WIP: Create enum to use instead of strings for language

26 files changed, 190 insertions, 98 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index e765466..22fe8f4 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -32,7 +32,7 @@ from ..compilers import (Compiler, CompilerArgs, CCompiler, FortranCompiler,
                          PGICCompiler, VisualStudioLikeCompiler)
 from ..linkers import ArLinker
 from ..mesonlib import (
-    File, LibType, MachineChoice, MesonException, OrderedSet, PerMachine,
+    File, LibType, Language, MachineChoice, MesonException, OrderedSet, PerMachine,
     ProgressBar, quote_arg, unholder,
 )
 from ..mesonlib import get_compiler_for_source, has_path_sep
@@ -1376,12 +1376,12 @@ int dummy;
         return PerMachine('_FOR_BUILD', '')[for_machine]
 
     @classmethod
-    def get_compiler_rule_name(cls, lang: str, for_machine: MachineChoice) -> str:
-        return '%s_COMPILER%s' % (lang, cls.get_rule_suffix(for_machine))
+    def get_compiler_rule_name(cls, lang: Language, for_machine: MachineChoice) -> str:
+        return '%s_COMPILER%s' % (lang.get_lower_case_name(), cls.get_rule_suffix(for_machine))
 
     @classmethod
-    def get_pch_rule_name(cls, lang: str, for_machine: MachineChoice) -> str:
-        return '%s_PCH%s' % (lang, cls.get_rule_suffix(for_machine))
+    def get_pch_rule_name(cls, lang: Language, for_machine: MachineChoice) -> str:
+        return '%s_PCH%s' % (lang.get_lower_case_name(), cls.get_rule_suffix(for_machine))
 
     @classmethod
     def compiler_to_rule_name(cls, compiler: Compiler) -> str:
diff --git a/mesonbuild/cmake/executor.py b/mesonbuild/cmake/executor.py
index a41b293..ddf2a6d 100644
--- a/mesonbuild/cmake/executor.py
+++ b/mesonbuild/cmake/executor.py
@@ -250,7 +250,7 @@ class CMakeExecutor:
         fallback = os.path.realpath(__file__)  # A file used as a fallback wehen everything else fails
         compilers = self.environment.coredata.compilers[MachineChoice.BUILD]
 
-        def make_abs(exe: str, lang: str) -> str:
+        def make_abs(exe: str, lang: Language) -> str:
             if os.path.isabs(exe):
                 return exe
 
@@ -260,7 +260,7 @@ class CMakeExecutor:
                 p = fallback
             return p
 
-        def choose_compiler(lang: str) -> T.Tuple[str, str]:
+        def choose_compiler(lang: Language) -> T.Tuple[str, str]:
             exe_list = []
             if lang in compilers:
                 exe_list = compilers[lang].get_exelist()
diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index 1bc9e84..52a5157 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -16,7 +16,7 @@ import os.path
 import typing as T
 
 from .. import coredata
-from ..mesonlib import MachineChoice, MesonException, mlog, version_compare
+from ..mesonlib import Language, MachineChoice, MesonException, mlog, version_compare
 from ..linkers import LinkerEnvVarsMixin
 from .c_function_attributes import C_FUNC_ATTRIBUTES
 from .mixins.clike import CLikeCompiler
@@ -50,7 +50,7 @@ class CCompiler(CLikeCompiler, Compiler):
         except KeyError:
             raise MesonException('Unknown function attribute "{}"'.format(name))
 
