process. Each group is passed to the `$code` sub, which will
+ then process it and return normally on success.
+ Example:
+
+ my @all_packages = getpackages();
+ on_items_in_parallel(\@all_packages, sub {
+ for my $package (@_) {
+ my $tmp=tmpdir($package);
+ my $pkgfile = pkgfile($package, 'foo');
+ ...;
+ }
+ });
+ my @work_list = compute_work_list();
+ on_items_in_parallel(\@work_list, sub {
+ for my $item (@_) {
+ ...;
+ }
+ });
+
+ If there is an error, which should stop the build, please invoke
+ either `error()` or `error_exitcode`. Alternatively, a trappable
+ error (e.g. `die($msg)`) can also be used.
+
+ Keep in mind that the sub will always be run in a subprocess,
+ so it cannot update global state.
+
+## Sequence Addons
+
+The [dh(1)] command has a `--with <addon>` parameter that can be used to load
+a sequence addon module named `Debian::Debhelper::Sequence::<addon>`.
+These modules can add/remove commands to the dh command sequences, by
+calling some functions from `Dh_Lib`:
+
+- `insert_before($existing_command, $new_command)`
+
+ Insert `$new_command` in sequences before `$existing_command`
+
+ Compatible with "arch-only"/"indep-only" modes if the command
+ appears only in a compatible sequence.
+
+- `insert_after($existing_command, $new_command)`
+
+ Insert `$new_command` in sequences after `$existing_command`
+
+ Compatible with "arch-only"/"indep-only" modes if the command
+ appears only in a compatible sequence.
+
+- `remove_command($existing_command)`
+
+ Remove `$existing_command` from the list of commands to run
+ in all sequences.
+
+ Cannot be used in "arch-only"/"indep-only" mode.
+
+- `add_command($new_command, $sequence)`
+
+ Add `$new_command` to the beginning of the specified sequence.
+ If the sequence does not exist, it will be created.
+
+ Compatible with "arch-only"/"indep-only" modes if `$sequence`
+ is an "-arch" or "-indep" sequence (respectively).
+
+- `add_command_options($command, $opt1, $opt2, ...)`
+
+ Append `$opt1`, `$opt2` etc. to the list of additional options which
+ dh passes when running the specified `$command`. These options are
+ not relayed to debhelper commands called via `$command` override.
+
+ Cannot be used in "arch-only"/"indep-only" mode.
+
+- `remove_command_options($command)`
+
+ Clear all additional `$command` options previously added with
+ `add_command_options()`.
+
+ Cannot be used in "arch-only"/"indep-only" mode.
+
+- `remove_command_options($command, $opt1, $opt2, ...)`
+
+ Remove `$opt1`, `$opt2` etc. from the list of additional options which
+ dh passes when running the specified `$command`.
+
+ Cannot be used in "arch-only"/"indep-only" mode.
+
+- `declare_command_obsolete([$error_compat, ]$command)`
+
+ Declare `$command` as obsolete, which make dh warn about leftover
+ override / hook targets. Note that `$command` *MUST NOT* be present
+ in the sequence!
+
+ The `$error_compat` parameter defines the compat level where
+ referencing this command via a hook target will become an error.
+ This must be at least 13 (which is the default if omitted).
+ Be careful with using already closed compat levels as error compat
+ for new commands as it will cause FTBFS.
+
+ Cannot be used in "arch-only"/"indep-only" mode.
+
+## Optimization techniques
+
+Most debhelper tools will have situations where they are not useful and can
+be skipped. To support this, dh will look for a "NOOP PROMISE" as a part of
+a comment in the command before running it. These promises have the form:
+
+ # PROMISE: DH NOOP WITHOUT pkgfile-logged(pkgfileA) pkgfile-logged(pkgfileB) tmp(need/this) cli-options()
+
+The following keywords are defined:
+
+- `pkgfile(X)`: The command might do something if `debian/X` (or `debian/<package>.X`)
+ exist for any of the packages it will be run for. If the debhelper tool
+ interacts with `dh_missing`, you always want to use `pkgfile-logged(X)` instead.
