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.

6 files changed, 59 insertions, 22 deletions

diff --git a/docs/markdown/Commands.md b/docs/markdown/Commands.md
index 75b2281..efc316c 100644
--- a/docs/markdown/Commands.md
+++ b/docs/markdown/Commands.md
@@ -244,6 +244,17 @@ Configures a build directory for the Meson project.
 was no COMMAND supplied). However, supplying the command is necessary to avoid
 clashes with future added commands, so "setup" should be used explicitly.
 
+*Since 1.1.0* `--reconfigure` is allowed even if the build directory does not
+already exist, that argument is ignored in that case.
+
+*Since 1.3.0* 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`.
+
+*Since 1.3.0* It is possible to clear the cache and reconfigure in a single command
+with `meson setup --clearcache --reconfigure <builddir>`.
+
 {{ setup_arguments.inc }}
 
 See [Meson introduction
diff --git a/docs/markdown/snippets/msetup.md b/docs/markdown/snippets/msetup.md
new file mode 100644
index 0000000..f68313d
--- /dev/null
+++ b/docs/markdown/snippets/msetup.md
@@ -0,0 +1,13 @@
+## 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>`.
diff --git a/mesonbuild/mconf.py b/mesonbuild/mconf.py
index d4ecce8..9f6c685 100644
--- a/mesonbuild/mconf.py
+++ b/mesonbuild/mconf.py
@@ -301,9 +301,7 @@ class Conf:
         for m in mismatching:
             mlog.log(f'{m[0]:21}{m[1]:10}{m[2]:10}')
 
-def run(options: argparse.Namespace) -> int:
-    coredata.parse_cmd_line_options(options)
-    builddir = os.path.abspath(os.path.realpath(options.builddir))
+def run_impl(options: argparse.Namespace, builddir: str) -> int:
     print_only = not options.cmd_line_options and not options.clearcache
     c = None
     try:
@@ -334,3 +332,8 @@ def run(options: argparse.Namespace) -> int:
         # Pager quit before we wrote everything.
         pass
     return 0
+
+def run(options: argparse.Namespace) -> int:
+    coredata.parse_cmd_line_options(options)
+    builddir = os.path.abspath(os.path.realpath(options.builddir))
+    return run_impl(options, builddir)
diff --git a/mesonbuild/msetup.py b/mesonbuild/msetup.py
index 73c9fb3..4ff6000 100644
--- a/mesonbuild/msetup.py
+++ b/mesonbuild/msetup.py
@@ -55,15 +55,15 @@ def add_arguments(parser: argparse.ArgumentParser) -> None:
                         help='Wipe build directory and reconfigure using previous command line options. ' +
                              'Useful when build directory got corrupted, or when rebuilding with a ' +
                              'newer version of meson.')
+    parser.add_argument('--clearcache', action='store_true', default=False,
+                        help='Clear cached state (e.g. found dependencies). Since 1.3.0.')
     parser.add_argument('builddir', nargs='?', default=None)
     parser.add_argument('sourcedir', nargs='?', default=None)
 
 class MesonApp:
     def __init__(self, options: argparse.Namespace) -> None:
-        (self.source_dir, self.build_dir) = self.validate_dirs(options.builddir,
-                                                               options.sourcedir,
-                                                               options.reconfigure,
-                                                               options.wipe)
+        self.options = options
+        (self.source_dir, self.build_dir) = self.validate_dirs()
         if options.wipe:
             # Make a copy of the cmd line file to make sure we can always
             # restore that file if anything bad happens. For example if
@@ -96,8 +96,6 @@ class MesonApp:
                         os.makedirs(os.path.dirname(f), exist_ok=True)
                         shutil.move(b, f)
 
-        self.options = options
-
     def has_build_file(self, dirname: str) -> bool:
         fname = os.path.join(dirname, environment.build_filename)
         return os.path.exists(fname)
@@ -144,8 +142,8 @@ class MesonApp:
         with open(os.path.join(build_dir, '.hgignore'), 'w', encoding='utf-8') as ofile:
             ofile.write(hg_ignore_file)
 