-    language = 'c'
+    language = Language.C
 
     def __init__(self, exelist, version, for_machine: MachineChoice, is_cross: bool,
                  info: 'MachineInfo', exe_wrapper: T.Optional[str] = None, **kwargs):
diff --git a/mesonbuild/compilers/compilers.py b/mesonbuild/compilers/compilers.py
index 3d3a503..ffd8d06 100644
--- a/mesonbuild/compilers/compilers.py
+++ b/mesonbuild/compilers/compilers.py
@@ -26,7 +26,7 @@ from .. import coredata
 from .. import mlog
 from .. import mesonlib
 from ..mesonlib import (
-    EnvironmentException, MachineChoice, MesonException,
+    EnvironmentException, Language, MachineChoice, MesonException,
     Popen_safe, split_args
 )
 from ..envconfig import (
@@ -51,52 +51,67 @@ lib_suffixes = ('a', 'lib', 'dll', 'dll.a', 'dylib', 'so')
 # Mapping of language to suffixes of files that should always be in that language
 # This means we can't include .h headers here since they could be C, C++, ObjC, etc.
 lang_suffixes = {
-    'c': ('c',),
-    'cpp': ('cpp', 'cc', 'cxx', 'c++', 'hh', 'hpp', 'ipp', 'hxx'),
-    'cuda': ('cu',),
+    Language.C: ('c',),
+    Language.CPP: ('cpp', 'cc', 'cxx', 'c++', 'hh', 'hpp', 'ipp', 'hxx'),
+    Language.CUDA: ('cu',),
     # f90, f95, f03, f08 are for free-form fortran ('f90' recommended)
     # f, for, ftn, fpp are for fixed-form fortran ('f' or 'for' recommended)
-    'fortran': ('f90', 'f95', 'f03', 'f08', 'f', 'for', 'ftn', 'fpp'),
-    'd': ('d', 'di'),
-    'objc': ('m',),
-    'objcpp': ('mm',),
-    'rust': ('rs',),
-    'vala': ('vala', 'vapi', 'gs'),
-    'cs': ('cs',),
-    'swift': ('swift',),
-    'java': ('java',),
+    Language.FORTRAN: ('f90', 'f95', 'f03', 'f08', 'f', 'for', 'ftn', 'fpp'),
+    Language.D: ('d', 'di'),
+    Language.OBJC: ('m',),
+    Language.OBJCPP: ('mm',),
+    Language.RUST: ('rs',),
+    Language.VALA: ('vala', 'vapi', 'gs'),
+    Language.CS: ('cs',),
+    Language.SWIFT: ('swift',),
+    Language.JAVA: ('java',),
 }
 all_languages = lang_suffixes.keys()
-cpp_suffixes = lang_suffixes['cpp'] + ('h',)
-c_suffixes = lang_suffixes['c'] + ('h',)
+cpp_suffixes = lang_suffixes[Language.CPP] + ('h',)
+c_suffixes = lang_suffixes[Language.C] + ('h',)
 # List of languages that by default consume and output libraries following the
 # C ABI; these can generally be used interchangebly
-clib_langs = ('objcpp', 'cpp', 'objc', 'c', 'fortran',)
+clib_langs = (Language.OBJCPP, Language.CPP, Language.OBJC, Language.C, Language.FORTRAN,)
 # List of languages that can be linked with C code directly by the linker
 # used in build.py:process_compilers() and build.py:get_dynamic_linker()
-clink_langs = ('d', 'cuda') + clib_langs
+clink_langs = (Language.D, Language.CUDA) + clib_langs
 clink_suffixes = ()
-for _l in clink_langs + ('vala',):
+for _l in clink_langs + (Language.VALA,):
     clink_suffixes += lang_suffixes[_l]
 clink_suffixes += ('h', 'll', 's')
 all_suffixes = set(itertools.chain(*lang_suffixes.values(), clink_suffixes))
 
 # Languages that should use LDFLAGS arguments when linking.
-languages_using_ldflags = {'objcpp', 'cpp', 'objc', 'c', 'fortran', 'd', 'cuda'}
+languages_using_ldflags = {
+    Language.OBJCPP,
+    Language.CPP,
+    Language.OBJC,
+    Language.C,
+    Language.FORTRAN,
+    Language.D,
+    Language.CUDA
+}
 # Languages that should use CPPFLAGS arguments when linking.
-languages_using_cppflags = {'c', 'cpp', 'objc', 'objcpp'}
+languages_using_cppflags = {
+    Language.C,
+    Language.CPP,
+    Language.OBJC,
+    Language.OBJCPP,
+}
 soregex = re.compile(r'.*\.so(\.[0-9]+)?(\.[0-9]+)?(\.[0-9]+)?$')
 
 # Environment variables that each lang uses.
-cflags_mapping = {'c': 'CFLAGS',
-                  'cpp': 'CXXFLAGS',
-                  'cuda': 'CUFLAGS',
-                  'objc': 'OBJCFLAGS',
-                  'objcpp': 'OBJCXXFLAGS',
-                  'fortran': 'FFLAGS',
-                  'd': 'DFLAGS',
-                  'vala': 'VALAFLAGS',
-                  'rust': 'RUSTFLAGS'}
+cflags_mapping = {
+    Language.C: 'CFLAGS',
+    Language.CPP: 'CXXFLAGS',
+    Language.CUDA: 'CUFLAGS',
+    Language.OBJC: 'OBJCFLAGS',
+    Language.OBJCPP: 'OBJCXXFLAGS',
+    Language.FORTRAN: 'FFLAGS',
+    Language.D: 'DFLAGS',
+    Language.VALA: 'VALAFLAGS',
+    Language.RUST: 'RUSTFLAGS',
+}
 
 unixy_compiler_internal_libs = ('m', 'c', 'pthread', 'dl', 'rt')
 # execinfo is a compiler lib on FreeBSD and NetBSD
@@ -569,7 +584,7 @@ class CompilerArgs(collections.abc.MutableSequence):
         return False
 
     def need_to_split_linker_args(self):
-        return isinstance(self.compiler, Compiler) and self.compiler.get_language() == 'd'
+        return isinstance(self.compiler, Compiler) and self.compiler.get_language() == Language.D
 
     def to_native(self, copy: bool = False) -> T.List[str]:
         # Check if we need to add --start/end-group for circular dependencies
@@ -1227,7 +1242,7 @@ def get_largefile_args(compiler):
     return []
 
