Add warning_level=everything

Adds a new maximum warning level that is roughly equivalent to "all warnings".
This adds a way to use `/Wall` with MSVC (without the previous broken warning),
`-Weverything` with clang, and almost all general warnings in GCC with
strictness roughly equivalent to clang's `-Weverything`.

The GCC case must be implemented by meson since GCC doesn't provide a similar
option.  To avoid maintenance headaches for meson, this warning level is
defined objectively: all warnings are included except those that require
specific values or are specific to particular language revisions.  This warning
level is mainly intended for new code, and it is expected (nearly guaranteed)
that projects will need to add some suppressions to build cleanly with it.

More commonly, it's just a handy way to occasionally take a look at what
warnings are present with some compiler, in case anything interesting shows up
you might want to enable in general.

Since the warnings enabled at this level are inherently unstable with respect
to compiler versions, it is intended for use by developers and not to be set as
the default.

20 files changed, 335 insertions, 43 deletions

diff --git a/docs/markdown/Builtin-options.md b/docs/markdown/Builtin-options.md
index 22627f4..4c43f09 100644
--- a/docs/markdown/Builtin-options.md
+++ b/docs/markdown/Builtin-options.md
@@ -85,7 +85,7 @@ machine](#specifying-options-per-machine) section for details.
 | strip                                  | false         | Strip targets on install                                       | no             | no                |
 | unity {on, off, subprojects}           | off           | Unity build                                                    | no             | no                |
 | unity_size {>=2}                       | 4             | Unity file block size                                          | no             | no                |
-| warning_level {0, 1, 2, 3}             | 1             | Set the warning level. From 0 = none to 3 = highest            | no             | yes               |
+| warning_level {0, 1, 2, 3, everything} | 1             | Set the warning level. From 0 = none to everything = highest   | no             | yes               |
 | werror                                 | false         | Treat warnings as errors                                       | no             | yes               |
 | wrap_mode {default, nofallback,<br>nodownload, forcefallback, nopromote} | default | Wrap mode to use                 | no             | no                |
 | force_fallback_for                     | []            | Force fallback for those dependencies                          | no             | no                |
diff --git a/docs/markdown/Configuring-a-build-directory.md b/docs/markdown/Configuring-a-build-directory.md
index 2012b37..6b9bb40 100644
--- a/docs/markdown/Configuring-a-build-directory.md
+++ b/docs/markdown/Configuring-a-build-directory.md
@@ -34,7 +34,7 @@ a sample output for a simple project.
       prefer_static   false         [true, false]                                              Whether to try static linking before shared linking
       strip           false         [true, false]                                              Strip targets on install
       unity           off           [on, off, subprojects]                                     Unity build
-      warning_level   1             [0, 1, 2, 3]                                               Compiler warning level to use
+      warning_level   1             [0, 1, 2, 3, everything]                                   Compiler warning level to use
       werror          false         [true, false]                                              Treat warnings as errors
 
