compilers: Add optimization=plain option

https://github.com/mesonbuild/meson/pull/9287 changed the `optimization=0`
to pass `-O0` to the compiler. This change is reasonable by itself
but unfortunately, it breaks `buildtype=plain`, which promises
that “no extra build flags are used”.

`buildtype=plain` is important for distros like NixOS,
which manage compiler flags for optimization and hardening
themselves.

Let’s introduce a new optimization level that does nothing
and set it as the default for `buildtype=plain`.

1 files changed, 4 insertions, 2 deletions

diff --git a/mesonbuild/compilers/d.py b/mesonbuild/compilers/d.py
index 54f0d9a..fbdf288 100644
--- a/mesonbuild/compilers/d.py
+++ b/mesonbuild/compilers/d.py
@@ -66,7 +66,8 @@ d_feature_args = {'gcc':  {'unittest': '-funittest',
                            }
                   }  # type: T.Dict[str, T.Dict[str, str]]
 
-ldc_optimization_args = {'0': [],
+ldc_optimization_args = {'plain': [],
+                         '0': [],
                          'g': [],
                          '1': ['-O1'],
                          '2': ['-O2'],
@@ -74,7 +75,8 @@ ldc_optimization_args = {'0': [],
                          's': ['-Oz'],
                          }  # type: T.Dict[str, T.List[str]]
 
-dmd_optimization_args = {'0': [],
+dmd_optimization_args = {'plain': [],
+                         '0': [],
                          'g': [],
                          '1': ['-O'],
                          '2': ['-O'],