 
-def get_args_from_envvars(lang: str,
+def get_args_from_envvars(lang: Language,
                           for_machine: MachineChoice,
                           is_cross: bool,
                           use_linker_args: bool) -> T.Tuple[T.List[str], T.List[str]]:
@@ -1264,7 +1279,7 @@ def get_args_from_envvars(lang: str,
     return compile_flags, link_flags
 
 
-def get_global_options(lang: str,
+def get_global_options(lang: Language,
                        comp: T.Type[Compiler],
                        for_machine: MachineChoice,
                        is_cross: bool,
@@ -1288,7 +1303,7 @@ def get_global_options(lang: str,
         comp.INVOKES_LINKER)
 
     for k, o in opts.items():
-        user_k = lang + '_' + k
+        user_k = lang.get_lower_case_name() + '_' + k
         if user_k in properties:
             # Get from configuration files.
             o.set_value(properties[user_k])
diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index d30017f..c4c7da5 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -19,7 +19,7 @@ import typing as T
 
 from .. import coredata
 from .. import mlog
-from ..mesonlib import MesonException, MachineChoice, version_compare
+from ..mesonlib import Language, MesonException, MachineChoice, version_compare
 
 from ..linkers import LinkerEnvVarsMixin
 from .compilers import (
@@ -60,7 +60,7 @@ class CPPCompiler(CLikeCompiler, Compiler):
         except KeyError:
             raise MesonException('Unknown function attribute "{}"'.format(name))
 
-    language = 'cpp'
+    language = Language.CPP
 
     def __init__(self, exelist, version, for_machine: MachineChoice, is_cross: bool,
                  info: 'MachineInfo', exe_wrap: T.Optional[str] = None, **kwargs):
diff --git a/mesonbuild/compilers/cs.py b/mesonbuild/compilers/cs.py
index 843348e..bc917cb 100644
--- a/mesonbuild/compilers/cs.py
+++ b/mesonbuild/compilers/cs.py
@@ -15,7 +15,7 @@
 import os.path, subprocess
 import typing as T
 
-from ..mesonlib import EnvironmentException
+from ..mesonlib import Language, EnvironmentException
 
 from .compilers import Compiler, MachineChoice, mono_buildtype_args
 from .mixins.islinker import BasicLinkerIsCompilerMixin
@@ -34,7 +34,7 @@ cs_optimization_args = {'0': [],
 
 class CsCompiler(BasicLinkerIsCompilerMixin, Compiler):
 
-    language = 'cs'
+    language = Language.CS
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  info: 'MachineInfo', comp_id, runner=None):
diff --git a/mesonbuild/compilers/cuda.py b/mesonbuild/compilers/cuda.py
index e839f53..00233b0 100644
--- a/mesonbuild/compilers/cuda.py
+++ b/mesonbuild/compilers/cuda.py
@@ -18,9 +18,14 @@ from functools import partial
 
 from .. import coredata
 from .. import mlog
-from ..mesonlib import EnvironmentException, MachineChoice, Popen_safe, OptionOverrideProxy, is_windows, LibType
-from .compilers import (Compiler, cuda_buildtype_args, cuda_optimization_args,
-                        cuda_debug_args)
+from ..mesonlib import (
+    EnvironmentException, Language, LibType, MachineChoice, OptionOverrideProxy,
+    Popen_safe, is_windows
+)
+from .compilers import (
+    Compiler, cuda_buildtype_args, cuda_optimization_args,
+    cuda_debug_args
+)
 
 if T.TYPE_CHECKING:
     from ..environment import Environment  # noqa: F401
@@ -30,7 +35,7 @@ if T.TYPE_CHECKING:
 class CudaCompiler(Compiler):
 
     LINKER_PREFIX = '-Xlinker='
-    language = 'cuda'
+    language = Language.CUDA
 
     _universal_flags = {'compiler': ['-I', '-D', '-U', '-E'], 'linker': ['-l', '-L']}
 
diff --git a/mesonbuild/compilers/d.py b/mesonbuild/compilers/d.py
index a83e221..caa8e44 100644
--- a/mesonbuild/compilers/d.py
+++ b/mesonbuild/compilers/d.py
@@ -16,7 +16,7 @@ import os.path, subprocess
 import typing as T
 
 from ..mesonlib import (
-    EnvironmentException, MachineChoice, version_compare,
+    EnvironmentException, Language, MachineChoice, version_compare,
 )
 
 from .compilers import (
@@ -436,7 +436,7 @@ class DCompiler(Compiler):
         'mtd': ['-mscrtlib=libcmtd'],
     }
 
