build: Use a tuple for pch data

This really isn't a list because it's not homogenous data, it's really
`tuple[str, str | None] | None`, but we're using list length to decide
what to do with it, and that makes for strict null issues, as an
accurate annotation would be `list[str | None]`, which would require a
lot of `is not None` checking. By using a tuple we don't need to keep
checking length, which is more expensive than null checking.

To ensure correctness I annotated some things in the VS backend

1 files changed, 1 insertions, 3 deletions

diff --git a/mesonbuild/backend/xcodebackend.py b/mesonbuild/backend/xcodebackend.py
index 87e1309a6..95a62a02a 100644
--- a/mesonbuild/backend/xcodebackend.py
+++ b/mesonbuild/backend/xcodebackend.py
@@ -1802,9 +1802,7 @@ class XCodeBackend(backends.Backend):
                 # Xcode uses GCC_PREFIX_HEADER which only allows one file per target/executable. Precompiling various header files and
                 # applying a particular pch to each source file will require custom scripts (as a build phase) and build flags per each
                 # file. Since Xcode itself already discourages precompiled headers in favor of modules we don't try much harder here.
-                pchs = target.get_pch('c') + target.get_pch('cpp') + target.get_pch('objc') + target.get_pch('objcpp')
-                # Make sure to use headers (other backends require implementation files like *.c *.cpp, etc; these should not be used here)
-                pchs = [pch for pch in pchs if pch.endswith('.h') or pch.endswith('.hh') or pch.endswith('hpp')]
+                pchs = [t[0] for t in [target.pch['c'], target.pch['cpp']] if t is not None]
                 if pchs:
                     if len(pchs) > 1:
                         mlog.warning(f'Unsupported Xcode configuration: More than 1 precompiled header found "{pchs!s}". Target "{target.name}" might not compile correctly.')