Make 'default_library' per-subproject builtin option

Currently it's just like if all builtin/base/compiler options are
yielding. This patch makes possible to have non-yielding builtin
options. The value in is overriden in this order:
 - Value from parent project
 - Value from subproject's default_options if set
 - Value from subproject() default_options if set
 - Value from command line if set

11 files changed, 117 insertions, 26 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index ae6d1c5a8..510d44323 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -1553,7 +1553,8 @@ arguments:
    that override those set in the subproject's `meson_options.txt`
    (like `default_options` in `project`, they only have effect when
    Meson is run for the first time, and command line arguments override
-   any default options in build files)
+   any default options in build files). *Since 0.54.0* `default_library`
+   built-in option can also be overridden.
  - `version` keyword argument that works just like the one in
    `dependency`. It specifies what version the subproject should be,
    as an example `>=1.0.1`
diff --git a/docs/markdown/snippets/per_subproject_builtin.md b/docs/markdown/snippets/per_subproject_builtin.md
new file mode 100644
index 000000000..44ed1c866
--- /dev/null
+++ b/docs/markdown/snippets/per_subproject_builtin.md
@@ -0,0 +1,15 @@
+## Per subproject `default_library` option
+
+The `default_library` built-in option can now be defined per subproject. This is
+useful for example when building shared libraries in the main project, but static
+link a subproject.
+
+Most of the time this would be used either by the parent project by setting
+subproject's default_options (e.g. `subproject('foo', default_options: 'default_library=static')`),
+or by the user using the command line `-Dfoo:default_library=static`.
+
+The value is overriden in this order:
+- Value from parent project
+- Value from subproject's default_options if set
+- Value from subproject() default_options if set
+- Value from command line if set
diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index cdee20d73..aea2d908e 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -364,11 +364,12 @@ class CoreData:
         self.install_guid = str(uuid.uuid4()).upper()
         self.target_guids = {}
         self.version = version
-        self.init_builtins()
-        self.backend_options = {} # : T.Dict[str, UserOption]
-        self.user_options = {} # : T.Dict[str, UserOption]
+        self.builtins = {} # : OptionDictType
+        self.builtins_per_machine = PerMachine({}, {})
+        self.backend_options = {} # : OptionDictType
+        self.user_options = {} # : OptionDictType
         self.compiler_options = PerMachine({}, {})
-        self.base_options = {} # : T.Dict[str, UserOption]
+        self.base_options = {} # : OptionDictType
         self.cross_files = self.__load_config_files(options, scratch_dir, 'cross')
         self.compilers = PerMachine(OrderedDict(), OrderedDict())
 
@@ -378,6 +379,7 @@ class CoreData:
         self.compiler_check_cache = OrderedDict()
         # Only to print a warning if it changes between Meson invocations.
         self.config_files = self.__load_config_files(options, scratch_dir, 'native')
+        self.init_builtins('')
         self.libdir_cross_fixup()
 
     @staticmethod
@@ -497,15 +499,25 @@ class CoreData:
                 raise MesonException(msg.format(option, value, prefix))
         return value.as_posix()
 
-    def init_builtins(self):
+    def init_builtins(self, subproject: str):
         # Create builtin options with default values
-        self.builtins = {}
         for key, opt in builtin_options.items():
-            self.builtins[key] = opt.init_option(key, default_prefix())
-        self.builtins_per_machine = PerMachine({}, {})
+            self.add_builtin_option(self.builtins, key, opt, subproject)
         for for_machine in iter(MachineChoice):
             for key, opt in builtin_options_per_machine.items():
-                self.builtins_per_machine[for_machine][key] = opt.init_option()
+                self.add_builtin_option(self.builtins_per_machine[for_machine], key, opt, subproject)
+
+    def add_builtin_option(self, opts_map, key, opt, subproject):
+        if subproject:
+            if opt.yielding:
+                # This option is global and not per-subproject
+                return
+            optname = subproject + ':' + key
+            value = opts_map[key].value
+        else:
+            optname = key
+            value = None
+        opts_map[optname] = opt.init_option(key, value, default_prefix())
 
     def init_backend_options(self, backend_name):
         if backend_name == 'ninja':
@@ -520,15 +532,20 @@ class CoreData:
                     'Default project to execute in Visual Studio',
                     '')
 
-    def get_builtin_option(self, optname):
+    def get_builtin_option(self, optname, subproject=''):
+        raw_optname = optname
+        if subproject:
+            optname = subproject + ':' + optname
         for opts in self._get_all_builtin_options():
             v = opts.get(optname)
+            if v is None or v.yielding:
+                v = opts.get(raw_optname)
             if v is None:
                 continue
-            if optname == 'wrap_mode':
+            if raw_optname == 'wrap_mode':
                 return WrapMode.from_string(v.value)
             return v.value
-        raise RuntimeError('Tried to get unknown builtin option %s.' % optname)
+        raise RuntimeError('Tried to get unknown builtin option %s.' % raw_optname)
 
     def _try_set_builtin_option(self, optname, value):
         for opts in self._get_all_builtin_options():
@@ -707,11 +724,13 @@ class CoreData:
                 env.cmd_line_options.setdefault(k, v)
 