-    language = 'd'
+    language = Language.D
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  info: 'MachineInfo', arch, is_cross, exe_wrapper, **kwargs):
diff --git a/mesonbuild/compilers/fortran.py b/mesonbuild/compilers/fortran.py
index 01283a1..2b20aa4 100644
--- a/mesonbuild/compilers/fortran.py
+++ b/mesonbuild/compilers/fortran.py
@@ -32,7 +32,7 @@ from .mixins.pgi import PGICompiler
 from .. import mlog
 
 from mesonbuild.mesonlib import (
-    version_compare, EnvironmentException, MesonException, MachineChoice, LibType
+    version_compare, EnvironmentException, Language, MesonException, MachineChoice, LibType
 )
 
 if T.TYPE_CHECKING:
@@ -41,7 +41,7 @@ if T.TYPE_CHECKING:
 
 class FortranCompiler(CLikeCompiler, Compiler):
 
-    language = 'fortran'
+    language = Language.FORTRAN
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross, info: 'MachineInfo', exe_wrapper=None, **kwargs):
diff --git a/mesonbuild/compilers/java.py b/mesonbuild/compilers/java.py
index 5aeb250..c9a7af9 100644
--- a/mesonbuild/compilers/java.py
+++ b/mesonbuild/compilers/java.py
@@ -17,7 +17,7 @@ import shutil
 import subprocess
 import typing as T
 
-from ..mesonlib import EnvironmentException, MachineChoice
+from ..mesonlib import EnvironmentException, Language, MachineChoice
 from .compilers import Compiler, java_buildtype_args
 from .mixins.islinker import BasicLinkerIsCompilerMixin
 
@@ -26,7 +26,7 @@ if T.TYPE_CHECKING:
 
 class JavaCompiler(BasicLinkerIsCompilerMixin, Compiler):
 
-    language = 'java'
+    language = Language.JAVA
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  info: 'MachineInfo'):
diff --git a/mesonbuild/compilers/mixins/clike.py b/mesonbuild/compilers/mixins/clike.py
index 24f4796..260342e 100644
--- a/mesonbuild/compilers/mixins/clike.py
+++ b/mesonbuild/compilers/mixins/clike.py
@@ -304,7 +304,7 @@ class CLikeCompiler:
         cargs += cleaned_sys_args
 
         if mode == 'link':
-            ld_value = env.lookup_binary_entry(self.for_machine, self.language + '_ld')
+            ld_value = env.lookup_binary_entry(self.for_machine, self.language.get_lower_case_name() + '_ld')
             if ld_value is not None:
                 largs += self.use_linker_args(ld_value[0])
 
diff --git a/mesonbuild/compilers/mixins/gnu.py b/mesonbuild/compilers/mixins/gnu.py
index 3526a91..a1541bd 100644
--- a/mesonbuild/compilers/mixins/gnu.py
+++ b/mesonbuild/compilers/mixins/gnu.py
@@ -84,7 +84,7 @@ gnu_color_args = {
 
 
 @functools.lru_cache(maxsize=None)
-def gnulike_default_include_dirs(compiler: T.Tuple[str], lang: str) -> T.List[str]:
+def gnulike_default_include_dirs(compiler: T.Tuple[str], lang: mesonlib.Language) -> T.List[str]:
     lang_map = {
         'c': 'c',
         'cpp': 'c++',
diff --git a/mesonbuild/compilers/mixins/pgi.py b/mesonbuild/compilers/mixins/pgi.py
index 77a7a28..e5df38e 100644
--- a/mesonbuild/compilers/mixins/pgi.py
+++ b/mesonbuild/compilers/mixins/pgi.py
@@ -18,6 +18,7 @@ import typing as T
 import os
 from pathlib import Path
 
+from ...mesonlib import Language
 from ..compilers import clike_debug_args, clike_optimization_args
 
 pgi_buildtype_args = {
@@ -87,7 +88,7 @@ class PGICompiler:
     def get_pch_use_args(self, pch_dir: str, header: str) -> T.List[str]:
         # PGI supports PCH for C++ only.
         hdr = Path(pch_dir).resolve().parent / header
-        if self.language == 'cpp':
+        if self.language == Language.CPP:
             return ['--pch',
                     '--pch_dir', str(hdr.parent),
                     '-I{}'.format(hdr.parent)]
diff --git a/mesonbuild/compilers/objc.py b/mesonbuild/compilers/objc.py
index 52d258d..b042bc5 100644
--- a/mesonbuild/compilers/objc.py
+++ b/mesonbuild/compilers/objc.py
@@ -15,7 +15,7 @@
 import os.path, subprocess
 import typing as T
 