-    def validate_dirs(self, dir1: T.Optional[str], dir2: T.Optional[str], reconfigure: bool, wipe: bool) -> T.Tuple[str, str]:
-        (src_dir, build_dir) = self.validate_core_dirs(dir1, dir2)
+    def validate_dirs(self) -> T.Tuple[str, str]:
+        (src_dir, build_dir) = self.validate_core_dirs(self.options.builddir, self.options.sourcedir)
         if Path(build_dir) in Path(src_dir).parents:
             raise MesonException(f'Build directory {build_dir} cannot be a parent of source directory {src_dir}')
         if not os.listdir(build_dir):
@@ -155,21 +153,17 @@ class MesonApp:
         has_valid_build = os.path.exists(os.path.join(priv_dir, 'coredata.dat'))
         has_partial_build = os.path.isdir(priv_dir)
         if has_valid_build:
-            if not reconfigure and not wipe:
+            if not self.options.reconfigure and not self.options.wipe:
                 print('Directory already configured.\n\n'
                       'Just run your build command (e.g. ninja) and Meson will regenerate as necessary.\n'
-                      'If ninja fails, run "ninja reconfigure" or "meson setup --reconfigure"\n'
-                      'to force Meson to regenerate.\n\n'
+                      'Run "meson setup --reconfigure to force Meson to regenerate.\n\n'
                       'If build failures persist, run "meson setup --wipe" to rebuild from scratch\n'
-                      'using the same options as passed when configuring the build.\n'
-                      'To change option values, run "meson configure" instead.')
-                # FIXME: This returns success and ignores new option values from CLI.
-                # We should either make this a hard error, or update options and
-                # return success.
-                # Note that making this an error would not be backward compatible (and also isn't
-                # universally agreed on): https://github.com/mesonbuild/meson/pull/4249.
+                      'using the same options as passed when configuring the build.')
+                if self.options.cmd_line_options:
+                    from . import mconf
+                    raise SystemExit(mconf.run_impl(self.options, build_dir))
                 raise SystemExit(0)
-        elif not has_partial_build and wipe:
+        elif not has_partial_build and self.options.wipe:
             raise MesonException(f'Directory is not empty and does not contain a previous build:\n{build_dir}')
         return src_dir, build_dir
 
@@ -179,6 +173,8 @@ class MesonApp:
         mlog.initialize(env.get_log_dir(), self.options.fatal_warnings)
         if self.options.profile:
             mlog.set_timestamp_start(time.monotonic())
+        if self.options.clearcache:
+            env.coredata.clear_cache()
         with mesonlib.BuildDirLock(self.build_dir):
             return self._generate(env, capture, vslite_ctx)
 
diff --git a/unittests/baseplatformtests.py b/unittests/baseplatformtests.py
index 03ab1c5..514f3b7 100644
--- a/unittests/baseplatformtests.py
+++ b/unittests/baseplatformtests.py
@@ -303,6 +303,13 @@ class BasePlatformTests(TestCase):
             ensure_backend_detects_changes(self.backend)
         self._run(self.mconf_command + arg + [self.builddir])
 
+    def getconf(self, optname: str):
+        opts = self.introspect('--buildoptions')
+        for x in opts:
+            if x.get('name') == optname:
+                return x.get('value')
+        self.fail(f'Option {optname} not found')
+
     def wipe(self):
         windows_proof_rmtree(self.builddir)
 
diff --git a/unittests/platformagnostictests.py b/unittests/platformagnostictests.py
index fd01293..efe3109 100644
--- a/unittests/platformagnostictests.py
+++ b/unittests/platformagnostictests.py
@@ -183,6 +183,13 @@ class PlatformAgnosticTests(BasePlatformTests):
         Path(self.builddir, 'dummy').touch()
         self.init(testdir, extra_args=['--reconfigure'])
 
+        # Setup a valid builddir should update options but not reconfigure
+        self.assertEqual(self.getconf('buildtype'), 'debug')
+        o = self.init(testdir, extra_args=['-Dbuildtype=release'])
+        self.assertIn('Directory already configured', o)
+        self.assertNotIn('The Meson build system', o)
+        self.assertEqual(self.getconf('buildtype'), 'release')
+
         # Wipe of empty builddir should work
         self.new_builddir()
         self.init(testdir, extra_args=['--wipe'])