Unexpected error for undefined variable

[obycode]

Instead of returning an analysis error for the undefined variable, we get a cost error. For example, if you try to deploy the following very simple contract:

foo

Instead of getting an analysis error about the unresolved variable, foo, the error reported by the miner when mining the deploy transaction is:

Aug 11 18:40:45.235019 INFO Runtime error in contract analysis for ST1PQHQKV0RJXZFY1DGX8MNSNYVE3VGZJSRTPGZGM.foo: Analysis(CheckError { err: CostComputationFailed("Error evaluating result of cost function ST000000000000000000002AMW42H.costs-3.cost_analysis_lookup_variable_depth: Arithmetic(\"log2 must be passed a positive integer\")\n Stack Trace: \n"), expressions: Some([SymbolicExpression { expr: Atom(ClarityName("foo")), id: 1 }]), diagnostic: Diagnostic { level: Error, message: "contract cost computation failed: Error evaluating result of cost function ST000000000000000000002AMW42H.costs-3.cost_analysis_lookup_variable_depth: Arithmetic(\"log2 must be passed a positive integer\")\n Stack Trace: \n", spans: [Span { start_line: 0, start_column: 0, end_line: 0, end_column: 0 }], suggestion: None } }), txid: e9f2d630e5ac44647a0a860dd720f11ae148e8a879dd134e1769199017015c50, AST rules: PrecheckSize

[obycode]

The problem arises from the cost check in TypeChecker::lookup_variable when it calls:

            runtime_cost(
                ClarityCostFunction::AnalysisLookupVariableDepth,
                self,
                context.depth,
            )?;

context.depth at this point is 0 because it is at the top-level, and this eventually reaches the log2, which causes this runtime error when passed 0.

[obycode]

Notes from discussion:

• When solving this, we must be careful to maintain the same costs as the current version, and validating that with a block replay
• This should be as simple as checking for context.depth == 0 and returning the error before the line mentioned above

[github-actions]

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