     Backend options:
diff --git a/docs/markdown/snippets/warning_level_everything.md b/docs/markdown/snippets/warning_level_everything.md
new file mode 100644
index 0000000..5558cf5
--- /dev/null
+++ b/docs/markdown/snippets/warning_level_everything.md
@@ -0,0 +1,5 @@
+## `warning-level=everything` option
+
+The new `everything` value for the built-in `warning_level` enables roughly all applicable compiler warnings.
+For clang and MSVC, this simply enables `-Weverything` or `/Wall`, respectively.
+For GCC, meson enables warnings approximately equivalent to `-Weverything` from clang.
diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index 0b78442..51ae246 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -28,6 +28,7 @@ from .mixins.ti import TICompiler
 from .mixins.arm import ArmCompiler, ArmclangCompiler
 from .mixins.visualstudio import MSVCCompiler, ClangClCompiler
 from .mixins.gnu import GnuCompiler
+from .mixins.gnu import gnu_common_warning_args, gnu_c_warning_args
 from .mixins.intel import IntelGnuLikeCompiler, IntelVisualStudioLikeCompiler
 from .mixins.clang import ClangCompiler
 from .mixins.elbrus import ElbrusCompiler
@@ -152,7 +153,8 @@ class ClangCCompiler(_ClangCStds, ClangCompiler, CCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': ['-Weverything']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = super().get_options()
@@ -233,7 +235,8 @@ class ArmclangCCompiler(ArmclangCompiler, CCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': ['-Weverything']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CCompiler.get_options(self)
@@ -271,7 +274,10 @@ class GnuCCompiler(GnuCompiler, CCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': (default_warn_args + ['-Wextra', '-Wpedantic'] +
+                                         self.supported_warn_args(gnu_common_warning_args) +
+                                         self.supported_warn_args(gnu_c_warning_args))}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CCompiler.get_options(self)
@@ -385,11 +391,12 @@ class IntelCCompiler(IntelGnuLikeCompiler, CCompiler):
                            info, exe_wrapper, linker=linker, full_version=full_version)
         IntelGnuLikeCompiler.__init__(self)
         self.lang_header = 'c-header'
-        default_warn_args = ['-Wall', '-w3', '-diag-disable:remark']
+        default_warn_args = ['-Wall', '-w3']
         self.warn_args = {'0': [],
-                          '1': default_warn_args,
-                          '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra']}
+                          '1': default_warn_args + ['-diag-disable:remark'],
+                          '2': default_warn_args + ['-Wextra', '-diag-disable:remark'],
+                          '3': default_warn_args + ['-Wextra', '-diag-disable:remark'],
+                          'everything': default_warn_args + ['-Wextra']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CCompiler.get_options(self)
diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index 1ea9bca..7e1cc54 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -33,7 +33,7 @@ from .mixins.ccrx import CcrxCompiler
 from .mixins.ti import TICompiler
 from .mixins.arm import ArmCompiler, ArmclangCompiler
 from .mixins.visualstudio import MSVCCompiler, ClangClCompiler
-from .mixins.gnu import GnuCompiler
+from .mixins.gnu import GnuCompiler, gnu_common_warning_args, gnu_cpp_warning_args
 from .mixins.intel import IntelGnuLikeCompiler, IntelVisualStudioLikeCompiler
 from .mixins.clang import ClangCompiler
 from .mixins.elbrus import ElbrusCompiler
@@ -194,7 +194,8 @@ class ClangCPPCompiler(ClangCompiler, CPPCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': ['-Weverything']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CPPCompiler.get_options(self)
@@ -314,7 +315,8 @@ class ArmclangCPPCompiler(ArmclangCompiler, CPPCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': ['-Weverything']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CPPCompiler.get_options(self)
@@ -360,7 +362,10 @@ class GnuCPPCompiler(GnuCompiler, CPPCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': (default_warn_args + ['-Wextra', '-Wpedantic'] +
+                                         self.supported_warn_args(gnu_common_warning_args) +
+                                         self.supported_warn_args(gnu_cpp_warning_args))}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         key = OptionKey('std', machine=self.for_machine, lang=self.language)
@@ -535,12 +540,12 @@ class IntelCPPCompiler(IntelGnuLikeCompiler, CPPCompiler):
                              info, exe_wrapper, linker=linker, full_version=full_version)
         IntelGnuLikeCompiler.__init__(self)
         self.lang_header = 'c++-header'
-        default_warn_args = ['-Wall', '-w3', '-diag-disable:remark',
-                             '-Wpch-messages']
+        default_warn_args = ['-Wall', '-w3', '-Wpch-messages']
         self.warn_args = {'0': [],
-                          '1': default_warn_args,
-                          '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra']}
+                          '1': default_warn_args + ['-diag-disable:remark'],
+                          '2': default_warn_args + ['-Wextra', '-diag-disable:remark'],
+                          '3': default_warn_args + ['-Wextra', '-diag-disable:remark'],
+                          'everything': default_warn_args + ['-Wextra']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = CPPCompiler.get_options(self)
diff --git a/mesonbuild/compilers/d.py b/mesonbuild/compilers/d.py
index b03495c..c7e3b77 100644
--- a/mesonbuild/compilers/d.py
+++ b/mesonbuild/compilers/d.py
@@ -36,6 +36,7 @@ from .compilers import (
     CompileCheckMode,
 )
 from .mixins.gnu import GnuCompiler
+from .mixins.gnu import gnu_common_warning_args
 
