Error when applying pattern

[franzmach]

Hello, I have a slightly difficult use case of egg and I'm not quite getting it right.This is the error:

[2023-12-18T16:37:48Z DEBUG egg::machine] Compiled [Var("?0"), Var("?1"), Var("?2"), ENode(Term { term_id: 0, children: [1, 2] })] to Program { instructions: [Bind { node: Term { term_id: 0, children: [0, 0] }, i: Reg(0), out: Reg(1) }], subst: {?1: 1, ?2: 2} }
[2023-12-18T16:37:48Z DEBUG egg::machine] Compiled [Var("?0"), Var("?1"), ENode(Term { term_id: 0, children: [0, 1] }), Var("?2"), ENode(Term { term_id: 0, children: [0, 3] })] to Program { instructions: [Bind { node: Term { term_id: 0, children: [0, 0] }, i: Reg(0), out: Reg(1) }], subst: {?0: 1, ?2: 2} }
[2023-12-18T16:37:48Z INFO  egg::egraph] REBUILT! in 0.000s
      Old: hc size 6, eclasses: 6
      New: hc size 6, eclasses: 6
      unions: 0, trimmed nodes: 0
[2023-12-18T16:37:48Z DEBUG egg::machine] Compiled [ENode(Var { index: 0 }), ENode(Var { index: 1 }), ENode(Var { index: 2 }), ENode(Term { term_id: 0, children: [1, 2] })] to Program { instructions: [Lookup { term: [ENode(Var { index: 2 }), ENode(Var { index: 1 }), ENode(Term { term_id: 0, children: [1, 0] })], i: Reg(0) }], subst: {} }
[2023-12-18T16:37:48Z DEBUG egg::machine] Compiled [ENode(Var { index: 0 }), ENode(Var { index: 1 }), ENode(Term { term_id: 0, children: [0, 1] }), ENode(Var { index: 2 }), ENode(Term { term_id: 0, children: [0, 3] })] to Program { instructions: [Lookup { term: [ENode(Var { index: 2 }), ENode(Var { index: 0 }), ENode(Term { term_id: 0, children: [1, 0] })], i: Reg(0) }], subst: {} }
[2023-12-18T16:37:48Z INFO  egg::egraph] REBUILT! in 0.000s
      Old: hc size 6, eclasses: 6
      New: hc size 6, eclasses: 6
      unions: 0, trimmed nodes: 0
[2023-12-18T16:37:48Z INFO  egg::run] 
    Iteration 0
[2023-12-18T16:37:48Z INFO  egg::run] Search time: 0.000023746
[2023-12-18T16:37:48Z DEBUG egg::run] Applying simpl 3 times

Var '?1=?1' not found in {?0: 0, ?2: 1}
thread 'dev::umb_tree::tests::does_simplify' panicked at /home/olof/.cargo/registry/src/index.crates.io-6f17d22bba15001f/egg-0.9.5/src/pattern.rs:403:40:
Var '?1=?1' not found in {?0: 0, ?2: 1}

As I've understood it, the pattern matches on something and then the substitution generated doesn't include substitutions for all of the variables in the pattern.

My applier merely checks if the substitution is valid and then forwards the application to a Pattern. It doesn't change the substitution found in any way. The searcher is also a Pattern.
How could my error occur? All the pattern matching and application is in the end handled by the Pattern struct?
Edit:
The error is probably the other way around? That the substitution includes variables not present in the search pattern which probably happens due to me incorrectly parsing the expressions into patterns?
Edit 2:
Nope, parsing is correct and it probably isn't the other way around. But for some reason it still doesn't work. Could someone explain the error message?
Edit 3:
There was indeed an parse error.
Forgot to add the head node when parsing

[mwillsey]

Seems like you fixed it!