core: Make variable shadowing a compile-time error

Now that we have most of core free of shadowing, we can enable the
warning as an error to catch anything that may be remaining and also
eliminate this class of logic bug entirely.

src/core/CMakeLists.txt

@@ -651,20 +651,17 @@ endif()
 
 if (MSVC)
     target_compile_options(core PRIVATE
-        # 'expression' : signed/unsigned mismatch
-        /we4018
-        # 'argument' : conversion from 'type1' to 'type2', possible loss of data (floating-point)
-        /we4244
-        # 'conversion' : conversion from 'type1' to 'type2', signed/unsigned mismatch
-        /we4245
-        # 'operator': conversion from 'type1:field_bits' to 'type2:field_bits', possible loss of data
-        /we4254
-        # 'var' : conversion from 'size_t' to 'type', possible loss of data
-        /we4267
-        # 'context' : truncation from 'type1' to 'type2'
-        /we4305
-        # 'function' : not all control paths return a value
-        /we4715
+        /we4018 # 'expression' : signed/unsigned mismatch
+        /we4244 # 'argument' : conversion from 'type1' to 'type2', possible loss of data (floating-point)
+        /we4245 # 'conversion' : conversion from 'type1' to 'type2', signed/unsigned mismatch
+        /we4254 # 'operator': conversion from 'type1:field_bits' to 'type2:field_bits', possible loss of data
+        /we4267 # 'var' : conversion from 'size_t' to 'type', possible loss of data
+        /we4305 # 'context' : truncation from 'type1' to 'type2'
+        /we4456 # Declaration of 'identifier' hides previous local declaration
+        /we4457 # Declaration of 'identifier' hides function parameter
+        /we4458 # Declaration of 'identifier' hides class member
+        /we4459 # Declaration of 'identifier' hides global declaration
+        /we4715 # 'function' : not all control paths return a value
     )
 else()
     target_compile_options(core PRIVATE
@@ -672,6 +669,7 @@ else()
         -Werror=ignored-qualifiers
         -Werror=implicit-fallthrough
         -Werror=sign-compare
+        -Werror=shadow
 
         $<$<CXX_COMPILER_ID:GNU>:-Werror=class-memaccess>
         $<$<CXX_COMPILER_ID:GNU>:-Werror=unused-but-set-parameter>