 if T.TYPE_CHECKING:
     from ..dependencies import Dependency
@@ -805,7 +806,10 @@ class GnuDCompiler(GnuCompiler, DCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': (default_warn_args + ['-Wextra', '-Wpedantic'] +
+                                         self.supported_warn_args(gnu_common_warning_args))}
+
         self.base_options = {
             OptionKey(o) for o in [
              'b_colorout', 'b_sanitize', 'b_staticpic', 'b_vscrt',
diff --git a/mesonbuild/compilers/fortran.py b/mesonbuild/compilers/fortran.py
index 3f388cf..b82b2ff 100644
--- a/mesonbuild/compilers/fortran.py
+++ b/mesonbuild/compilers/fortran.py
@@ -23,7 +23,7 @@ from .compilers import (
 )
 from .mixins.clike import CLikeCompiler
 from .mixins.gnu import (
-    GnuCompiler, gnulike_buildtype_args, gnu_optimization_args,
+    GnuCompiler, gnulike_buildtype_args, gnu_optimization_args
 )
 from .mixins.intel import IntelGnuLikeCompiler, IntelVisualStudioLikeCompiler
 from .mixins.clang import ClangCompiler
@@ -155,7 +155,8 @@ class GnuFortranCompiler(GnuCompiler, FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic', '-fimplicit-none']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic', '-fimplicit-none'],
+                          'everything': default_warn_args + ['-Wextra', '-Wpedantic', '-fimplicit-none']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = FortranCompiler.get_options(self)
@@ -246,7 +247,8 @@ class G95FortranCompiler(FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-pedantic']}
+                          '3': default_warn_args + ['-Wextra', '-pedantic'],
+                          'everything': default_warn_args + ['-Wextra', '-pedantic']}
 
     def get_module_outdir_args(self, path: str) -> T.List[str]:
         return ['-fmod=' + path]
@@ -299,7 +301,8 @@ class IntelFortranCompiler(IntelGnuLikeCompiler, FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-warn', 'unused'],
-                          '3': ['-warn', 'all']}
+                          '3': ['-warn', 'all'],
+                          'everything': ['-warn', 'all']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = FortranCompiler.get_options(self)
@@ -351,7 +354,8 @@ class IntelClFortranCompiler(IntelVisualStudioLikeCompiler, FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['/warn:unused'],
-                          '3': ['/warn:all']}
+                          '3': ['/warn:all'],
+                          'everything': ['/warn:all']}
 
     def get_options(self) -> 'MutableKeyedOptionDictType':
         opts = FortranCompiler.get_options(self)
@@ -391,7 +395,8 @@ class PathScaleFortranCompiler(FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args,
-                          '3': default_warn_args}
+                          '3': default_warn_args,
+                          'everything': default_warn_args}
 
     def openmp_flags(self) -> T.List[str]:
         return ['-mp']
@@ -412,7 +417,8 @@ class PGIFortranCompiler(PGICompiler, FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args,
-                          '3': default_warn_args + ['-Mdclchk']}
+                          '3': default_warn_args + ['-Mdclchk'],
+                          'everything': default_warn_args + ['-Mdclchk']}
 
     def language_stdlib_only_link_flags(self, env: 'Environment') -> T.List[str]:
         # TODO: needs default search path added
@@ -437,7 +443,8 @@ class NvidiaHPC_FortranCompiler(PGICompiler, FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args,
-                          '3': default_warn_args + ['-Mdclchk']}
+                          '3': default_warn_args + ['-Mdclchk'],
+                          'everything': default_warn_args + ['-Mdclchk']}
 
