Add depfile to configure_file()

In qemu, minikconf generates a depfile that meson could use to
automatically reconfigure on dependency change.

Note: someone clever can perhaps find a way to express this with a
ninja rule & depfile=. I didn't manage, so I wrote a simple depfile
parser.

2 files changed, 6 insertions, 0 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index 6009d30..176cde4 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -260,6 +260,9 @@ These are all the supported keyword arguments:
   substitutions.
 - `copy` *(added 0.47.0)* as explained above, if specified Meson only
   copies the file from input to output.
+- `depfile` *(added 0.52.0)* is a dependency file that the command can write listing
+  all the additional files this target depends on. A change
+  in any one of these files triggers a reconfiguration.
 - `format` *(added 0.46.0)* the format of defines. It defaults to `meson`, and so substitutes
 `#mesondefine` statements and variables surrounded by `@` characters, you can also use `cmake`
 to replace `#cmakedefine` statements and variables with the `${variable}` syntax. Finally you can use
diff --git a/docs/markdown/snippets/configure_file_enhancements.md b/docs/markdown/snippets/configure_file_enhancements.md
index 35a64b4..7fee7b2 100644
--- a/docs/markdown/snippets/configure_file_enhancements.md
+++ b/docs/markdown/snippets/configure_file_enhancements.md
@@ -1,3 +1,6 @@
 ## Enhancements to `configure_file()`
 
 `input:` now accepts multiple input file names for `command:`-configured file.
+
+`depfile:` keyword argument is now accepted. The dependency file can
+list all the additional files the configure target depends on.