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.. _preprocessor:
=================
Text Preprocessor
=================
The build system contains a text preprocessor similar to the C preprocessor,
meant for processing files which have no built-in preprocessor such as XUL
and JavaScript documents. It is implemented at ``python/mozbuild/mozbuild/preprocessor.py`` and
is typically invoked via :ref:`jar_manifests`.
While used to preprocess CSS files, the directives are changed to begin with
``%`` instead of ``#`` to avoid conflict of the id selectors.
Directives
==========
Variable Definition
-------------------
define
^^^^^^
::
#define variable
#define variable value
Defines a preprocessor variable.
Note that, unlike the C preprocessor, instances of this variable later in the
source are not automatically replaced (see #filter). If value is not supplied,
it defaults to ``1``.
Note that whitespace is significant, so ``"#define foo one"`` and
``"#define foo one "`` is different (in the second case, ``foo`` is defined to
be a four-character string).
undef
^^^^^
::
#undef variable
Undefines a preprocessor variable.
Conditionals
------------
if
^^
::
#if variable
#if !variable
#if variable == string
#if variable != string
Disables output if the conditional is false. This can be nested to arbitrary
depths. Note that in the equality checks, the variable must come first.
else
^^^^
::
#else
Reverses the state of the previous conditional block; for example, if the
last ``#if`` was true (output was enabled), an ``#else`` makes it off
(output gets disabled).
endif
^^^^^
::
#endif
Ends the conditional block.
ifdef / ifndef
^^^^^^^^^^^^^^
::
#ifdef variable
#ifndef variable
An ``#if`` conditional that is true only if the preprocessor variable
variable is defined (in the case of ``ifdef``) or not defined (``ifndef``).
elif / elifdef / elifndef
^^^^^^^^^^^^^^^^^^^^^^^^^
::
#elif variable
#elif !variable
#elif variable == string
#elif variable != string
#elifdef variable
#elifndef variable
A shorthand to mean an ``#else`` combined with the relevant conditional.
The following two blocks are equivalent::
#ifdef foo
block 1
#elifdef bar
block 2
#endif
::
#ifdef foo
block 1
#else
#ifdef bar
block 2
#endif
#endif
File Inclusion
--------------
include
^^^^^^^
::
#include filename
The file specified by filename is processed as if the contents was placed
at this position. This also means that preprocessor conditionals can even
be started in one file and ended in another (but is highly discouraged).
There is no limit on depth of inclusion, or repeated inclusion of the same
file, or self inclusion; thus, care should be taken to avoid infinite loops.
includesubst
^^^^^^^^^^^^
::
#includesubst @variable@filename
Same as a ``#include`` except that all instances of variable in the included
file is also expanded as in ``#filter`` substitution
expand
^^^^^^
::
#expand string
All variables wrapped in ``__`` are replaced with their value, for this line
only. If the variable is not defined, it expands to an empty string. For
example, if ``foo`` has the value ``bar``, and ``baz`` is not defined, then::
#expand This <__foo__> <__baz__> gets expanded
Is expanded to::
This <bar> <> gets expanded
filter / unfilter
^^^^^^^^^^^^^^^^^
::
#filter filter1 filter2 ... filterN
#unfilter filter1 filter2 ... filterN
``#filter`` turns on the given filter.
Filters are run in alphabetical order on a per-line basis.
``#unfilter`` turns off the given filter. Available filters are:
emptyLines
strips blank lines from the output
dumbComments
dumbComments: empties out any line that consists of optional whitespace
followed by a ``//``. Good for getting rid of comments that are on their
own lines, and being smarter with a simple regexp filter is impossible
substitution
all variables wrapped in @ are replaced with their value. If the
variable is not defined, it is a fatal error. Similar to ``#expand``
and ``#filter``
attemptSubstitution
all variables wrapped in ``@`` are replaced with their value, or an
empty string if the variable is not defined. Similar to ``#expand``.
literal
^^^^^^^
::
#literal string
Output the string (i.e. the rest of the line) literally, with no other fixups.
This is useful to output lines starting with ``#``, or to temporarily
disable filters.
Other
-----
#error
^^^^^^
::
#error string
Cause a fatal error at this point, with the error message being the
given string.
|
