1CMAKE_MESSAGE_CONTEXT
2---------------------
3
4.. versionadded:: 3.17
5
6When enabled by the :manual:`cmake <cmake(1)>` ``--log-context`` command line
7option or the :variable:`CMAKE_MESSAGE_CONTEXT_SHOW` variable, the
8:command:`message` command converts the ``CMAKE_MESSAGE_CONTEXT`` list into a
9dot-separated string surrounded by square brackets and prepends it to each line
10for messages of log levels ``NOTICE`` and below.
11
12For logging contexts to work effectively, projects should generally
13``APPEND`` and ``POP_BACK`` an item to the current value of
14``CMAKE_MESSAGE_CONTEXT`` rather than replace it.
15Projects should not assume the message context at the top of the source tree
16is empty, as there are scenarios where the context might have already been set
17(e.g. hierarchical projects).
18
19.. warning::
20
21  Valid context names are restricted to anything that could be used
22  as a CMake variable name.  All names that begin with an underscore
23  or the string ``cmake_`` are also reserved for use by CMake and
24  should not be used by projects.
25
26Example:
27
28.. code-block:: cmake
29
30  function(bar)
31    list(APPEND CMAKE_MESSAGE_CONTEXT "bar")
32    message(VERBOSE "bar VERBOSE message")
33  endfunction()
34
35  function(baz)
36    list(APPEND CMAKE_MESSAGE_CONTEXT "baz")
37    message(DEBUG "baz DEBUG message")
38  endfunction()
39
40  function(foo)
41    list(APPEND CMAKE_MESSAGE_CONTEXT "foo")
42    bar()
43    message(TRACE "foo TRACE message")
44    baz()
45  endfunction()
46
47  list(APPEND CMAKE_MESSAGE_CONTEXT "top")
48
49  message(VERBOSE "Before `foo`")
50  foo()
51  message(VERBOSE "After `foo`")
52
53  list(POP_BACK CMAKE_MESSAGE_CONTEXT)
54
55
56Which results in the following output:
57
58.. code-block:: none
59
60  -- [top] Before `foo`
61  -- [top.foo.bar] bar VERBOSE message
62  -- [top.foo] foo TRACE message
63  -- [top.foo.baz] baz DEBUG message
64  -- [top] After `foo`
65