Net names are not escaped properly for vivado tcl

[rroohhh]

It seems like net names are not properly escaped for vivado tcl scripts, atleast $ is causing problems.

This example:

from nmigen import *
from nmigen_boards.zturn_lite_z010 import *

class Test(Elaboratable):
    def elaborate(self, plat):
        m = Module()

        dummy1 = Signal()

        clk = Signal(name="clk$1")
        m.d.comb += dummy1.eq(clk)
        plat.add_clock_constraint(clk, 100_000_000)

        return m


plat = ZTurnLiteZ010Platform()

t = Test()

plat.build(t)

causes vivado to emit the following message:

Parsing XDC File [/data/projects/nmigen_bugs/build/top.xdc]
CRITICAL WARNING: [Common 17-1548] Command failed: can't read "1": no such variable
 [/data/projects/nmigen_bugs/build/top.xdc:2]
Finished Parsing XDC File [/data/projects/nmigen_bugs/build/top.xdc]

dummy1 is merely used to work around / avoid #374.

Vivado fails later due to the design being empty, but I don't think that matters for this bug.

Full build folder: build.zip

[rroohhh]

Playing around a bit with vivado makes me come to the conclusion, that atleast '"{};$#[]\ are special characters and need to be escaped using \.

Furthermore there seem to be different rules for clock names, alluded to by this error message:

CRITICAL WARNING: [Vivado 12-2270] Clock names may not contain tcl special characters: '"{};$# - Skipping 'clk$1' [/data/projects/nmigen_bugs/build/top.xdc:2]

Which gets emitted when changing the constraint file to this:

create_clock -name clk\$1 -period 10.0 [get_nets \\clk\$1\ ]

[whitequark]

I -think- we can get away with using { } around net names and escaping only { and }. (Since we can't guarantee that we'll have a balanced number of those in a signal name, naturally.)

[rroohhh]

Atleast \ still needs escaping in the case of using { } around net names, atleast if it is the last character of the name.

[whitequark]

Yup that's true.

Regarding escaping itself, it'll have to be fully manual. You'd think Jinja2 will make it possible to customize the escaping engine, but nope! Hardcoded to HTML/XML.

[rroohhh]

Ouch, that is sad.