msetup: Update options when builddir is already configured

`meson setup -Dfoo=bar builddir` command was returning success ignoring
new option values.

This now also update options. It is useful because it means
`meson setup -Dfoo=bar builddir && ninja -C builddir` works regardless
whether builddir already exists or not, and when done in a script,
changing options in the script will automatically trigger a reconfigure
if needed. This was already possible by always passing --reconfigure
argument, but that triggers a reconfigure even when options did not
change.

1 files changed, 13 insertions, 0 deletions

diff --git a/docs/markdown/snippets/msetup.md b/docs/markdown/snippets/msetup.md
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+## Update options with `meson setup <builddir> -Dopt=value`
+
+If the build directory already exists, options are updated with their new value
+given on the command line (`-Dopt=value`). Unless `--reconfigure` is also specified,
+this won't reconfigure immediately. This has the same behaviour as
+`meson configure <builddir> -Dopt=value`.
+
+Previous Meson versions were simply a no-op.
+
+## Clear persistent cache with `meson setup --clearcache`
+
+Just like `meson configure --clearcache`, it is now possible to clear the cache
+and reconfigure in a single command with `meson setup --clearcache --reconfigure <builddir>`.