Merge pull request cc65#2132 from vrubleg/ulabel

Add support of unnamed labels with @ (.localchar) prefix

doc/ca65.sgml

@@ -829,49 +829,42 @@ names like "Loop". Here is an example:
                 bne    @Loop            ; ERROR: Unknown identifier!
 </verb></tscreen>
 
+
 <sect1>Unnamed labels<p>
 
-If you really want to write messy code, there are also unnamed labels. These
-labels do not have a name (you guessed that already, didn't you?). A colon is
-used to mark the absence of the name.
+If you really want to write messy code, there are also unnamed labels. To define
+an unnamed label, use either <tt>@:</tt> (<tt>.LOCALCHAR</tt> is respected if it
+is set) or sole <tt>:</tt>.
 
-Unnamed labels may be accessed by using the colon plus several minus or plus
-characters as a label designator. Using the '-' characters will create a back
-reference (use the n'th label backwards), using '+' will create a forward
-reference (use the n'th label in forward direction). An example will help to
-understand this:
+To reference an unnamed label, use <tt>@</tt> (<tt>.LOCALCHAR</tt> is respected
+if it is set) or <tt>:</tt> with several <tt>-</tt> or <tt>+</tt> characters.
+The <tt>-</tt> characters will create a back reference (n'th label backwards),
+the <tt>+</tt> will create a forward reference (n'th label in forward direction).
+As an alternative, angle brackets <tt>&lt;</tt> and <tt>&gt;</tt> may be used
+instead of <tt>-</tt> and <tt>+</tt> with the same meaning.
 
-<tscreen><verb>
-        :       lda     (ptr1),y        ; #1
-                cmp     (ptr2),y
-                bne     :+              ; -> #2
-                tax
-                beq     :+++            ; -> #4
-                iny
-                bne     :-              ; -> #1
-                inc     ptr1+1
-                inc     ptr2+1
-                bne     :-              ; -> #1
-
-        :       bcs     :+              ; #2 -> #3
-                ldx     #$FF
-                rts
+Example:
 
-        :       ldx     #$01            ; #3
-        :       rts                     ; #4
+<tscreen><verb>
+        cpy #0
+        beq @++
+    @:
+        sta $2007
+        dey
+        bne @-
+    @:
+        rts
 </verb></tscreen>
 
-As you can see from the example, unnamed labels will make even short
-sections of code hard to understand, because you have to count labels
-to find branch targets (this is the reason why I for my part do
-prefer the "cheap" local labels). Nevertheless, unnamed labels are
-convenient in some situations, so it's your decision.
+Unnamed labels may make even short sections of code hard to understand, because
+you have to count labels to find branch targets. It's better to prefer the
+"cheap" local labels. Nevertheless, unnamed labels are convenient in some
+situations, so it's up to your discretion.
 
 <em/Note:/ <ref id="scopes" name="Scopes"> organize named symbols, not
 unnamed ones, so scopes don't have an effect on unnamed labels.
 
 
-
 <sect1>Using macros to define labels and constants<p>
 
 While there are drawbacks with this approach, it may be handy in a few rare

src/ca65/main.c

@@ -707,6 +707,24 @@ static void OneLine (void)
         NextTok ();
     }
 
+    /* Handle @-style unnamed labels */
+    if (CurTok.Tok == TOK_ULABEL) {
+        if (CurTok.IVal != 0) {
+            Error ("Invalid unnamed label definition");
+        }
+        ULabDef ();
+        NextTok ();
+
+        /* Skip the colon. If NoColonLabels is enabled, allow labels without
+        ** a colon if there is no whitespace before the identifier.
+        */
+        if (CurTok.Tok == TOK_COLON) {
+            NextTok ();
+        } else if (CurTok.WS || !NoColonLabels) {
+            Error ("':' expected");
+        }
+    }
+
     /* If the first token on the line is an identifier, check for a macro or
     ** an instruction.
     */

src/ca65/scanner.c

@@ -1124,17 +1124,33 @@ void NextRawTok (void)
     /* Local symbol? */
     if (C == LocalStart) {
 
