compilers: avoid importing compilers upfront for detect

We no longer need these upfront at all, since we now import the ones we
need for the language we are detecting, at the time of actual detection.

This avoids importing 28 files, consisting of just under 9,000 lines of
code, at interpreter startup. Now, it is only imported depending on
which languages are invoked by add_languages, which may not even be
anything. And even if we do end up importing a fair chunk of it for
C/C++ projects, spreading the import cost around the interpreter runtime
helps responsiveness.

mesonbuild/compilers/detect.py

@@ -20,118 +20,7 @@ from ..mesonlib import (
 from ..envconfig import BinaryTable
 from .. import mlog
 
-from ..linkers import (
+from ..linkers import guess_win_linker, guess_nix_linker
-    guess_win_linker,
-    guess_nix_linker,
-    AIXArLinker,
-    AppleArLinker,
-    ArLinker,
-    ArmarLinker,
-    ArmClangDynamicLinker,
-    ArmDynamicLinker,
-    CcrxLinker,
-    CcrxDynamicLinker,
-    CompCertLinker,
-    CompCertDynamicLinker,
-    C2000Linker,
-    C2000DynamicLinker,
-    TILinker,
-    TIDynamicLinker,
-    DLinker,
-    NAGDynamicLinker,
-    NvidiaHPC_DynamicLinker,
-    PGIDynamicLinker,
-    PGIStaticLinker,
-    Xc16Linker,
-    Xc16DynamicLinker,
-    XilinkDynamicLinker,
-    CudaLinker,
-    IntelVisualStudioLinker,
-    VisualStudioLinker,
-    VisualStudioLikeLinkerMixin,
-    WASMDynamicLinker,
-)
-from .c import (
-    AppleClangCCompiler,
-    ArmCCompiler,
-    ArmclangCCompiler,
-    ArmLtdClangCCompiler,
-    ClangCCompiler,
-    ClangClCCompiler,
-    GnuCCompiler,
-    ElbrusCCompiler,
-    EmscriptenCCompiler,
-    IntelCCompiler,
-    IntelClCCompiler,
-    NvidiaHPC_CCompiler,
-    PGICCompiler,
-    CcrxCCompiler,
-    Xc16CCompiler,
-    CompCertCCompiler,
-    C2000CCompiler,
-    TICCompiler,
-    VisualStudioCCompiler,
-)
-from .cpp import (
-    AppleClangCPPCompiler,
-    ArmCPPCompiler,
-    ArmclangCPPCompiler,
-    ArmLtdClangCPPCompiler,
-    ClangCPPCompiler,
-    ClangClCPPCompiler,
-    GnuCPPCompiler,
-    ElbrusCPPCompiler,
-    EmscriptenCPPCompiler,
-    IntelCPPCompiler,
-    IntelClCPPCompiler,
-    NvidiaHPC_CPPCompiler,
-    PGICPPCompiler,
-    CcrxCPPCompiler,
-    C2000CPPCompiler,
-    TICPPCompiler,
-    VisualStudioCPPCompiler,
-)
-from .cs import MonoCompiler, VisualStudioCsCompiler
-from .d import (
-    DCompiler,
-    DmdDCompiler,
-    GnuDCompiler,
-    LLVMDCompiler,
-)
-from .cuda import CudaCompiler
-from .fortran import (
-    ArmLtdFlangFortranCompiler,
-    G95FortranCompiler,
-    GnuFortranCompiler,
-    ElbrusFortranCompiler,
-    FlangFortranCompiler,
-    IntelFortranCompiler,
-    IntelClFortranCompiler,
-    NAGFortranCompiler,
-    Open64FortranCompiler,
-    PathScaleFortranCompiler,
-    NvidiaHPC_FortranCompiler,
-    PGIFortranCompiler,
-    SunFortranCompiler,
-)
-from .java import JavaCompiler
-from .objc import (
-    AppleClangObjCCompiler,
-    ClangObjCCompiler,
-    GnuObjCCompiler,
-)
-from .objcpp import (
-    AppleClangObjCPPCompiler,
-    ClangObjCPPCompiler,
-    GnuObjCPPCompiler,
-)
-from .cython import CythonCompiler
-from .rust import RustCompiler, ClippyRustCompiler
-from .swift import SwiftCompiler
-from .vala import ValaCompiler
-from .mixins.visualstudio import VisualStudioLikeCompiler
-from .mixins.gnu import GnuCompiler
-from .mixins.clang import ClangCompiler
 
 import subprocess
 import platform
@@ -146,8 +35,7 @@ if T.TYPE_CHECKING:
     from .c import CCompiler
     from .cpp import CPPCompiler
     from .fortran import FortranCompiler
-    from .objc import ObjCCompiler
+    from .rust import RustCompiler
-    from .objcpp import ObjCPPCompiler
     from ..linkers import StaticLinker
     from ..environment import Environment
     from ..programs import ExternalProgram