 
 class FlangFortranCompiler(ClangCompiler, FortranCompiler):
@@ -456,7 +463,8 @@ class FlangFortranCompiler(ClangCompiler, FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args,
-                          '3': default_warn_args}
+                          '3': default_warn_args,
+                          'everything': default_warn_args}
 
     def language_stdlib_only_link_flags(self, env: 'Environment') -> T.List[str]:
         # We need to apply the search prefix here, as these link arguments may
@@ -488,7 +496,8 @@ class Open64FortranCompiler(FortranCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args,
-                          '3': default_warn_args}
+                          '3': default_warn_args,
+                          'everything': default_warn_args}
 
     def openmp_flags(self) -> T.List[str]:
         return ['-mp']
@@ -511,6 +520,7 @@ class NAGFortranCompiler(FortranCompiler):
             '1': [],
             '2': [],
             '3': [],
+            'everything': [],
         }
 
     def get_always_args(self) -> T.List[str]:
diff --git a/mesonbuild/compilers/mixins/arm.py b/mesonbuild/compilers/mixins/arm.py
index b3abd70..f0cbf59 100644
--- a/mesonbuild/compilers/mixins/arm.py
+++ b/mesonbuild/compilers/mixins/arm.py
@@ -85,7 +85,8 @@ class ArmCompiler(Compiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + [],
-                          '3': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
+                          '3': default_warn_args + [],
+                          'everything': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
         # Assembly
         self.can_compile_suffixes.add('s')
 
diff --git a/mesonbuild/compilers/mixins/ccrx.py b/mesonbuild/compilers/mixins/ccrx.py
index f4c5e06..1c22214 100644
--- a/mesonbuild/compilers/mixins/ccrx.py
+++ b/mesonbuild/compilers/mixins/ccrx.py
@@ -72,7 +72,8 @@ class CcrxCompiler(Compiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + [],
-                          '3': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
+                          '3': default_warn_args + [],
+                          'everything': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
 
     def get_pic_args(self) -> T.List[str]:
         # PIC support is not enabled by default for CCRX,
diff --git a/mesonbuild/compilers/mixins/compcert.py b/mesonbuild/compilers/mixins/compcert.py
index f4f4cdb..a0394a9 100644
--- a/mesonbuild/compilers/mixins/compcert.py
+++ b/mesonbuild/compilers/mixins/compcert.py
@@ -72,7 +72,8 @@ class CompCertCompiler(Compiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + [],
-                          '3': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
+                          '3': default_warn_args + [],
+                          'everything': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
 
     def get_always_args(self) -> T.List[str]:
         return []
diff --git a/mesonbuild/compilers/mixins/elbrus.py b/mesonbuild/compilers/mixins/elbrus.py
index 4cab777..7362039 100644
--- a/mesonbuild/compilers/mixins/elbrus.py
+++ b/mesonbuild/compilers/mixins/elbrus.py
@@ -41,7 +41,8 @@ class ElbrusCompiler(GnuLikeCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': default_warn_args + ['-Wextra', '-Wpedantic']}
 
     # FIXME: use _build_wrapper to call this so that linker flags from the env
     # get applied
diff --git a/mesonbuild/compilers/mixins/gnu.py b/mesonbuild/compilers/mixins/gnu.py
index 552c559..8152b25 100644
--- a/mesonbuild/compilers/mixins/gnu.py
+++ b/mesonbuild/compilers/mixins/gnu.py
@@ -92,6 +92,238 @@ gnu_color_args = {
     'never': ['-fdiagnostics-color=never'],
 }  # type: T.Dict[str, T.List[str]]
 