         # Set default options as if they were passed to the command line.
-        # Subprojects can only define default for user options.
+        # Subprojects can only define default for user options and not yielding
+        # builtin option.
         from . import optinterpreter
         for k, v in default_options.items():
             if subproject:
-                if optinterpreter.is_invalid_name(k, log=False):
+                if (k not in builtin_options or builtin_options[k].yielding) \
+                        and optinterpreter.is_invalid_name(k, log=False):
                     continue
                 k = subproject + ':' + k
             env.cmd_line_options.setdefault(k, v)
@@ -951,7 +970,7 @@ class BuiltinOption(T.Generic[_T, _U]):
     Currently doesn't support UserIntegerOption, or a few other cases.
     """
 
-    def __init__(self, opt_type: T.Type[_U], description: str, default: T.Any, yielding: T.Optional[bool] = None, *,
+    def __init__(self, opt_type: T.Type[_U], description: str, default: T.Any, yielding: bool = True, *,
                  choices: T.Any = None):
         self.opt_type = opt_type
         self.description = description
@@ -959,9 +978,11 @@ class BuiltinOption(T.Generic[_T, _U]):
         self.choices = choices
         self.yielding = yielding
 
-    def init_option(self, name: str = 'prefix', prefix: str = '') -> _U:
+    def init_option(self, name: str, value: T.Optional[T.Any], prefix: str) -> _U:
         """Create an instance of opt_type and return it."""
-        keywords = {'yielding': self.yielding, 'value': self.prefixed_default(name, prefix)}
+        if value is None:
+            value = self.prefixed_default(name, prefix)
+        keywords = {'yielding': self.yielding, 'value': value}
         if self.choices:
             keywords['choices'] = self.choices
         return self.opt_type(self.description, **keywords)
@@ -1036,7 +1057,8 @@ builtin_options = OrderedDict([
     ('buildtype',       BuiltinOption(UserComboOption, 'Build type to use', 'debug',
                                       choices=['plain', 'debug', 'debugoptimized', 'release', 'minsize', 'custom'])),
     ('debug',           BuiltinOption(UserBooleanOption, 'Debug', True)),
-    ('default_library', BuiltinOption(UserComboOption, 'Default library type', 'shared', choices=['shared', 'static', 'both'])),
+    ('default_library', BuiltinOption(UserComboOption, 'Default library type', 'shared', choices=['shared', 'static', 'both'],
+                                      yielding=False)),
     ('errorlogs',       BuiltinOption(UserBooleanOption, "Whether to print the logs from failing tests", True)),
     ('install_umask',   BuiltinOption(UserUmaskOption, 'Default umask to apply on permissions of installed files', '022')),
     ('layout',          BuiltinOption(UserComboOption, 'Build directory layout', 'mirror', choices=['mirror', 'flat'])),
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 74882b223..d824e3c3a 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2750,19 +2750,21 @@ external dependencies (including libraries) must go to "dependencies".''')
         return result
 
     def get_option_internal(self, optname):
+        raw_optname = optname
+        if self.is_subproject():
+            optname = self.subproject + ':' + optname
+
         for opts in chain(
                 [self.coredata.base_options, compilers.base_options, self.coredata.builtins],
                 self.coredata.get_prefixed_options_per_machine(self.coredata.builtins_per_machine),
                 self.coredata.get_prefixed_options_per_machine(self.coredata.compiler_options),
         ):
             v = opts.get(optname)
+            if v is None or v.yielding:
+                v = opts.get(raw_optname)
             if v is not None:
                 return v
 
-        raw_optname = optname
-        if self.is_subproject():
-            optname = self.subproject + ':' + optname
-
         try:
             opt = self.coredata.user_options[optname]
             if opt.yielding and ':' in optname and raw_optname in self.coredata.user_options:
@@ -2869,6 +2871,7 @@ external dependencies (including libraries) must go to "dependencies".''')
         if self.environment.first_invocation:
             default_options = self.project_default_options
             default_options.update(self.default_project_options)
+            self.coredata.init_builtins(self.subproject)
         else:
             default_options = {}
         self.coredata.set_default_options(default_options, self.subproject, self.environment)
@@ -4368,7 +4371,7 @@ Try setting b_lundef to false instead.'''.format(self.coredata.base_options['b_s
         return BothLibrariesHolder(shared_holder, static_holder, self)
 
     def build_library(self, node, args, kwargs):
-        default_library = self.coredata.get_builtin_option('default_library')
+        default_library = self.coredata.get_builtin_option('default_library', self.subproject)
         if default_library == 'shared':
             return self.build_target(node, args, kwargs, SharedLibraryHolder)
         elif default_library == 'static':
diff --git a/mesonbuild/mintro.py b/mesonbuild/mintro.py
index dff5ecc36..cfa457436 100644
--- a/mesonbuild/mintro.py
+++ b/mesonbuild/mintro.py
@@ -180,9 +180,10 @@ def list_targets(builddata: build.Build, installdata, backend: backends.Backend)
     return tlist
 
 def list_buildoptions_from_source(intr: IntrospectionInterpreter) -> T.List[T.Dict[str, T.Union[str, bool, int, T.List[str]]]]:
-    return list_buildoptions(intr.coredata)
+    subprojects = [i['name'] for i in intr.project_data['subprojects']]
+    return list_buildoptions(intr.coredata, subprojects)
 