-from ..mesonlib import EnvironmentException, MachineChoice
+from ..mesonlib import EnvironmentException, Language, MachineChoice
 
 from .compilers import Compiler
 from .mixins.clike import CLikeCompiler
@@ -28,7 +28,7 @@ if T.TYPE_CHECKING:
 
 class ObjCCompiler(CLikeCompiler, Compiler):
 
-    language = 'objc'
+    language = Language.OBJC
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo',
diff --git a/mesonbuild/compilers/objcpp.py b/mesonbuild/compilers/objcpp.py
index c8b422b..4cfb1ab 100644
--- a/mesonbuild/compilers/objcpp.py
+++ b/mesonbuild/compilers/objcpp.py
@@ -15,7 +15,7 @@
 import os.path, subprocess
 import typing as T
 
-from ..mesonlib import EnvironmentException, MachineChoice
+from ..mesonlib import EnvironmentException, Language, MachineChoice
 
 from .mixins.clike import CLikeCompiler
 from .compilers import Compiler
@@ -27,7 +27,7 @@ if T.TYPE_CHECKING:
 
 class ObjCPPCompiler(CLikeCompiler, Compiler):
 
-    language = 'objcpp'
+    language = Language.OBJCPP
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo',
diff --git a/mesonbuild/compilers/rust.py b/mesonbuild/compilers/rust.py
index c2e21c4..46832c5 100644
--- a/mesonbuild/compilers/rust.py
+++ b/mesonbuild/compilers/rust.py
@@ -15,7 +15,7 @@
 import subprocess, os.path
 import typing as T
 
-from ..mesonlib import EnvironmentException, MachineChoice, Popen_safe
+from ..mesonlib import EnvironmentException, Language, MachineChoice, Popen_safe
 from .compilers import Compiler, rust_buildtype_args, clike_debug_args
 
 if T.TYPE_CHECKING:
@@ -33,7 +33,7 @@ rust_optimization_args = {'0': [],
 class RustCompiler(Compiler):
 
     # rustc doesn't invoke the compiler itself, it doesn't need a LINKER_PREFIX
-    language = 'rust'
+    language = Language.RUST
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross, info: 'MachineInfo', exe_wrapper=None, **kwargs):
diff --git a/mesonbuild/compilers/swift.py b/mesonbuild/compilers/swift.py
index 1942120..c7d0041 100644
--- a/mesonbuild/compilers/swift.py
+++ b/mesonbuild/compilers/swift.py
@@ -15,7 +15,7 @@
 import subprocess, os.path
 import typing as T
 
-from ..mesonlib import EnvironmentException, MachineChoice
+from ..mesonlib import EnvironmentException, Language, MachineChoice
 
 from .compilers import Compiler, swift_buildtype_args, clike_debug_args
 
@@ -33,7 +33,7 @@ swift_optimization_args = {'0': [],
 class SwiftCompiler(Compiler):
 
     LINKER_PREFIX = ['-Xlinker']
-    language = 'swift'
+    language = Language.SWIFT
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross, info: 'MachineInfo', **kwargs):
diff --git a/mesonbuild/compilers/vala.py b/mesonbuild/compilers/vala.py
index a5d49b6..635cce3 100644
--- a/mesonbuild/compilers/vala.py
+++ b/mesonbuild/compilers/vala.py
@@ -16,7 +16,7 @@ import os.path
 import typing as T
 
 from .. import mlog
-from ..mesonlib import EnvironmentException, MachineChoice, version_compare
+from ..mesonlib import EnvironmentException, Language, MachineChoice, version_compare
 
 from .compilers import Compiler
 
@@ -25,7 +25,7 @@ if T.TYPE_CHECKING:
 
 class ValaCompiler(Compiler):
 
-    language = 'vala'
+    language = Language.VALA
 
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross, info: 'MachineInfo'):
diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index 0b79084..8d043aa 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -19,7 +19,7 @@ from itertools import chain
 from pathlib import PurePath
 from collections import OrderedDict, defaultdict
 from .mesonlib import (
-    MesonException, MachineChoice, PerMachine, OrderedSet,
+    Language, MesonException, MachineChoice, PerMachine, OrderedSet,
     default_libdir, default_libexecdir, default_prefix, split_args
 )
 from .envconfig import get_env_var_pair
@@ -373,7 +373,7 @@ class CoreData:
         self.compiler_options = PerMachine(
             defaultdict(dict),
             defaultdict(dict),
-        ) # : PerMachine[T.defaultdict[str, OptionDictType]]
+        ) # : PerMachine[T.defaultdict[Language, OptionDictType]]
         self.base_options = {} # : OptionDictType
         self.cross_files = self.__load_config_files(options, scratch_dir, 'cross')
         self.compilers = PerMachine(OrderedDict(), OrderedDict())
@@ -623,29 +623,41 @@ class CoreData:
         options_per_machine # : PerMachine[T.Dict[str, _V]]]
     ) -> T.Iterable[T.Tuple[str, _V]]:
         return cls._flatten_pair_iterator(
-            (for_machine.get_prefix(), options_per_machine[for_machine])
+            (for_machine.get_prefix(), options_per_machine[for_machine].items())
             for for_machine in iter(MachineChoice)
         )
 