+# Warnings collected from the GCC source and documentation.  This is an
+# objective set of all the warnings flags that apply to general projects: the
+# only ones omitted are those that require a project-specific value, or are
+# related to non-standard or legacy language support.  This behaves roughly
+# like -Weverything in clang.  Warnings implied by -Wall, -Wextra, or
+# higher-level warnings already enabled here are not included in these lists to
+# keep them as short as possible.  History goes back to GCC 3.0.0, everything
+# earlier is considered historical and listed under version 0.0.0.
+
+# GCC warnings for all C-family languages
+# Omitted non-general warnings:
+#   -Wabi=
+#   -Waggregate-return
+#   -Walloc-size-larger-than=BYTES
+#   -Walloca-larger-than=BYTES
+#   -Wframe-larger-than=BYTES
+#   -Wlarger-than=BYTES
+#   -Wstack-usage=BYTES
+#   -Wsystem-headers
+#   -Wtrampolines
+#   -Wvla-larger-than=BYTES
+#
+# Omitted warnings enabled elsewhere in meson:
+#   -Winvalid-pch (GCC 3.4.0)
+gnu_common_warning_args = {
+    "0.0.0": [
+        "-Wcast-qual",
+        "-Wconversion",
+        "-Wfloat-equal",
+        "-Wformat=2",
+        "-Winline",
+        "-Wmissing-declarations",
+        "-Wredundant-decls",
+        "-Wshadow",
+        "-Wundef",
+        "-Wuninitialized",
+        "-Wwrite-strings",
+    ],
+    "3.0.0": [
+        "-Wdisabled-optimization",
+        "-Wpacked",
+        "-Wpadded",
+    ],
+    "3.3.0": [
+        "-Wmultichar",
+        "-Wswitch-default",
+        "-Wswitch-enum",
+        "-Wunused-macros",
+    ],
+    "4.0.0": [
+        "-Wmissing-include-dirs",
+    ],
+    "4.1.0": [
+        "-Wunsafe-loop-optimizations",
+        "-Wstack-protector",
+    ],
+    "4.2.0": [
+        "-Wstrict-overflow=5",
+    ],
+    "4.3.0": [
+        "-Warray-bounds=2",
+        "-Wlogical-op",
+        "-Wstrict-aliasing=3",
+        "-Wvla",
+    ],
+    "4.6.0": [
+        "-Wdouble-promotion",
+        "-Wsuggest-attribute=const",
+        "-Wsuggest-attribute=noreturn",
+        "-Wsuggest-attribute=pure",
+        "-Wtrampolines",
+    ],
+    "4.7.0": [
+        "-Wvector-operation-performance",
+    ],
+    "4.8.0": [
+        "-Wsuggest-attribute=format",
+    ],
+    "4.9.0": [
+        "-Wdate-time",
+    ],
+    "5.1.0": [
+        "-Wformat-signedness",
+        "-Wnormalized=nfc",
+    ],
+    "6.1.0": [
+        "-Wduplicated-cond",
+        "-Wnull-dereference",
+        "-Wshift-negative-value",
+        "-Wshift-overflow=2",
+        "-Wunused-const-variable=2",
+    ],
+    "7.1.0": [
+        "-Walloca",
+        "-Walloc-zero",
+        "-Wformat-overflow=2",
+        "-Wformat-truncation=2",
+        "-Wstringop-overflow=3",
+    ],
+    "7.2.0": [
+        "-Wduplicated-branches",
+    ],
+    "8.1.0": [
+        "-Wattribute-alias=2",
+        "-Wcast-align=strict",
+        "-Wsuggest-attribute=cold",
