Consistently handle negative shifted macro args (#2014)

Negative macro arguments count from the end, i.e. `\<-1>`
is equivalent to `\<_NARG>`, even after `shift`ing them.

Negative arguments cannot be used to access shifted values.

include/asm/macro.hpp

@@ -13,7 +13,7 @@ struct MacroArgs {
 	std::vector<std::shared_ptr<std::string>> args;
 
 	uint32_t nbArgs() const { return args.size() - shift; }
-	std::shared_ptr<std::string> getArg(int32_t i) const;
+	std::shared_ptr<std::string> getArg(int32_t num) const;
 	std::shared_ptr<std::string> getAllArgs() const;
 
 	void appendArg(std::shared_ptr<std::string> arg);

src/asm/macro.cpp

@@ -8,18 +8,26 @@
 #include <string.h>
 #include <string>
 
+#include "helpers.hpp" // assume
+
 #include "asm/warning.hpp"
 
-std::shared_ptr<std::string> MacroArgs::getArg(int32_t i) const {
-	// Bracketed macro arguments adjust negative indexes such that -1 is the last argument.
-	if (i < 0) {
-		i += args.size() + 1;
+std::shared_ptr<std::string> MacroArgs::getArg(int32_t num) const {
+	assume(num != 0);
+	if (num > 0) {
+		// Macro arguments adjust 1-based indexes by the shift amount.
+		if (size_t i = num - 1 + shift; i < args.size()) {
+			return args[i];
+		}
+	} else {
+		// Bracketed macro arguments adjust negative indexes such that -1 is the last argument.
+		if (num == INT32_MIN || static_cast<size_t>(-num) > args.size()) {
+			return nullptr;
+		} else if (size_t i = args.size() - static_cast<size_t>(-num); i >= shift) {
+			return args[i];
+		}
 	}
-
-	int32_t realIndex = i + shift - 1;
-
-	return realIndex < 0 || static_cast<uint32_t>(realIndex) >= args.size() ? nullptr
-	                                                                        : args[realIndex];
+	return nullptr;
 }
 
 std::shared_ptr<std::string> MacroArgs::getAllArgs() const {

test/asm/negative-shifted-macro-args.asm

@@ -0,0 +1,22 @@
+MACRO test
+	static_assert _NARG == 10
+	println _NARG
+	println \1, \<10>, \<-1>, \<-10>
+	println \<999>
+	println \<-999>
+	shift 3
+	println _NARG
+	println \1, \7, \<-1>, \<-7>
+	println \<8>
+	println \<-8>
+	println \<-999>
+	shift 7
+	println _NARG
+	println \1
+	println \<-1>
+	shift -10
+	println _NARG
+	println \<-2_147_483_648>
+ENDM
+
+test "a", "b", "c", "d", "e", "f", "g", "h", "i", "j"

test/asm/negative-shifted-macro-args.err

@@ -0,0 +1,19 @@
+error: Macro argument `\<999>` not defined
+    at negative-shifted-macro-args.asm::test(5) <- negative-shifted-macro-args.asm(22)
+error: Macro argument `\<-999>` not defined
+    at negative-shifted-macro-args.asm::test(6) <- negative-shifted-macro-args.asm(22)
+error: Macro argument `\<8>` not defined
+    at negative-shifted-macro-args.asm::test(10) <- negative-shifted-macro-args.asm(22)
+error: Macro argument `\<-8>` not defined
+    at negative-shifted-macro-args.asm::test(11) <- negative-shifted-macro-args.asm(22)
+error: Macro argument `\<-999>` not defined
+    at negative-shifted-macro-args.asm::test(12) <- negative-shifted-macro-args.asm(22)
+error: Macro argument `\1` not defined
+    at negative-shifted-macro-args.asm::test(15) <- negative-shifted-macro-args.asm(22)
+error: Macro argument `\<-1>` not defined
+    at negative-shifted-macro-args.asm::test(16) <- negative-shifted-macro-args.asm(22)
+error: Number in bracketed macro argument is too large
+    at negative-shifted-macro-args.asm::test(19) <- negative-shifted-macro-args.asm(22)
+error: syntax error, unexpected >
+    at negative-shifted-macro-args.asm::test(19) <- negative-shifted-macro-args.asm(22)
+Assembly aborted with 9 errors

test/asm/negative-shifted-macro-args.out

@@ -0,0 +1,13 @@
+$A
+ajja
+
+
+$7
+djjd
+
+
+
+$0
+
+
+$A