Canonicalize and merge consecutive -Xcompiler flags together.

Makes command-line more readable.

mesonbuild/compilers/cuda.py

@@ -258,6 +258,52 @@ class CudaCompiler(Compiler):
             l = [cls._shield_nvcc_list_arg(s, listmode=False) for s in l]
             return '\,'.join(l)
 
+    @classmethod
+    def _merge_flags(cls, flags: T.List[str]) -> T.List[str]:
+        r"""
+        The flags to NVCC gets exceedingly verbose and unreadable when too many of them
+        are shielded with -Xcompiler. Merge consecutive -Xcompiler-wrapped arguments
+        into one.
+        """
+        if len(flags) <= 1:
+            return flags
+        flagit = iter(flags)
+        xflags = []
+
+        def is_xcompiler_flag_isolated(flag: str) -> bool:
+            return flag == '-Xcompiler'
+        def is_xcompiler_flag_glued(flag: str) -> bool:
+            return flag.startswith('-Xcompiler=')
+        def is_xcompiler_flag(flag: str) -> bool:
+            return is_xcompiler_flag_isolated(flag) or is_xcompiler_flag_glued(flag)
+        def get_xcompiler_val(flag: str, flagit: T.Iterator[str]) -> str:
+            if is_xcompiler_flag_glued(flag):
+                return flag[len('-Xcompiler='):]
+            else:
+                try:
+                    return next(flagit)
+                except StopIteration:
+                    return ""
+
+        ingroup = False
+        for flag in flagit:
+            if not is_xcompiler_flag(flag):
+                ingroup = False
+                xflags.append(flag)
+            elif ingroup:
+                xflags[-1] += ','
+                xflags[-1] += get_xcompiler_val(flag, flagit)
+            elif is_xcompiler_flag_isolated(flag):
+                ingroup = True
+                xflags.append(flag)
+                xflags.append(get_xcompiler_val(flag, flagit))
+            elif is_xcompiler_flag_glued(flag):
+                ingroup = True
+                xflags.append(flag)
+            else:
+                raise ValueError("-Xcompiler flag merging failed, unknown argument form!")
+        return xflags
+
     @classmethod
     def _to_host_flags(cls, flags: T.List[str], phase: _Phase = _Phase.COMPILER) -> T.List[str]:
         """
@@ -431,7 +477,7 @@ class CudaCompiler(Compiler):
                 xflags.append(flag)
                 xflags.append(val)
 
-        return xflags
+        return cls._merge_flags(xflags)
 
     def needs_static_linker(self) -> bool:
         return False