-def list_buildoptions(coredata: cdata.CoreData) -> T.List[T.Dict[str, T.Union[str, bool, int, T.List[str]]]]:
+def list_buildoptions(coredata: cdata.CoreData, subprojects: T.Optional[T.List[str]] = None) -> T.List[T.Dict[str, T.Union[str, bool, int, T.List[str]]]]:
     optlist = []  # type: T.List[T.Dict[str, T.Union[str, bool, int, T.List[str]]]]
 
     dir_option_names = ['bindir',
@@ -206,6 +207,16 @@ def list_buildoptions(coredata: cdata.CoreData) -> T.List[T.Dict[str, T.Union[st
     test_options = {k: o for k, o in coredata.builtins.items() if k in test_option_names}
     core_options = {k: o for k, o in coredata.builtins.items() if k in core_option_names}
 
+    if subprojects:
+        # Add per subproject built-in options
+        sub_core_options = {}
+        for sub in subprojects:
+            for k, o in core_options.items():
+                if o.yielding:
+                    continue
+                sub_core_options[sub + ':' + k] = o
+        core_options.update(sub_core_options)
+
     def add_keys(options: T.Dict[str, cdata.UserOption], section: str, machine: str = 'any') -> None:
         for key in sorted(options.keys()):
             opt = options[key]
diff --git a/test cases/common/229 persubproject options/foo.c b/test cases/common/229 persubproject options/foo.c
new file mode 100644
index 000000000..63e4de6a3
--- /dev/null
+++ b/test cases/common/229 persubproject options/foo.c
@@ -0,0 +1,5 @@
+int foo(void);
+
+int foo(void) {
+  return 0;
+}
diff --git a/test cases/common/229 persubproject options/meson.build b/test cases/common/229 persubproject options/meson.build
new file mode 100644
index 000000000..6a76697e2
--- /dev/null
+++ b/test cases/common/229 persubproject options/meson.build
@@ -0,0 +1,10 @@
+project('persubproject options', 'c', default_options : ['default_library=both'])
+
+assert(get_option('default_library') == 'both', 'Parent default_library should be "both"')
+
+# Check it build both by calling a method only both_libraries target implement
+lib = library('lib1', 'foo.c')
+lib.get_static_lib()
+
+subproject('sub1')
+subproject('sub2', default_options : ['default_library=static'])
diff --git a/test cases/common/229 persubproject options/subprojects/sub1/foo.c b/test cases/common/229 persubproject options/subprojects/sub1/foo.c
new file mode 100644
index 000000000..63e4de6a3
--- /dev/null
+++ b/test cases/common/229 persubproject options/subprojects/sub1/foo.c
@@ -0,0 +1,5 @@
+int foo(void);
+
+int foo(void) {
+  return 0;
+}
diff --git a/test cases/common/229 persubproject options/subprojects/sub1/meson.build b/test cases/common/229 persubproject options/subprojects/sub1/meson.build
new file mode 100644
index 000000000..7afc934e6
--- /dev/null
+++ b/test cases/common/229 persubproject options/subprojects/sub1/meson.build
@@ -0,0 +1,7 @@
+project('sub1', 'c')
+
+assert(get_option('default_library') == 'both', 'Should inherit parent project default_library')
+
+# Check it build both by calling a method only both_libraries target implement
+lib = library('lib1', 'foo.c')
+lib.get_static_lib()
diff --git a/test cases/common/229 persubproject options/subprojects/sub2/foo.c b/test cases/common/229 persubproject options/subprojects/sub2/foo.c
new file mode 100644
index 000000000..63e4de6a3
--- /dev/null
+++ b/test cases/common/229 persubproject options/subprojects/sub2/foo.c
@@ -0,0 +1,5 @@
+int foo(void);
+
+int foo(void) {
+  return 0;
+}
diff --git a/test cases/common/229 persubproject options/subprojects/sub2/meson.build b/test cases/common/229 persubproject options/subprojects/sub2/meson.build
new file mode 100644
index 000000000..546884de3
--- /dev/null
+++ b/test cases/common/229 persubproject options/subprojects/sub2/meson.build
@@ -0,0 +1,7 @@
+project('sub2', 'c', default_options : ['default_library=shared'])
+
+assert(get_option('default_library') == 'static', 'Parent should override default_library')
+
+# If it doesn't build only a static library, it would make target name clash.
+library('lib1', 'foo.c')
+shared_library('lib1', 'foo.c')