-        /* Read the identifier. */
-        ReadIdent ();
+        NextChar ();
+
+        if (IsIdChar (C)) {
+            /* Read a local identifier */
+            CurTok.Tok = TOK_LOCAL_IDENT;
+            SB_AppendChar (&CurTok.SVal, LocalStart);
+            ReadIdent ();
+        } else {
+            /* Read an unnamed label */
+            CurTok.IVal = 0;
+            CurTok.Tok = TOK_ULABEL;
 
-        /* Start character alone is not enough */
-        if (SB_GetLen (&CurTok.SVal) == 1) {
-            Error ("Invalid cheap local symbol");
-            goto Again;
+            if (C == '-' || C == '<') {
+                int PrevC = C;
+                do {
+                    --CurTok.IVal;
+                    NextChar ();
+                } while (C == PrevC);
+            } else if (C == '+' || C == '>') {
+                int PrevC = C;
+                do {
+                    ++CurTok.IVal;
+                    NextChar ();
+                } while (C == PrevC);
+            }
         }
 
-        /* A local identifier */
-        CurTok.Tok = TOK_LOCAL_IDENT;
         return;
     }
 
@@ -1314,22 +1330,30 @@ void NextRawTok (void)
                     break;
 
                 case '-':
+                case '<':
+                {
+                    int PrevC = C;
                     CurTok.IVal = 0;
                     do {
                         --CurTok.IVal;
                         NextChar ();
-                    } while (C == '-');
+                    } while (C == PrevC);
                     CurTok.Tok = TOK_ULABEL;
                     break;
+                }
 
                 case '+':
+                case '>':
+                {
+                    int PrevC = C;
                     CurTok.IVal = 0;
                     do {
                         ++CurTok.IVal;
                         NextChar ();
-                    } while (C == '+');
+                    } while (C == PrevC);
                     CurTok.Tok = TOK_ULABEL;
                     break;
+                }
 
                 case '=':
                     NextChar ();

src/ca65/token.h

@@ -71,7 +71,7 @@ typedef enum token_t {
     TOK_REG,            /* Sweet16 R.. register (in sweet16 mode) */
 
     TOK_ASSIGN,         /* := */
-    TOK_ULABEL,         /* :++ or :-- */
+    TOK_ULABEL,         /* An unnamed label */
 
     TOK_EQ,             /* = */
     TOK_NE,             /* <> */

src/ca65/ulabel.c

@@ -107,8 +107,12 @@ ExprNode* ULabRef (int Which)
     int     Index;
     ULabel* L;
 
-    /* Which can never be 0 */
-    PRECONDITION (Which != 0);
+    /* Which should not be 0 */
+    if (Which == 0) {
+        Error ("Invalid unnamed label reference");
+        /* We must return something valid */
+        return GenCurrentPC();
+    }
 
     /* Get the index of the referenced label */
     if (Which > 0) {

test/asm/listing/060-ulabel.s

@@ -0,0 +1,25 @@
+; Test new-style (@:) and legacy-style (:) unnamed labels.
+; Make sure that they have identical behavior.
+
+.ORG $0000
+
+@:  nop
+:   nop
+.ASSERT @<< = $0000, error
+.ASSERT @-- = $0000, error
+.ASSERT :<< = $0000, error
+.ASSERT :-- = $0000, error
+.ASSERT @< = $0001, error
+.ASSERT @- = $0001, error
+.ASSERT :< = $0001, error
+.ASSERT :- = $0001, error
+.ASSERT @> = $0002, error
+.ASSERT @+ = $0002, error
+.ASSERT :> = $0002, error
+.ASSERT :+ = $0002, error
+.ASSERT @>> = $0003, error
+.ASSERT @++ = $0003, error
+.ASSERT :>> = $0003, error
+.ASSERT :++ = $0003, error
+@:  nop
+:   nop