Made it so duplicating a label is an error.

2 files changed, 28 insertions, 3 deletions

diff --git a/doc/casm.html b/doc/casm.html
index 28284f8..31e1d92 100644
--- a/doc/casm.html
+++ b/doc/casm.html
@@ -238,15 +238,18 @@ of a string constant).</li>
 <li>Labels must start in column zero (the left hand most column).</li>
 
   <ul>
+  <li>It is an error to redefine a global label that already exists.</li>
+
   <li>If the label ends with a colon (:) then the colon is removed.</li>
 
   <li>If the label doesn't start with a period (.) then it is assumed a global
   label.</li>
 
   <li>If the label starts with a period (.) then it is assumed to be a local
-  label.  Local labels are associated with the preceding global label.
-  If a global label and related local label have the same name, the local
-  label will be used on expansion.</li>
+  label.  Local labels are associated with the preceding global label.  If
+  a local label has the same name as a global variable the local value will be
+  used on expansion.  If a local label already exists with the same name it
+  is an error.</li>
 
   <li>Any label can be followed by an <code>equ</code> directive, in which case
   the label is set to that value rather than the current program counter.</li>
diff --git a/src/casm.c b/src/casm.c
index bec864b..f4b06e5 100644
--- a/src/casm.c
+++ b/src/casm.c
@@ -892,6 +892,28 @@ static void RunPass(const char *name, FILE *fp, int depth)
                 goto error_handling;
             }
 
+            if (IsFirstPass())
+            {
+                const Label *l;
+
+                if ((l = LabelFind(label, type)))
+                {
+                    if (l->type == GLOBAL_LABEL)
+                    {
+                        snprintf(err, sizeof err, "Global %s already defined",
+                                        label);
+                    }
+                    else
+                    {
+                        snprintf(err, sizeof err, "Local %s already defined",
+                                        label);
+                    }
+
+                    cmdstat = CMD_FAILED;
+                    goto error_handling;
+                }
+            }
+
             /* This may well be updated by a command, but easier to set anyway
             */
             if (options.address24)