Removed the limit on the number of traces in dumpVCD (#3083)

`dumpVCD` was limited to 93 traces, because it could only generate
single character trace identifier codes. The codes are now generated ad
infinitum, and the restriction has been removed.

Additionally, single bit traces were logged with an extra newline,
causing empty lines in the VCD. This has been removed as well.

Fixes: #3082

Author: marijn-qbaylogic

changelog/2025-11-17T21_35_22+01_00_fixed_dumpvcd_trace_limit

@@ -0,0 +1 @@
+FIXED: Removed the limit on the number of traces in `dumpVCD`. Also removed unnecessary double newlines after 1-bit signals. [#3082](https://github.com/clash-lang/clash-compiler/issues/3082)

clash-prelude/src/Clash/Signal/Trace.hs

@@ -115,6 +115,7 @@ import           Data.IORef
 import           Data.List             (foldl')
 #endif
 import           Data.List             (foldl1', unzip4, transpose, uncons)
+import           Data.List.Extra       (snoc)
 import qualified Data.Map.Strict       as Map
 import           Data.Maybe            (fromMaybe, catMaybes)
 import qualified Data.Text             as Text
@@ -342,8 +343,6 @@ dumpVCD## (offset, cycles) traceMap now
       error $ "dumpVCD: cycles was " ++ show cycles ++ ", but cannot be negative."
   | null traceMap =
       error $ "dumpVCD: no traces found. Extend the given trace names."
-  | Map.size traceMap > 126 - 33 =
-      Left $ "Tracemap contains more than 93 traces, which is not supported by VCD."
   | (nm:_) <- offensiveNames =
       Left $ unwords [ "Trace '" ++ nm ++ "' contains"
                      , "non-printable ASCII characters, which is not"
@@ -366,7 +365,10 @@ dumpVCD## (offset, cycles) traceMap now
  where
   offensiveNames = filter (any (not . printable)) traceNames
 
-  labels = map chr [33..126]
+  -- Generate labels in the pattern a,b,c,aa,ab,ac,ba,bb,bc,ca,cb,cc,aaa,...
+  labels = concatMap (\s -> map (snoc s) alphabet) ([]: labels)
+   where
+    alphabet = map chr [33..126]
 
   timescale = foldl1' gcd (Map.keys periodMap)
   periodMap = toPeriodMap traceMap
@@ -407,22 +409,22 @@ dumpVCD## (offset, cycles) traceMap now
   headerTimescale  = ["$timescale", (show timescale) ++ "ps", "$end"]
   headerWires      = [ Text.unwords $ headerWire w l n
                      | (w, l, n) <- (zip3 widths labels traceNames)]
-  headerWire w l n = map Text.pack ["$var wire", show w, [l], n, "$end"]
+  headerWire w l n = map Text.pack ["$var wire", show w, l, n, "$end"]
   initValues       = map Text.pack $ zipWith ($) formatters inits
 
   formatters = zipWith format widths labels
   inits = map (maybe (error "dumpVCD##: empty value") fst . uncons) valuess'
   tails = map changed valuess'
 
   -- | Format single value according to VCD spec
-  format :: Width -> Char -> Value -> String
-  format 1 label (0,0)   = ['0', label, '\n']
-  format 1 label (0,1)   = ['1', label, '\n']
-  format 1 label (1,_)   = ['x', label, '\n']
+  format :: Width -> String -> Value -> String
+  format 1 label (0,0)   = '0': label
+  format 1 label (0,1)   = '1': label
+  format 1 label (1,_)   = 'x': label
   format 1 label (mask,val) =
     error $ "Can't format 1 bit wide value for " ++ show label ++ ": value " ++ show val ++ " and mask " ++ show mask
   format n label (mask,val) =
-    "b" ++ map digit (reverse [0..n-1]) ++ " " ++ [label]
+    "b" ++ map digit (reverse [0..n-1]) ++ " " ++ label
     where
       digit d = case (testBit mask d, testBit val d) of
         (False,False) -> '0'