Refine behaviour of add_languages() when native: is missing

This improves the common case of a simple meson.build which doesn't
contain any 'native: true' targets to not require a native compiler when
cross-compiling, without needing any changes in the meson.build.

v2:
Do it the right way around!

1 files changed, 17 insertions, 2 deletions

diff --git a/docs/markdown/snippets/native_compiler_not_required.md b/docs/markdown/snippets/native_compiler_not_required.md
index 0847b2b..331b3c7 100644
--- a/docs/markdown/snippets/native_compiler_not_required.md
+++ b/docs/markdown/snippets/native_compiler_not_required.md
@@ -1,5 +1,20 @@
 ## Native (build machine) compilers not always required
 
 `add_languages()` gained a `native:` keyword, indicating if a native or cross
-compiler is to be used. Currently, for backwards compatibility, if the keyword
-is absent, that means both are used.
+compiler is to be used.
+
+For the benefit of existing simple build definitions which don't contain any
+`native: true` targets, without breaking backwards compatibility for build
+definitions which assume that the native compiler is available after
+`add_languages()`, if the `native:` keyword is absent the languages may be used
+for either the build or host machine, but are never required for the build
+machine.
+
+This changes the behaviour of the following meson fragment (when cross-compiling
+but a native compiler is not available) from reporting an error at
+`add_language` to reporting an error at `executable`.
+
+```
+add_language('c')
+executable('main', 'main.c', native: true)
+```