+        "-Wsuggest-attribute=malloc",
+    ],
+    "10.1.0": [
+        "-Wanalyzer-too-complex",
+        "-Warith-conversion",
+    ],
+    "12.1.0": [
+        "-Wbidi-chars=ucn",
+        "-Wopenacc-parallelism",
+        "-Wtrivial-auto-var-init",
+    ],
+}  # type: T.Dict[str, T.List[str]]
+
+# GCC warnings for C
+# Omitted non-general or legacy warnings:
+#   -Wc11-c2x-compat
+#   -Wc90-c99-compat
+#   -Wc99-c11-compat
+#   -Wdeclaration-after-statement
+#   -Wtraditional
+#   -Wtraditional-conversion
+gnu_c_warning_args = {
+    "0.0.0": [
+        "-Wbad-function-cast",
+        "-Wmissing-prototypes",
+        "-Wnested-externs",
+        "-Wstrict-prototypes",
+    ],
+    "3.4.0": [
+        "-Wold-style-definition",
+        "-Winit-self",
+    ],
+    "4.1.0": [
+        "-Wc++-compat",
+    ],
+    "4.5.0": [
+        "-Wunsuffixed-float-constants",
+    ],
+}  # type: T.Dict[str, T.List[str]]
+
+# GCC warnings for C++
+# Omitted non-general or legacy warnings:
+#   -Wc++0x-compat
+#   -Wc++1z-compat
+#   -Wc++2a-compat
+#   -Wctad-maybe-unsupported
+#   -Wnamespaces
+#   -Wtemplates
+gnu_cpp_warning_args = {
+    "0.0.0": [
+        "-Wctor-dtor-privacy",
+        "-Weffc++",
+        "-Wnon-virtual-dtor",
+        "-Wold-style-cast",
+        "-Woverloaded-virtual",
+        "-Wsign-promo",
+    ],
+    "4.0.1": [
+        "-Wstrict-null-sentinel",
+    ],
+    "4.6.0": [
+        "-Wnoexcept",
+    ],
+    "4.7.0": [
+        "-Wzero-as-null-pointer-constant",
+    ],
+    "4.8.0": [
+        "-Wabi-tag",
+        "-Wuseless-cast",
+    ],
+    "4.9.0": [
+        "-Wconditionally-supported",
+    ],
+    "5.1.0": [
+        "-Wsuggest-final-methods",
+        "-Wsuggest-final-types",
+        "-Wsuggest-override",
+    ],
+    "6.1.0": [
+        "-Wmultiple-inheritance",
+        "-Wplacement-new=2",
+        "-Wvirtual-inheritance",
+    ],
+    "7.1.0": [
+        "-Waligned-new=all",
+        "-Wnoexcept-type",
+        "-Wregister",
+    ],
+    "8.1.0": [
+        "-Wcatch-value=3",
+        "-Wextra-semi",
+    ],
+    "9.1.0": [
+        "-Wdeprecated-copy-dtor",
+        "-Wredundant-move",
+    ],
+    "10.1.0": [
+        "-Wcomma-subscript",
+        "-Wmismatched-tags",
+        "-Wredundant-tags",
+        "-Wvolatile",
+    ],
+    "11.1.0": [
+        "-Wdeprecated-enum-enum-conversion",
+        "-Wdeprecated-enum-float-conversion",
+        "-Winvalid-imported-macros",
+    ],
+}  # type: T.Dict[str, T.List[str]]
+
+# GCC warnings for Objective C and Objective C++
+# Omitted non-general or legacy warnings:
+#   -Wtraditional
+#   -Wtraditional-conversion
+gnu_objc_warning_args = {
+    "0.0.0": [
+        "-Wselector",
+    ],
+    "3.3": [
+        "-Wundeclared-selector",
+    ],
+    "4.1.0": [
+        "-Wassign-intercept",
+        "-Wstrict-selector-match",
+    ],
+}  # type: T.Dict[str, T.List[str]]
+
 
