Comparing a decimal with a negative scale to an integer literal panics in `unwrap_cast`

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
86/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
rust
Domain
databases

Research direction

Start in datafusion/expr-common/src/casts.rs at try_cast_numeric_literal, then follow its callers through try_cast_literal_to_type and unwrap_cast.rs. Reproduce the SQL query in a debug build of datafusion-cli and verify that negative-scale decimal comparisons no longer panic and leave unexpressible casts in place.

Written by the indexing model from the issue text.

Description

Describe the bug

try_cast_numeric_literal in datafusion/expr-common/src/casts.rs computes 10_i128.pow(scale as u32) for the target decimal type (and again for a decimal literal's own scale). A negative scale is cast to a huge u32 exponent, so the multiplication overflows and panics in debug builds (wraps in release builds).

The function is reached from the unwrap_cast expression simplifier whenever a cast to a decimal is compared with a numeric literal.

To Reproduce

Debug build of datafusion-cli:

SELECT arrow_cast(1, 'Decimal128(10, -2)') = 100;

thread 'main' panicked at library/core/src/num/mod.rs:475:5:
attempt to multiply with overflow

Backtrace goes through datafusion_expr_common::casts::try_cast_numeric_literal → try_cast_literal_to_type → unwrap_cast.rs.

Expected behavior

No panic. try_cast_literal_to_type already returns None for casts it cannot express; a negative scale (the decimal holds multiples of 10^-scale, so there is no integer 10^scale to rescale by) should be one of them, leaving the cast in place.

Additional context

Found while running a corpus of extreme-value literals against a debug build of datafusion-cli.

Dominant language
Rust
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