+
+- `pkgfile-logged(X)`: Same as `pkgfile(X)` but it will also register which files
+ it handles so `dh_missing` can see it.
+
+- `tmp(X)`: The command might do something if `debian/<package>/X` exists.
+
+- `cli-options(--foo|--bar)`: The command might do something if *either* `--foo`
+ OR `--bar` are passed to the command.
+
+- `cli-options(BUILDSYSTEM)`: The command is a build system command (`dh_auto_*`)
+ and will react to standard build system command line options.
+
+- `cli-options()`: Special variant of `cli-options()` to declare that command
+ line options will not affect whether the tool will do something. This enables
+ dh to skip commands even when passed custom options. Without an explicit
+ `cli-option(...)` hint, dh will assume the command might react to it.
+
+If the hint is present and ALL of the keywords imply that the command can be
+skipped, dh will skip the command.
+
+## Logging helpers and dh_missing
+
+Since debhelper 10.3, debhelper has had a helper called `dh_missing`. It
+takes over the `--list-missing` and `--fail-missing` options from `dh_install`
+and as the advantage that it can "see" what other helpers have installed.
+
+Under the hood, this works by the helpers logging the source files
+they (would) install to a hidden log file. When `dh_missing` is called,
+it reads all these log files to determine which files have would been
+installed and compare them to what is present.
+
+If you are writing a helper that need to integrate with `dh_missing`,
+here is what you do:
+
+### Dh_Lib-based helpers
+
+- Replace `@{$dh{DOPACKAGES}}` with `getpackages()` and use
+ `process_pkg($package)` to determine if the helper should actually
+ install anything.
+- Call `log_installed_files` at least once per package (even on the ones
+ that are not to be acted on) with a list of source files that would be
+ installed.
+ - You can list entire directories even if there are files under
+ it that are ignored.
+ - Please call `log_installed_files` *even if* the list is empty for that
+ packages. This enables `dh_missing` to see that the helper has been run
+ and nothing should be installed for that package.
+ - Prefer calling `log_installed_files` *exactly once* per package as
+ this is what it is optimized for.
+- If your helper has a `PROMISE`, it must use `pkgfile-logged(<file>)`
+ for its config files. (See [#867246])
+ - CAVEAT: This requires a dependency on "debhelper (>= 10.2.5)". Prior
+ to that version, debhelper will wrongly optimize your helper out.
+- Consider using `dh_installman` or `dh_installexamples` as examples.
+
+### Other helpers - via dh_assistant log-installed-files
+
+This process requires debhelper/13.10 or later.
+
+- The helper must compile a list of files it would have installed for
+ each package (even packages that are not acted on). The file list
+ should be relative to the source package root (e.g.
+ `debian/tmp/usr/bin/bar`).
+ - This list can also contain directories. They will be flagged as
+ installed along with their content (recursively).
+- Invoke `dh_assistant log-installed-files --on-behalf-of-cmd=${HELPER_NAME} -p${package} ${PATHS}`
+ - Invoking `dh_assistant` when your tool has no paths to log is
+ still recommended to let dh_missing that your tool had nothing
+ to record.
+ - Prefer calling `dh_assistant log-installed-files` *exactly once*
+ per package per invocation of your tool as this is what it is
+ optimized for.
+- If your helper has a PROMISE, it must use `pkgfile-logged(<file>)`
+ for its config files (see [#867246]).
+
+### Other helpers - manually
+
+- The helper must compile a list of files it would have installed for
+ each package (even packages that are not acted on). The file list
+ should be relative to the source package root (e.g.
+ `debian/tmp/usr/bin/bar`).
+ - This list can also contain directories. They will be flagged as
+ installed along with their content (recursively).
+- The helper must append to the file (create it if missing):
+ `debian/.debhelper/generated/${package}/installed-by-${HELPER_NAME}`
+ - Example: `debian/.debhelper/generated/lintian/installed-by-dh_install`
+ - The file should be created even if it is empty. This enables `dh_missing`
+ to see that the helper has been run and nothing would be installed for
+ that package.
