Files
CMake/Help/command/COMPILE_OPTIONS_SHELL.txt
Brad King ce0b983216 target_compile_options: Add syntax to specify shell strings
Options specified via `COMPILE_OPTIONS` and `INTERFACE_COMPILE_OPTIONS`
are deduplicated, but individual options can legitimately be duplicated
when grouped with other options, e.g.

    -D A -D B

After deduplication that becomes `-D A B`.  Therefore we need a way to
treat groups of options as units during deduplication.  A simple approach
is to specify each group as one option, e.g.

    "-D A" "-D B"

However, that conflicts with options that legitimately have spaces.  To
break this ambiguity, add a `SHELL:` prefix syntax to specify that an
option should be parsed like shell command line arguments after
deduplication, e.g.

    "SHELL:-D A" "SHELL:-D B"

These will survive deduplication intact, and then be parsed to produce
`-D A -D B` on the final command line.

Fixes: #15826
2018-03-14 11:10:25 -04:00

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The final set of compile options used for a target is constructed by
accumulating options from the current target and the usage requirements of
it dependencies. The set of options is de-duplicated to avoid repetition.
While beneficial for individual options, the de-duplication step can break
up option groups. For example, ``-D A -D B`` becomes ``-D A B``. One may
specify a group of options using shell-like quoting along with a ``SHELL:``
prefix. The ``SHELL:`` prefix is dropped and the rest of the option string
is parsed using the :command:`separate_arguments` ``UNIX_COMMAND`` mode.
For example, ``"SHELL:-D A" "SHELL:-D B"`` becomes ``-D A -D B``.