Can't compile slaspec when constraining a bit field that appears in the display section

[brendonky18]

Using the sleigh compiler from version 11.3.2, on the following minimal slaspec

define endian=big;
define alignment=1;

define space ram type=ram_space size=2 wordsize=1 default;

define space register type=register_space size=2;

# General purpose registers
define register offset=0x1000 size=1 [
	r
];


define token opcode (8)
	op = (0,3)
	imm =(4,7)
;
:zzz imm is op = 1 & imm=0 {}

I get the following error:

ERROR neuron.slaspec:24: Constraining currently undefined operand: imm (SleighCompile)  
ERROR Unrecoverable error(s), halting compilation (SleighCompile) ghidra.sleigh.grammar.BailoutException: Pattern equation parsing returned null
        at ghidra.sleigh.grammar.SleighCompiler.pequation(SleighCompiler.java:4372)
        at ghidra.sleigh.grammar.SleighCompiler.pequation(SleighCompiler.java:4192)
        at ghidra.sleigh.grammar.SleighCompiler.bitpattern(SleighCompiler.java:3617)
        at ghidra.sleigh.grammar.SleighCompiler.constructor(SleighCompiler.java:3469)
        at ghidra.sleigh.grammar.SleighCompiler.constructorlike(SleighCompiler.java:3028)
        at ghidra.sleigh.grammar.SleighCompiler.root(SleighCompiler.java:482)
        at ghidra.pcodeCPort.slgh_compile.SleighCompile.run_compilation(SleighCompile.java:1835)
        at ghidra.pcodeCPort.slgh_compile.SleighCompileLauncher.runMain(SleighCompileLauncher.java:217)
        at ghidra.pcodeCPort.slgh_compile.SleighCompileLauncher.launch(SleighCompileLauncher.java:50)
        at ghidra.GhidraLauncher.launch(GhidraLauncher.java:81)
        at ghidra.Ghidra.main(Ghidra.java:54)

If I change the constructor to be:

:zzz imm is op = 1 & imm {}

then it will build without an issue.

Why am I unable to constrain the value of imm?

[GhidorahRex]

I can't explain the why, but I do know that you can't simultaneously constrain a variable and use the variable in the operand section. A potential fix would be:

:zzz 0 is op=1 & imm {}

or (possibly preferable)

define token opcode (8)
	op = (0,3)
	imm =(4,7)
        imm2=(4,7)
;
:zzz imm is op = 1 & imm & imm2=0 {}

Since imm2 is the constraint and imm is the display, there's no conflict there.