 @functools.lru_cache(maxsize=None)
 def gnulike_default_include_dirs(compiler: T.Tuple[str, ...], lang: str) -> 'ImmutableListProtocol[str]':
@@ -351,6 +583,13 @@ class GnuCompiler(GnuLikeCompiler):
             args[args.index('-Wpedantic')] = '-pedantic'
         return args
 
+    def supported_warn_args(self, warn_args_by_version: T.Dict[str, T.List[str]]) -> T.List[str]:
+        result = []
+        for version, warn_args in warn_args_by_version.items():
+            if mesonlib.version_compare(self.version, '>=' + version):
+                result += warn_args
+        return result
+
     def has_builtin_define(self, define: str) -> bool:
         return define in self.defines
 
diff --git a/mesonbuild/compilers/mixins/pgi.py b/mesonbuild/compilers/mixins/pgi.py
index d13e946..212d130 100644
--- a/mesonbuild/compilers/mixins/pgi.py
+++ b/mesonbuild/compilers/mixins/pgi.py
@@ -53,7 +53,8 @@ class PGICompiler(Compiler):
             '0': [],
             '1': default_warn_args,
             '2': default_warn_args,
-            '3': default_warn_args
+            '3': default_warn_args,
+            'everything': default_warn_args
         }
 
     def get_module_incdir_args(self) -> T.Tuple[str]:
diff --git a/mesonbuild/compilers/mixins/ti.py b/mesonbuild/compilers/mixins/ti.py
index 1821b2a..950c97f 100644
--- a/mesonbuild/compilers/mixins/ti.py
+++ b/mesonbuild/compilers/mixins/ti.py
@@ -71,7 +71,8 @@ class TICompiler(Compiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + [],
-                          '3': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
+                          '3': default_warn_args + [],
+                          'everything': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
 
     def get_pic_args(self) -> T.List[str]:
         # PIC support is not enabled by default for TI compilers,
diff --git a/mesonbuild/compilers/mixins/visualstudio.py b/mesonbuild/compilers/mixins/visualstudio.py
index 76ce9c1..d61ad42 100644
--- a/mesonbuild/compilers/mixins/visualstudio.py
+++ b/mesonbuild/compilers/mixins/visualstudio.py
@@ -110,6 +110,7 @@ class VisualStudioLikeCompiler(Compiler, metaclass=abc.ABCMeta):
         '1': ['/W2'],
         '2': ['/W3'],
         '3': ['/W4'],
+        'everything': ['/Wall'],
     }  # type: T.Dict[str, T.List[str]]
 
     INVOKES_LINKER = False
diff --git a/mesonbuild/compilers/mixins/xc16.py b/mesonbuild/compilers/mixins/xc16.py
index f160b34..09949a2 100644
--- a/mesonbuild/compilers/mixins/xc16.py
+++ b/mesonbuild/compilers/mixins/xc16.py
@@ -69,7 +69,8 @@ class Xc16Compiler(Compiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + [],
-                          '3': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
+                          '3': default_warn_args + [],
+                          'everything': default_warn_args + []}  # type: T.Dict[str, T.List[str]]
 
     def get_always_args(self) -> T.List[str]:
         return []
diff --git a/mesonbuild/compilers/objc.py b/mesonbuild/compilers/objc.py
index fc82e15..83dcaad 100644
--- a/mesonbuild/compilers/objc.py
+++ b/mesonbuild/compilers/objc.py
@@ -20,7 +20,7 @@ from ..mesonlib import OptionKey
 
 from .compilers import Compiler
 from .mixins.clike import CLikeCompiler
-from .mixins.gnu import GnuCompiler
+from .mixins.gnu import GnuCompiler, gnu_common_warning_args, gnu_objc_warning_args
 from .mixins.clang import ClangCompiler
 
 if T.TYPE_CHECKING:
@@ -68,7 +68,10 @@ class GnuObjCCompiler(GnuCompiler, ObjCCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': (default_warn_args + ['-Wextra', '-Wpedantic'] +
+                                         self.supported_warn_args(gnu_common_warning_args) +
+                                         self.supported_warn_args(gnu_objc_warning_args))}
 
 
 class ClangObjCCompiler(ClangCompiler, ObjCCompiler):
@@ -85,7 +88,8 @@ class ClangObjCCompiler(ClangCompiler, ObjCCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': ['-Weverything']}
 
     def get_options(self) -> 'coredata.MutableKeyedOptionDictType':
         opts = super().get_options()
diff --git a/mesonbuild/compilers/objcpp.py b/mesonbuild/compilers/objcpp.py
index f44931f..1f9f756 100644
--- a/mesonbuild/compilers/objcpp.py
+++ b/mesonbuild/compilers/objcpp.py
@@ -20,7 +20,7 @@ from ..mesonlib import OptionKey
 
