Deprecate LDH with $00-$FF (#1575)

src/asm/parser.y

@@ -1949,13 +1949,23 @@ z80_ldd:
 
 z80_ldh:
 	Z80_LDH MODE_A COMMA op_mem_ind {
-		$4.makeCheckHRAM();
+		if ($4.makeCheckHRAM()) {
+			warning(
+			    WARNING_OBSOLETE,
+			    "LDH is deprecated with values from $00 to $FF; use $FF00 to $FFFF\n"
+			);
+		}
 
 		sect_ConstByte(0xF0);
 		sect_RelByte($4, 1);
 	}
 	| Z80_LDH op_mem_ind COMMA MODE_A {
-		$2.makeCheckHRAM();
+		if ($2.makeCheckHRAM()) {
+			warning(
+			    WARNING_OBSOLETE,
+			    "LDH is deprecated with values from $00 to $FF; use $FF00 to $FFFF\n"
+			);
+		}
 
 		sect_ConstByte(0xE0);
 		sect_RelByte($2, 1);

src/asm/rpn.cpp

@@ -568,16 +568,20 @@ void Expression::makeBinaryOp(RPNCommand op, Expression &&src1, Expression const
 	}
 }
 
-void Expression::makeCheckHRAM() {
+bool Expression::makeCheckHRAM() {
 	isSymbol = false;
 	if (!isKnown()) {
 		*reserveSpace(1) = RPN_HRAM;
 	} else if (int32_t val = value(); val >= 0xFF00 && val <= 0xFFFF) {
 		// That range is valid, but only keep the lower byte
 		data = val & 0xFF;
-	} else if (val < 0 || val > 0xFF) {
+	} else if (val >= 0 && val <= 0xFF) {
+		// That range is valid, but deprecated
+		return true;
+	} else {
 		error("Source address $%" PRIx32 " not between $FF00 to $FFFF\n", val);
 	}
+	return false;
 }
 
 void Expression::makeCheckRST() {

src/link/patch.cpp

@@ -356,6 +356,12 @@ static int32_t computeRPNExpr(Patch const &patch, std::vector<Symbol> const &fil
 					isError = true;
 				}
 				value = 0;
+			} else if (value >= 0 && value <= 0xFF) {
+				warning(
+				    patch.src,
+				    patch.lineNo,
+				    "LDH is deprecated with values from $00 to $FF; use $FF00 to $FFFF"
+				);
 			}
 			value &= 0xFF;
 			break;