+- Please append to the file if it exists as the helper may be called multiple
+ times (once with `-a` and once with `-i`). It is completely fine if this
+ leaves duplicate entries as dh_missing will deduplicate these.
+- If your helper has a PROMISE, it must use `pkgfile-logged(<file>)`
+ for its config files (see [#867246]).
+ CAVEAT: This requires a dependency on "debhelper (>= 10.2.5)". Prior
+ to that version, debhelper will wrongly optimize your helper out.
+
+## Buildsystem Classes
+
+The `dh_auto_*` commands are frontends that use debhelper buildsystem
+classes. These classes have names like `Debian::Debhelper::Buildsystem::foo`,
+and are derived from `Debian::Debhelper::Buildsystem`, or other, related
+classes.
+
+A buildsystem class needs to inherit or define these methods: `DESCRIPTION`,
+`check_auto_buildable`, `configure`, `build`, `test`, `install`, `clean`. See
+the comments inside `Debian::Debhelper::Buildsystem` for details. Note that
+this interface is still subject to change.
+
+Note that third-party buildsystems will not automatically be used by
+default. The package maintainer will either have to explicitly enable
+it via the `--buildsystem` parameter OR the build system should be
+registered in debhelper. The latter is currently needed to ensure a
+stable and well-defined ordering of the build systems.
+
+[dh(1)]: https://manpages.debian.org/dh.1 "dh - debhelper command sequencer"
+[debhelper(7)]: https://manpages.debian.org/debhelper.7 "debhelper - the debhelper tool suite"
+[#867246]: https://bugs.debian.org/867246 "dh_installman incorrectly optimized away when using --fail-missing and building arch-any packages only"
+
+-- Joey Hess <joeyh@debian.org>
diff --git a/doc/README b/doc/README
new file mode 100644
index 0000000..cffbea2
--- /dev/null
+++ b/doc/README
@@ -0,0 +1 @@
+Please see the debhelper(7) man page for documentation.
diff --git a/doc/SUPPORT-POLICY b/doc/SUPPORT-POLICY
new file mode 100644
index 0000000..9463e49
--- /dev/null
+++ b/doc/SUPPORT-POLICY
@@ -0,0 +1,20 @@
+SUPPORT POLICY FOR DEBHELPER COMPAT LEVELS
+==========================================
+
+The current policy for supporting compat levels is:
+
+ * A compat level may be deprecated once the latest oldoldstable release
+ supports a /newer/ compat level. (E.g. compat 9 can be deprecated once
+ jessie becomes oldoldstable).
+
+ * Alternatively, a compat level may be deprecated if a debhelper version
+ supporting a newer compat level is backported to oldoldstable-backports/
+ oldoldstable-backports-sloppy and the oldest supported Ubuntu LTS release.
+
+ * These rules are independent of whether Debian oldoldstable is still
+ supported.
+
+ * Deprecated compat levels may be removed in unstable once it as been released
+ in Debian stable as deprecated (provided that the deprecation has been
+ announced at least one year prior to the freeze of said stable release).
+
diff --git a/doc/TODO b/doc/TODO
new file mode 100644
index 0000000..6da26db
--- /dev/null
+++ b/doc/TODO
@@ -0,0 +1,21 @@
+v10:
+
+* escaping in config files (for whitespace)?
+
+Deprecated:
+
+* dh_installmanpages.
+* dh_movefiles. I won't hold my breath. Have not added deprecation
+ docs or message yet.
+* dh_installinit --init-script (make it warn)
+* dh_clean -k
+* -s flag, not formally deprecated yet; remove eventually
+* -u flag; add a warning on use and remove eventually
+* delsubstvar() and the last parameter to addsubstvar that makes it remove
+ a string are not used in debhelper itself, but have been left in the
+ library in case other things use them. Deprecate and remove.
+* debian/compress files
+
+Also, grep the entire archive for all dh_* command lines,
+and check to see what other switches are not being used, and maybe remove
+some of them.