C++: Remove decimal types from the dbscheme

cpp/downgrades/d2d611b3fdcc7c4fe370f0d115200a3aa6ad5837/upgrade.properties

@@ -0,0 +1,2 @@
+description: Remove _Decimal{32,64,128} types
+compatibility: full

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -617,9 +617,9 @@ case @builtintype.kind of
 | 37 = @signed_int128         // signed __int128
 | 38 = @float128              // __float128
 | 39 = @complex_float128      // _Complex __float128
-| 40 = @decimal32             // _Decimal32
-| 41 = @decimal64             // _Decimal64
-| 42 = @decimal128            // _Decimal128
+// ... 40 _Decimal32
+// ... 41 _Decimal64
+// ... 42 _Decimal128
 | 43 = @char16_t
 | 44 = @char32_t
 | 45 = @std_float32           // _Float32

cpp/ql/lib/upgrades/a42ce5fc943254097f85471b94ae2247e819104a/builtintypes.ql

@@ -0,0 +1,11 @@
+class BuiltinType extends @builtintype {
+  string toString() { none() }
+}
+
+predicate isDecimalBuiltinType(BuiltinType type) { builtintypes(type, _, [40, 41, 42], _, _, _) }
+
+from BuiltinType type, string name, int kind, int kind_new, int size, int sign, int alignment
+where
+  builtintypes(type, name, kind, size, sign, alignment) and
+  if isDecimalBuiltinType(type) then kind_new = 1 else kind_new = kind
+select type, name, kind_new, size, sign, alignment

cpp/ql/lib/upgrades/a42ce5fc943254097f85471b94ae2247e819104a/upgrade.properties

@@ -0,0 +1,3 @@
+description: Remove _Decimal{32,64,128} types
+compatibility: partial
+builtintypes.rel: run builtintypes.qlo