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Prevent defining invalid local labels

Fixes #913

--- a/src/asm/symbol.c

+++ b/src/asm/symbol.c

@@ -245,18 +245,18 @@

 struct Symbol *sym_FindScopedSymbol(char const *symName)

 {

-	char const *dotPtr = strchr(symName, '.');

+	char const *localName = strchr(symName, '.');

-	if (dotPtr) {

-		if (strchr(dotPtr + 1, '.'))

+	if (localName) {

+		if (strchr(localName + 1, '.'))

 			fatalerror("'%s' is a nonsensical reference to a nested local symbol\n",

 				   symName);

 		/* If auto-scoped local label, expand the name */

-		if (dotPtr == symName) { /* Meaning, the name begins with the dot */

-			char fullname[MAXSYMLEN + 1];

+		if (localName == symName) { /* Meaning, the name begins with the dot */

+			char fullName[MAXSYMLEN + 1];

-			fullSymbolName(fullname, sizeof(fullname), symName, labelScope);

-			return sym_FindExactSymbol(fullname);

+			fullSymbolName(fullName, sizeof(fullName), symName, labelScope);

+			return sym_FindExactSymbol(fullName);

 		}

 	}

 	return sym_FindExactSymbol(symName);

@@ -533,7 +533,7 @@

 }

 /*

- * Add a local (.name or Parent.name) relocatable symbol

+ * Add a local (`.name` or `Parent.name`) relocatable symbol

  */

 struct Symbol *sym_AddLocalLabel(char const *symName)

 {

@@ -541,34 +541,40 @@

 		error("Local label '%s' in main scope\n", symName);

 		return NULL;

 	}

+	assert(!strchr(labelScope, '.')); /* Assuming no dots in `labelScope` */

-	char fullname[MAXSYMLEN + 1];

+	char fullName[MAXSYMLEN + 1];

+	char const *localName = strchr(symName, '.');

-	if (symName[0] == '.') {

-		/* If symbol is of the form `.name`, expand to the full `Parent.name` name */

-		fullSymbolName(fullname, sizeof(fullname), symName, labelScope);

-		symName = fullname; /* Use the expanded name instead */

+	assert(localName); /* There should be at least one dot in `symName` */

+	/* Check for something after the dot in `localName` */

+	if (localName[1] == '\0') {

+		fatalerror("'%s' is a nonsensical reference to an empty local label\n",

+			   symName);

+	}

+	/* Check for more than one dot in `localName` */

+	if (strchr(localName + 1, '.'))

+		fatalerror("'%s' is a nonsensical reference to a nested local label\n",

+			   symName);

+

+	if (localName == symName) {

+		/* Expand `symName` to the full `labelScope.symName` name */

+		fullSymbolName(fullName, sizeof(fullName), symName, labelScope);

+		symName = fullName;

 	} else {

 		size_t i = 0;

-		/* Otherwise, check that `Parent` is in fact the current scope */

+		/* Find where `labelScope` and `symName` first differ */

 		while (labelScope[i] && symName[i] == labelScope[i])

 			i++;

-		/* Assuming no dots in `labelScope` */

-		assert(strchr(&symName[i], '.')); /* There should be at least one dot, though */

-		size_t parentLen = i + (strchr(&symName[i], '.') - symName);

-		/*

-		 * Check that `labelScope[i]` ended the check, guaranteeing that `symName` is at

-		 * least as long, and then that this was the entire `Parent` part of `symName`.

-		 */

+		/* Check that `symName` starts with `labelScope` and then a '.' */

 		if (labelScope[i] != '\0' || symName[i] != '.') {

+			size_t parentLen = localName - symName;

+

 			assert(parentLen <= INT_MAX);

 			error("Not currently in the scope of '%.*s'\n", (int)parentLen, symName);

 		}

-		if (strchr(&symName[parentLen + 1], '.')) /* There will at least be a terminator */

-			fatalerror("'%s' is a nonsensical reference to a nested local label\n",

-				   symName);

 	}

 	return addLabel(symName);

--- a/test/asm/empty-local.err

+++ b/test/asm/empty-local.err

@@ -1,0 +1,2 @@

+FATAL: empty-local.asm(5):

+    'Label.' is a nonsensical reference to an empty local label

--- /dev/null

+++ b/test/asm/multiple-dots-local.asm

@@ -1,0 +1,7 @@

+SECTION "sec", ROM0

+

+Parent:

+Parent.heir:

+	db 0

+Parent...spare:

+	db 1

--- /dev/null

+++ b/test/asm/multiple-dots-local.err

@@ -1,0 +1,2 @@

+FATAL: multiple-dots-local.asm(6):

+    'Parent...spare' is a nonsensical reference to a nested local label

--- /dev/null

+++ b/test/asm/nested-local-reference.asm

@@ -1,0 +1,8 @@

+SECTION "sec", ROM0

+

+Parent:

+Parent.child:

+	db 0

+.grandchild:

+	db 1

+	dw Parent.child.grandchild

--- /dev/null

+++ b/test/asm/nested-local-reference.err

@@ -1,0 +1,2 @@

+FATAL: nested-local-reference.asm(8):

+    'Parent.child.grandchild' is a nonsensical reference to a nested local symbol

--- /dev/null

+++ b/test/asm/nested-local.asm

@@ -1,0 +1,7 @@

+SECTION "sec", ROM0

+

+Parent:

+Parent.child:

+	db 0

+Parent.child.grandchild:

+	db 1

--- /dev/null

+++ b/test/asm/nested-local.err

@@ -1,0 +1,2 @@

+FATAL: nested-local.asm(6):

+    'Parent.child.grandchild' is a nonsensical reference to a nested local label

--- a/test/asm/remote-local-noexist.asm

+++ b/test/asm/remote-local-noexist.asm

@@ -4,4 +4,4 @@

 .child:

 	db 0

 NotParent:

-	dw Parent.child.fail

+	dw Parent.orphan

--- a/test/asm/remote-local-noexist.err

+++ b/test/asm/remote-local-noexist.err

@@ -1,2 +1,0 @@

-FATAL: remote-local-noexist.asm(7):

-    'Parent.child.fail' is a nonsensical reference to a nested local symbol

--- a/test/asm/sym-scope.err

+++ b/test/asm/sym-scope.err

@@ -3,7 +3,7 @@

 ERROR: sym-scope.asm(5):

     Local label 'Nice.try' in main scope

 ERROR: sym-scope.asm(17):

-    Not currently in the scope of 'Parentheses.check'

+    Not currently in the scope of 'Parentheses'

 ERROR: sym-scope.asm(21):

-    Not currently in the scope of 'Parent.check'

+    Not currently in the scope of 'Parent'

 error: Assembly aborted (4 errors)!