 from .mixins.clike import CLikeCompiler
 from .compilers import Compiler
-from .mixins.gnu import GnuCompiler
+from .mixins.gnu import GnuCompiler, gnu_common_warning_args, gnu_objc_warning_args
 from .mixins.clang import ClangCompiler
 
 if T.TYPE_CHECKING:
@@ -67,7 +67,10 @@ class GnuObjCPPCompiler(GnuCompiler, ObjCPPCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': (default_warn_args + ['-Wextra', '-Wpedantic'] +
+                                         self.supported_warn_args(gnu_common_warning_args) +
+                                         self.supported_warn_args(gnu_objc_warning_args))}
 
 
 class ClangObjCPPCompiler(ClangCompiler, ObjCPPCompiler):
@@ -85,7 +88,8 @@ class ClangObjCPPCompiler(ClangCompiler, ObjCPPCompiler):
         self.warn_args = {'0': [],
                           '1': default_warn_args,
                           '2': default_warn_args + ['-Wextra'],
-                          '3': default_warn_args + ['-Wextra', '-Wpedantic']}
+                          '3': default_warn_args + ['-Wextra', '-Wpedantic'],
+                          'everything': ['-Weverything']}
 
     def get_options(self) -> 'coredata.MutableKeyedOptionDictType':
         opts = super().get_options()
diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index e94c02a..d94e9ac 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -1223,7 +1223,7 @@ BUILTIN_CORE_OPTIONS: 'MutableKeyedOptionDictType' = OrderedDict([
     (OptionKey('strip'),           BuiltinOption(UserBooleanOption, 'Strip targets on install', False)),
     (OptionKey('unity'),           BuiltinOption(UserComboOption, 'Unity build', 'off', choices=['on', 'off', 'subprojects'])),
     (OptionKey('unity_size'),      BuiltinOption(UserIntegerOption, 'Unity block size', (2, None, 4))),
-    (OptionKey('warning_level'),   BuiltinOption(UserComboOption, 'Compiler warning level to use', '1', choices=['0', '1', '2', '3'], yielding=False)),
+    (OptionKey('warning_level'),   BuiltinOption(UserComboOption, 'Compiler warning level to use', '1', choices=['0', '1', '2', '3', 'everything'], yielding=False)),
     (OptionKey('werror'),          BuiltinOption(UserBooleanOption, 'Treat warnings as errors', False, yielding=False)),
     (OptionKey('wrap_mode'),       BuiltinOption(UserComboOption, 'Wrap mode', 'default', choices=['default', 'nofallback', 'nodownload', 'forcefallback', 'nopromote'])),
     (OptionKey('force_fallback_for'), BuiltinOption(UserArrayOption, 'Force fallback for those subprojects', [])),
diff --git a/unittests/allplatformstests.py b/unittests/allplatformstests.py
index 6eced8e..8b78590 100644
--- a/unittests/allplatformstests.py
+++ b/unittests/allplatformstests.py
@@ -2279,6 +2279,9 @@ class AllPlatformTests(BasePlatformTests):
         self.setconf('--warnlevel=3')
         obj = mesonbuild.coredata.load(self.builddir)
         self.assertEqual(obj.options[OptionKey('warning_level')].value, '3')
+        self.setconf('--warnlevel=everything')
+        obj = mesonbuild.coredata.load(self.builddir)
+        self.assertEqual(obj.options[OptionKey('warning_level')].value, 'everything')
         self.wipe()
 
         # But when using -D syntax, it should be 'warning_level'
@@ -2288,6 +2291,9 @@ class AllPlatformTests(BasePlatformTests):
         self.setconf('-Dwarning_level=3')
         obj = mesonbuild.coredata.load(self.builddir)
         self.assertEqual(obj.options[OptionKey('warning_level')].value, '3')
+        self.setconf('-Dwarning_level=everything')
+        obj = mesonbuild.coredata.load(self.builddir)
+        self.assertEqual(obj.options[OptionKey('warning_level')].value, 'everything')
         self.wipe()
 
         # Mixing --option and -Doption is forbidden