Error parsing blackbox: Clash.Sized.Vector.head

[bgamari]

The following program fails to compile to Verilog with clash master (although I suspect that this isn't a new issue):

{-# LANGUAGE DataKinds #-}

module Repro where

import Clash.Prelude
import Prelude ()

topEntity
    :: Signal System (Vec 4 (Vec 4 (Unsigned 32)))
    -> Signal System (Vec 4 (Unsigned 32))
topEntity = f

f
    :: Signal System (Vec n (Vec 4 (Unsigned 32)))
    -> Signal System (Vec n (Unsigned 32))
f x = fmap (fmap head) x
{-# OPAQUE f #-}

{-# ANN topEntity
  (Synthesize
    { t_name   = "repro"
    , t_inputs = [ PortName "inp" ]
    , t_output = PortName "outp"
    }) #-}

Concretely, the failure is (although this error includes a fair amount of additional context that I have added in https://github.com/bgamari/clash-compiler/tree/wip/blackbox-parse-failure):

<no location info>: error:                  
    Clash error call:                  
    error while parsing blackbox: Clash.Sized.Vector.head                               
    in component Hi_topEntity_f                                                         
    error:
    :1:38: error: expected: "[\\", "\\]", "]", "~ACTIVEEDGE", "~AND", "~ARG",
        "~ARGN", "~CMPLE", "~COMPNAME", "~CONST", "~CTXNAME", "~DEPTH", "~DEVNULL",
        "~ENDGENERATE", "~ERROR", "~ERRORO", "~FILE", "~FROMBV", "~GENERATE",
        "~GENSYM", "~INCLUDENAME", "~INDEXTYPE", "~ISACTIVEENABLE", "~ISACTIVEHIGH",
        "~ISINITDEFINED", "~ISLIT", "~ISSCALAR", "~ISSYNC", "~ISUNDEFINED",
        "~ISVAR", "~IW64", "~LENGTH", "~LIT", "~LONGESTPERIOD", "~MAXINDEX",
        "~NAME", "~OTHERSYN", "~OUTPUTUSAGE", "~OUTPUTWIREREG", "~PERIOD",
        "~REPEAT", "~RESULT", "~SEL", "~SIGD", "~SIGDO", "~SIZE", "~STRCMP", "~SYM",
        "~TAG", "~TEMPLATE", "~TOBV", "~TYP", "~TYPEL", "~TYPM", "~TYPMO", "~TYPO",
        "~VAR", "~VARS", "~VIVADO"
    1 | assign ~RESULT = ~FROMBV[~VAR[vec][0][~SIZE[~TYP[0]]-1 -: ~SIZE[~TYPO]]][~>
      |                                      ^                                     
    template:
    assign ~RESULT = ~FROMBV[~VAR[vec][0][~SIZE[~TYP[0]]-1 -: ~SIZE[~TYPO]]][~TYPO];
    
    
    
    CallStack (from HasCallStack):
      error, called at src/Clash/Netlist/BlackBox/Util.hs:687:5 in clash-lib-1.9.0-inplace:Clash.Netlist.BlackBox.Util

Specifically, the problem is the template, which differs from that defined in clash-lib/prims/verilog/Clash_Sized_Vector.primitives.yaml:

+    assign ~RESULT = ~FROMBV[~VAR[vec][0][~SIZE[~TYP[0]]-1 -: ~SIZE[~TYPO]]][~TYPO];
-    assign ~RESULT = ~FROMBV[~VAR[vec][0][\\~SIZE[~TYP[0]]-1 -: ~SIZE[~TYPO]\\]][~TYPO];

[bgamari]

As noted above, the problem here appears to be that something rewrote [\\ (respectively \\]) to [ (resp. ]) in the template string. The cause of this appears to be Clash.Netlist.BlackBox.mkFunInput, which does some rather dodgy things to construct a black-box from another black-box. Specifically, it uses prettyBlackBox to render a blackbox to a string, which it then treats as an identifier. This fails as prettyBlackBox fails to escape [ and ] correctly.

[DigitalBrains1]

I think it's the same as #2809 . I had a lot of trouble finding the commit that dealt with this issue, but I was sure I had seen a commit deal with it. Finally thought to search issues instead, and it turns out we never committed the fix that Leon wrote (or started on? Since it never seems to have made the PR stage?). But you can still peek at the code in the fix-map-head tree. I don't know what the state is of the fix.

[bgamari]

Thanks, @DigitalBrains1. I'll have a look, take what I can from the fix and update my MR.

[bgamari]

This should be resolved by #2989.