fix regression that broke type checking of CustomTarget outputs

We validate a few things here, such as the non-presence of '@INPUT' in
an output name. These got moved out of the CustomTarget constructor in
commit 11f96380351a88059ec55f1070fdebc1b1033117 and into KwargInfo, but
only for kwargs that took multiple values. This caused configure_file()
and unstable_rust.bindgen() to stop checking for this.

Add a shared single-output KW and use it in both places. This now
dispatches to _output_validator.

configure_file now validates subdirectories in output names the same way
we do elsewhere, directly in the typed_kwargs and by specifying the
erroring kwarg.

1 files changed, 1 insertions, 1 deletions

diff --git a/test cases/failing/26 output subdir/test.json b/test cases/failing/26 output subdir/test.json
index 796468d..df09726 100644
--- a/test cases/failing/26 output subdir/test.json
+++ b/test cases/failing/26 output subdir/test.json
@@ -1,7 +1,7 @@
 {
   "stdout": [
     {
-      "line": "test cases/failing/26 output subdir/meson.build:3:0: ERROR: Output file name must not contain a subdirectory."
+      "line": "test cases/failing/26 output subdir/meson.build:3:0: ERROR: configure_file keyword argument \"output\" Output 'subdir/foo' must not contain a path segment."
     }
   ]
 }