     @classmethod
     def flatten_lang_iterator(
         cls,
-        outer # : T.Iterable[T.Tuple[str, T.Dict[str, _V]]]
+        outer # : T.Iterable[T.Tuple[Language, T.Dict[str, V]]]
     ) -> T.Iterable[T.Tuple[str, _V]]:
-        return cls._flatten_pair_iterator((lang + '_', opts) for lang, opts in outer)
+        return cls._flatten_pair_iterator(
+            (lang.get_lower_case_name() + '_', inner.items())
+            for lang, inner in outer
+        )
+
+    @classmethod
+    def flatten_lang_iterator_per_machine(
+        cls,
+        outer # : PerMachine[Dict[Language, T.Dict[str, V]]]
+    ) -> T.Iterable[T.Tuple[str, _V]]:
+        self.get_prefixed_options_per_machine(
+            self.compiler_options.map(lambda opts_per_lang:
+                self.flatten_lang_iterator(opts_per_lang)))
 
     @staticmethod
     def _flatten_pair_iterator(
-        outer # : T.Iterable[T.Tuple[str, T.Dict[str, _V]]]
+        outer # : T.Iterable[T.Tuple[str, T.Iterable[T.Tuple[str, _V]]]]
     ) -> T.Iterable[T.Tuple[str, _V]]:
         for k0, v0 in outer:
-            for k1, v1 in v0.items():
+            for k1, v1 in v0:
                 yield (k0 + k1, v1)
 
     def _get_all_nonbuiltin_options(self) -> T.Iterable[T.Dict[str, UserOption]]:
         yield self.backend_options
         yield self.user_options
-        yield dict(self.flatten_lang_iterator(self.get_prefixed_options_per_machine(self.compiler_options)))
+        yield dict(flatten_lang_iterator_per_machine(self.compiler_options))
         yield self.base_options
 
     def _get_all_builtin_options(self) -> T.Iterable[T.Dict[str, UserOption]]:
@@ -667,10 +679,10 @@ class CoreData:
                         .with_traceback(sys.exc_info()[2])
         raise MesonException('Tried to validate unknown option %s.' % option_name)
 
-    def get_external_args(self, for_machine: MachineChoice, lang):
+    def get_external_args(self, for_machine: MachineChoice, lang: Language):
         return self.compiler_options[for_machine][lang]['args'].value
 
-    def get_external_link_args(self, for_machine: MachineChoice, lang):
+    def get_external_link_args(self, for_machine: MachineChoice, lang: Language):
         return self.compiler_options[for_machine][lang]['link_args'].value
 
     def merge_user_options(self, options):
@@ -821,7 +833,7 @@ class CoreData:
 
         self.set_options(options, subproject=subproject)
 
-    def add_lang_args(self, lang: str, comp: T.Type['Compiler'],
+    def add_lang_args(self, lang: Language, comp: T.Type['Compiler'],
                       for_machine: MachineChoice, env: 'Environment') -> None:
         """Add global language arguments that are needed before compiler/linker detection."""
         from .compilers import compilers
@@ -834,12 +846,12 @@ class CoreData:
                 env.properties[for_machine]).items():
             # prefixed compiler options affect just this machine
             opt_prefix = for_machine.get_prefix()
-            user_k = opt_prefix + lang + '_' + k
+            user_k = opt_prefix + lang.get_lower_case_name() + '_' + k
             if user_k in env.cmd_line_options:
                 o.set_value(env.cmd_line_options[user_k])
             self.compiler_options[for_machine][lang].setdefault(k, o)
 
-    def process_new_compiler(self, lang: str, comp: T.Type['Compiler'], env: 'Environment') -> None:
+    def process_new_compiler(self, lang: Language, comp: T.Type['Compiler'], env: 'Environment') -> None:
         from . import compilers
 
         self.compilers[comp.for_machine][lang] = comp
@@ -848,7 +860,7 @@ class CoreData:
         for k, o in comp.get_options().items():
             # prefixed compiler options affect just this machine
             opt_prefix = comp.for_machine.get_prefix()
-            user_k = opt_prefix + lang + '_' + k
+            user_k = opt_prefix + lang.get_lower_case_name() + '_' + k
             if user_k in env.cmd_line_options:
                 o.set_value(env.cmd_line_options[user_k])
             self.compiler_options[comp.for_machine][lang].setdefault(k, o)
diff --git a/mesonbuild/envconfig.py b/mesonbuild/envconfig.py
index 25b3c7f..327d3fa 100644
--- a/mesonbuild/envconfig.py
+++ b/mesonbuild/envconfig.py
@@ -152,13 +152,13 @@ class Properties:
         self.properties = properties or {}  # type: T.Dict[str, T.Union[str, T.List[str]]]
 
     def has_stdlib(self, language: str) -> bool:
-        return language + '_stdlib' in self.properties
+        return language.get_lower_case_name() + '_stdlib' in self.properties
 
