Add -Wsingle-union warning for UNION without NEXTU (#2170)

contrib/bash_compl/_rgbasm.bash

@@ -193,6 +193,7 @@ _rgbasm_completions() {
 				purge
 				shift
 				shift-amount
+				single-union
 				truncation
 				unmapped-char
 				unmatched-directive

contrib/zsh_compl/_rgbasm

@@ -25,6 +25,7 @@ _rgbasm_warnings() {
 		'purge:Warn when purging exported symbols or labels'
 		'shift:Warn when shifting negative values'
 		'shift-amount:Warn when a shift'\''s operand is negative or \> 32'
+		'single-union:Warn on UNION without NEXTU'
 		'truncation:Warn when implicit truncation loses bits'
 		'unmapped-char:Warn on unmapped character'
 		'unmatched-directive:Warn on unmatched directive pair'

include/asm/warning.hpp

@@ -30,6 +30,7 @@ enum WarningID {
 	WARNING_OBSOLETE,             // Obsolete/deprecated things
 	WARNING_SHIFT,                // Undefined `SHIFT` behavior
 	WARNING_SHIFT_AMOUNT,         // Strange `SHIFT` amount
+	WARNING_SINGLE_UNION,         // `UNION` without `NEXTU`
 	WARNING_UNMATCHED_DIRECTIVE,  // `PUSH[C|O|S]` without `POP[C|O|S]`
 	WARNING_UNTERMINATED_LOAD,    // `LOAD` without `ENDL`
 	WARNING_USER,                 // User-defined `WARN`ings

man/rgbasm.1

@@ -517,6 +517,12 @@ Warn when shifting right a negative value.
 Use a division by 2**N instead.
 .It Fl Wshift-amount
 Warn when a shift's operand is negative or greater than 32.
+.It Fl Wsingle-union
+Warn when a
+.Ic UNION
+construct has no
+.Ic NEXTU
+alternatives.
 .It Fl Wtruncation=
 Warn when an implicit truncation (for example,
 .Ic db

src/asm/section.cpp

@@ -38,6 +38,7 @@ using namespace std::literals;
 struct UnionStackEntry {
 	uint32_t start;
 	uint32_t size;
+	bool hasNextu;
 };
 
 struct SectionStackEntry {
@@ -782,7 +783,7 @@ void sect_StartUnion() {
 		return;
 	}
 
-	currentUnionStack.push({.start = curOffset, .size = 0});
+	currentUnionStack.push({.start = curOffset, .size = 0, .hasNextu = false});
 }
 
 static void endUnionMember() {
@@ -801,6 +802,7 @@ void sect_NextUnionMember() {
 		return;
 	}
 	endUnionMember();
+	currentUnionStack.top().hasNextu = true;
 }
 
 void sect_EndUnion() {
@@ -808,6 +810,9 @@ void sect_EndUnion() {
 		error("Found `ENDU` outside of a `UNION` construct");
 		return;
 	}
+	if (!currentUnionStack.top().hasNextu) {
+		warning(WARNING_SINGLE_UNION, "`UNION` construct has no `NEXTU` alternatives");
+	}
 	endUnionMember();
 	curOffset += currentUnionStack.top().size;
 	currentUnionStack.pop();

src/asm/warning.cpp

@@ -37,6 +37,7 @@ Diagnostics<WarningLevel, WarningID> warnings = {
         {"obsolete",             LEVEL_DEFAULT   },
         {"shift",                LEVEL_EVERYTHING},
         {"shift-amount",         LEVEL_EVERYTHING},
+        {"single-union",         LEVEL_EVERYTHING},
         {"unmatched-directive",  LEVEL_EXTRA     },
         {"unterminated-load",    LEVEL_EXTRA     },
         {"user",                 LEVEL_DEFAULT   },

test/asm/continues-after-missing-include/a.asm

@@ -5,6 +5,7 @@ SECTION "test", WRAM0
 UNION
 INCLUDE "nonexistent1.inc"
 WARN "still going!"
+NEXTU
 INCLUDE "nonexistent2.inc"
 WARN "and going!"
 ENDU

test/asm/continues-after-missing-include/a.err

@@ -1,4 +1,4 @@
 warning: still going! [-Wuser]
     at continues-after-missing-include/a.asm(7)
 warning: and going! [-Wuser]
-    at continues-after-missing-include/a.asm(9)
+    at continues-after-missing-include/a.asm(10)

test/asm/continues-after-missing-preinclude/a.asm

@@ -5,6 +5,7 @@ SECTION "test", WRAM0
 UNION
 INCLUDE "nonexistent1.inc"
 WARN "still going!"
+NEXTU
 INCLUDE "nonexistent2.inc"
 WARN "and going!"
 ENDU

test/asm/continues-after-missing-preinclude/a.err

@@ -1,4 +1,4 @@
 warning: still going! [-Wuser]
     at continues-after-missing-preinclude/a.asm(7)
 warning: and going! [-Wuser]
-    at continues-after-missing-preinclude/a.asm(9)
+    at continues-after-missing-preinclude/a.asm(10)

test/asm/single-union.err

@@ -0,0 +1,2 @@
+warning: `UNION` construct has no `NEXTU` alternatives [-Wsingle-union]
+    at single-union.asm(4)