mirror of
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0f7f399e93
This commit does the following.
- Renames `slashslash` as `dumbComments`. As a result, it now comes before
`emptyLines` in alphabetical ordering, which means that if you apply both
`dumbComments` and `emptyLines`, lines that contain only comments will be
fully removed.
(I contemplated changing the filter ordering to match the order specified,
rather than using alphabetical ordering, but that was more invasive and not
obviously better.)
- Changes `dumbComments` so it only applies if the comment is at the start of
the line (with optional leading whitespace). This is so it can be used with
prefs files, which contain lines like `pref("foo", "https://mozilla.org");`
where the `//` must not be treated as a comment.
Note that `slashslash` wasn't being used anywhere.
Depends on D88240
Differential Revision: https://phabricator.services.mozilla.com/D88242
220 lines
4.5 KiB
ReStructuredText
220 lines
4.5 KiB
ReStructuredText
.. _preprocessor:
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=================
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Text Preprocessor
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=================
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The build system contains a text preprocessor similar to the C preprocessor,
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meant for processing files which have no built-in preprocessor such as XUL
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and JavaScript documents. It is implemented at ``python/mozbuild/mozbuild/preprocessor.py`` and
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is typically invoked via :ref:`jar_manifests`.
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While used to preprocess CSS files, the directives are changed to begin with
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``%`` instead of ``#`` to avoid conflict of the id selectors.
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Directives
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==========
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Variable Definition
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-------------------
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define
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^^^^^^
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::
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#define variable
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#define variable value
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Defines a preprocessor variable.
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Note that, unlike the C preprocessor, instances of this variable later in the
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source are not automatically replaced (see #filter). If value is not supplied,
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it defaults to ``1``.
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Note that whitespace is significant, so ``"#define foo one"`` and
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``"#define foo one "`` is different (in the second case, ``foo`` is defined to
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be a four-character string).
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undef
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^^^^^
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::
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#undef variable
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Undefines a preprocessor variable.
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Conditionals
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------------
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if
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^^
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::
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#if variable
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#if !variable
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#if variable == string
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#if variable != string
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Disables output if the conditional is false. This can be nested to arbitrary
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depths. Note that in the equality checks, the variable must come first.
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else
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^^^^
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::
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#else
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Reverses the state of the previous conditional block; for example, if the
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last ``#if`` was true (output was enabled), an ``#else`` makes it off
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(output gets disabled).
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endif
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^^^^^
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::
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#endif
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Ends the conditional block.
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ifdef / ifndef
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^^^^^^^^^^^^^^
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::
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#ifdef variable
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#ifndef variable
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An ``#if`` conditional that is true only if the preprocessor variable
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variable is defined (in the case of ``ifdef``) or not defined (``ifndef``).
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elif / elifdef / elifndef
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^^^^^^^^^^^^^^^^^^^^^^^^^
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::
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#elif variable
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#elif !variable
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#elif variable == string
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#elif variable != string
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#elifdef variable
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#elifndef variable
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A shorthand to mean an ``#else`` combined with the relevant conditional.
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The following two blocks are equivalent::
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#ifdef foo
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block 1
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#elifdef bar
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block 2
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#endif
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::
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#ifdef foo
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block 1
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#else
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#ifdef bar
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block 2
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#endif
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#endif
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File Inclusion
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--------------
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include
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^^^^^^^
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::
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#include filename
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The file specified by filename is processed as if the contents was placed
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at this position. This also means that preprocessor conditionals can even
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be started in one file and ended in another (but is highly discouraged).
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There is no limit on depth of inclusion, or repeated inclusion of the same
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file, or self inclusion; thus, care should be taken to avoid infinite loops.
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includesubst
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^^^^^^^^^^^^
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::
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#includesubst @variable@filename
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Same as a ``#include`` except that all instances of variable in the included
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file is also expanded as in ``#filter`` substitution
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expand
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^^^^^^
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::
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#expand string
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All variables wrapped in ``__`` are replaced with their value, for this line
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only. If the variable is not defined, it expands to an empty string. For
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example, if ``foo`` has the value ``bar``, and ``baz`` is not defined, then::
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#expand This <__foo__> <__baz__> gets expanded
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Is expanded to::
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This <bar> <> gets expanded
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filter / unfilter
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^^^^^^^^^^^^^^^^^
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::
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#filter filter1 filter2 ... filterN
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#unfilter filter1 filter2 ... filterN
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``#filter`` turns on the given filter.
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Filters are run in alphabetical order on a per-line basis.
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``#unfilter`` turns off the given filter. Available filters are:
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emptyLines
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strips blank lines from the output
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dumbComments
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dumbComments: empties out any line that consists of optional whitespace
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followed by a ``//``. Good for getting rid of comments that are on their
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own lines, and being smarter with a simple regexp filter is impossible
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substitution
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all variables wrapped in @ are replaced with their value. If the
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variable is not defined, it is a fatal error. Similar to ``#expand``
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and ``#filter``
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attemptSubstitution
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all variables wrapped in ``@`` are replaced with their value, or an
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empty string if the variable is not defined. Similar to ``#expand``.
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literal
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^^^^^^^
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::
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#literal string
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Output the string (i.e. the rest of the line) literally, with no other fixups.
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This is useful to output lines starting with ``#``, or to temporarily
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disable filters.
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Other
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-----
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#error
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^^^^^^
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::
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#error string
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Cause a fatal error at this point, with the error message being the
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given string.
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