     # Some of get_stdlib, get_root, get_sys_root are wider than is actually
     # true, but without heterogenious dict annotations it's not practical to
     # narrow them
     def get_stdlib(self, language: str) -> T.Union[str, T.List[str]]:
-        return self.properties[language + '_stdlib']
+        return self.properties[language.get_lower_case_name() + '_stdlib']
 
     def get_root(self) -> T.Optional[T.Union[str, T.List[str]]]:
         return self.properties.get('root', None)
diff --git a/mesonbuild/environment.py b/mesonbuild/environment.py
index 64efda6..18b7773 100644
--- a/mesonbuild/environment.py
+++ b/mesonbuild/environment.py
@@ -21,7 +21,7 @@ from . import coredata
 from .linkers import ArLinker, ArmarLinker, VisualStudioLinker, DLinker, CcrxLinker, Xc16Linker, C2000Linker, IntelVisualStudioLinker
 from . import mesonlib
 from .mesonlib import (
-    MesonException, EnvironmentException, MachineChoice, Popen_safe,
+    MesonException, EnvironmentException, Language, MachineChoice, Popen_safe,
     PerMachineDefaultable, PerThreeMachineDefaultable, split_args, quote_arg
 )
 from . import mlog
@@ -774,7 +774,7 @@ class Environment:
         check_args += self.coredata.compiler_options[for_machine][comp_class.language]['args'].value
 
         override = []  # type: T.List[str]
-        value = self.lookup_binary_entry(for_machine, comp_class.language + '_ld')
+        value = self.lookup_binary_entry(for_machine, comp_class.language.get_lower_case_name() + '_ld')
         if value is not None:
             override = comp_class.use_linker_args(value[0])
             check_args += override
@@ -841,7 +841,7 @@ class Environment:
             check_args = comp_class.LINKER_PREFIX + ['--version'] + extra_args
 
         override = []  # type: T.List[str]
-        value = self.lookup_binary_entry(for_machine, comp_class.language + '_ld')
+        value = self.lookup_binary_entry(for_machine, comp_class.language.get_lower_case_name() + '_ld')
         if value is not None:
             override = comp_class.use_linker_args(value[0])
             check_args += override
@@ -896,7 +896,7 @@ class Environment:
             raise EnvironmentException('Unable to determine dynamic linker')
         return linker
 
-    def _detect_c_or_cpp_compiler(self, lang: str, for_machine: MachineChoice) -> Compiler:
+    def _detect_c_or_cpp_compiler(self, lang: Language, for_machine: MachineChoice) -> Compiler:
         popen_exceptions = {}
         compilers, ccache, exe_wrap = self._get_compilers(lang, for_machine)
         is_cross = not self.machines.matches_build_machine(for_machine)
@@ -1623,7 +1623,7 @@ class Environment:
 
         raise EnvironmentException('Unknown compiler "' + ' '.join(exelist) + '"')
 
-    def compiler_from_language(self, lang: str, for_machine: MachineChoice):
+    def compiler_from_language(self, lang: Language, for_machine: MachineChoice):
         if lang == 'c':
             comp = self.detect_c_compiler(for_machine)
         elif lang == 'cpp':
@@ -1652,7 +1652,7 @@ class Environment:
             comp = None
         return comp
 
-    def detect_compiler_for(self, lang: str, for_machine: MachineChoice):
+    def detect_compiler_for(self, lang: Language, for_machine: MachineChoice):
         comp = self.compiler_from_language(lang, for_machine)
         if comp is not None:
             assert comp.for_machine == for_machine
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 48b6bd6..fb606ca 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2802,8 +2802,7 @@ external dependencies (including libraries) must go to "dependencies".''')
         for opts in [
                 self.coredata.base_options, compilers.base_options, self.coredata.builtins,
                 dict(self.coredata.get_prefixed_options_per_machine(self.coredata.builtins_per_machine)),
-                dict(self.coredata.flatten_lang_iterator(
-                    self.coredata.get_prefixed_options_per_machine(self.coredata.compiler_options))),
+                dict(self.coredata.flatten_lang_iterator_per_machine(self.coredata.compiler_options)),
         ]:
             v = opts.get(optname)
             if v is None or v.yielding:
diff --git a/mesonbuild/mconf.py b/mesonbuild/mconf.py
index 05e9518..6c450da 100644
--- a/mesonbuild/mconf.py
+++ b/mesonbuild/mconf.py
@@ -216,9 +216,9 @@ class Conf:
             self.coredata.flatten_lang_iterator(
                 self.coredata.compiler_options.host.items()))
         build_compiler_options = self.split_options_per_subproject(
-            self.coredata.flatten_lang_iterator(
-                (insert_build_prefix(k), o)
-                for k, o in self.coredata.compiler_options.build.items()))
+            (insert_build_prefix(k), o)
+            for k, o in self.coredata.flatten_lang_iterator(
+                self.coredata.compiler_options.build.items()))
         project_options = self.split_options_per_subproject(self.coredata.user_options.items())
         show_build_options = self.default_values_only or self.build.environment.is_cross_build()
 
diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index 6c1e466..0ce3df1 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -14,6 +14,7 @@
 
 """A library of random helper functionality."""
 from pathlib import Path
+import copy
 import sys
 import stat
 import time
@@ -373,6 +374,12 @@ class PerMachine(T.Generic[_T]):
     def __setitem__(self, machine: MachineChoice, val: _T) -> None:
         setattr(self, machine.get_lower_case_name(), val)
 
+    def map(self, fun):
+        return PerMachine(
+            fun(self.build),
+            fun(self.host),
+        )
+
     def miss_defaulting(self) -> "PerMachineDefaultable[T.Optional[_T]]":
         """Unset definition duplicated from their previous to None
 
@@ -459,6 +466,59 @@ class PerThreeMachineDefaultable(PerMachineDefaultable, PerThreeMachine[T.Option
         return freeze
 
 
+class Language(Enum):
+
+    """Enum class representing the languages Meson supports.
+    """
+
+    # Alphabetized for now, but order comparisons explicitly disallowed so it
+    # shouldn't matter.
+    C = 0
+    CPP = 1
+    CS = 2
+    CUDA = 3
+    D = 4
+    FORTRAN = 5
+    JAVA = 6
+    OBJC = 7
+    OBJCPP = 8
+    RUST = 9
+    SWIFT = 10
+    VALA = 11
+
+    def get_lower_case_name(self) -> str:
+        return {
+            Language.C: 'c',
+            Language.CPP: 'cpp',
+            Language.CS: 'cs',
+            Language.CUDA: 'cuda',
+            Language.D: 'd',
+            Language.FORTRAN: 'fortran',
+            Language.JAVA: 'java',
+            Language.OBJC: 'objc',
+            Language.OBJCPP: 'objcpp',
+            Language.RUST: 'rust',
+            Language.SWIFT: 'swift',
+            Language.VALA: 'vala',
+        }[self]
+
+    @staticmethod
+    def from_lower_case_name(lang_name: str) -> Language:
+        return {
+            'c': Language.C,
+            'cpp': Language.CPP,
+            'cs': Language.CS,
+            'cuda': Language.CUDA,
+            'd': Language.D,
+            'fortran': Language.FORTRAN,
+            'java': Language.JAVA,
+            'objc': Language.OBJC,
+            'objcpp': Language.OBJCPP,
+            'rust': Language.RUST,
+            'swift': Language.SWIFT,
+            'vala': Language.VALA,
+        }[lang_name]
+
 def is_sunos() -> bool:
     return platform.system().lower() == 'sunos'
 
diff --git a/mesonbuild/optinterpreter.py b/mesonbuild/optinterpreter.py
index c13cc5d..c3cf1d8 100644
--- a/mesonbuild/optinterpreter.py
+++ b/mesonbuild/optinterpreter.py
@@ -22,7 +22,7 @@ from . import mesonlib
 from . import compilers
 
 forbidden_option_names = set(coredata.builtin_options.keys())
-forbidden_prefixes = [lang + '_' for lang in compilers.all_languages] + ['b_', 'backend_']
+forbidden_prefixes = [lang.get_lower_case_name() + '_' for lang in compilers.all_languages] + ['b_', 'backend_']
 reserved_prefixes = ['cross_']
 
 def is_invalid_name(name: str, *, log: bool = True) -> bool:
diff --git a/run_unittests.py b/run_unittests.py
index 831e53f..e427ee9 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -53,7 +53,7 @@ import mesonbuild.modules.gnome
 from mesonbuild.interpreter import Interpreter, ObjectHolder
 from mesonbuild.ast import AstInterpreter
 from mesonbuild.mesonlib import (
-    BuildDirLock, LibType, MachineChoice, PerMachine, Version, is_windows,
+    BuildDirLock, Language, LibType, MachineChoice, PerMachine, Version, is_windows,
     is_osx, is_cygwin, is_dragonflybsd, is_openbsd, is_haiku, is_sunos,
     windows_proof_rmtree, python_command, version_compare, split_args,
     quote_arg, relpath