fix: infer LIMIT and OFFSET parameter types

[1fanwang]

Which issue does this PR close?

• Closes Placeholder datatype not inferred after LIMIT clause #15978.

Rationale for this change

Clients preparing queries need usable parameter types. Bare LIMIT/OFFSET parameters should default to Int64, but an explicit CAST($1 AS BIGINT) must leave its input unknown because the cast also accepts strings. Reporting Int64 incorrectly tells clients they must supply an integer.

Previously, optimized plans lost the bare parameter's default. Looking through every Int64 cast restored it but incorrectly typed explicit cast inputs.

What changes are included in this PR?

The analyzer records bare LIMIT/OFFSET parameter fields before coercion, preserving a type inferred elsewhere. Lookup does not unwrap user-written casts. This keeps explicit cast inputs unknown and allows Int32 binding followed by Int64 LIMIT coercion.

Coverage uses the existing parameter harnesses, optimizer integration, prepare.slt, and named/metadata DataFrame execution tests.

What is the testing strategy for this PR?

Testing Done

macOS arm64, Rust 1.98.1, with the repository's test-data submodules initialized.

Before the explicit-cast fix, the BIGINT cases failed on the production code from b66d80b. The regression then lived in core integration:

cargo test --profile ci -p datafusion --test core_integration test_limit_offset_parameters_leave_cast_inputs_unresolved -- --nocapture

explicit cast SQL: SELECT $1 AS value LIMIT CAST($1 AS BIGINT)
  left: {"$1": Some(Int64)}
 right: {"$1": None}

explicit cast SQL: SELECT $1 AS value FROM (VALUES (1), (2)) AS t(v) OFFSET CAST($1 AS BIGINT)
  left: {"$1": Some(Int64)}
 right: {"$1": None}

After the fix, the real CLI accepts string inputs in LIMIT, OFFSET and nested explicit casts, and paging returns the requested row:

cargo run --profile ci -p datafusion-cli -- --quiet -c "PREPARE page AS SELECT value FROM (VALUES (10), (20), (30)) AS t(value) ORDER BY value LIMIT \$1 OFFSET \$2; EXECUTE page(1, 1); DEALLOCATE page; PREPARE cast_page AS SELECT \$1 AS value LIMIT CAST(\$1 AS BIGINT); EXECUTE cast_page('1'); DEALLOCATE cast_page; PREPARE cast_offset AS SELECT \$1 AS value FROM (VALUES (1), (2)) AS t(v) OFFSET CAST(\$1 AS BIGINT); EXECUTE cast_offset('1'); DEALLOCATE cast_offset; PREPARE nested_cast AS SELECT \$1 AS value FROM (SELECT 1 LIMIT CAST(\$1 AS BIGINT)) AS t; EXECUTE nested_cast('1'); DEALLOCATE nested_cast;"

+-------+
| value |
+-------+
| 20    |
+-------+
+-------+
| value |
+-------+
| 1     |
+-------+
+-------+
| value |
+-------+
| 1     |
+-------+
+-------+
| value |
+-------+
| 1     |
+-------+

Are there any user-facing changes?

Bare LIMIT/OFFSET parameters default to Int64 before and after optimization. Explicit casts leave their input parameter types unresolved.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.72%. Comparing base (416002a) to head (68665c5).
⚠️ Report is 59 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/optimizer/src/analyzer/type_coercion.rs	88.88%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25364      +/-   ##
==========================================
+ Coverage   82.59%   82.72%   +0.12%     
==========================================
  Files        1145     1147       +2     
  Lines      444096   448217    +4121     
  Branches   444096   448217    +4121     
==========================================
+ Hits       366806   370781    +3975     
+ Misses      55021    54898     -123     
- Partials    22269    22538     +269     

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[kosiew]

@1fanwang,

Thanks for working on this. The change looks good overall. I left one non-blocking suggestion to add nested-query coverage for LIMIT/OFFSET parameter inference.

[jayzhan211]

Thanks @1fanwang , here are some suggestions

[jayzhan211]

Thanks @1fanwang , 1 suggestion

[jayzhan211]

The only request left: could we minimize the tests? Most of the 371 lines fit existing harnesses:

• metadata, type-conflict and field-metadata cases → ParameterTest / ParameterTestWithMetadata in datafusion/sql/tests/cases/params.rs (it checks types, binding and the Prepare fields)
• EXECUTE result cases → prepare.slt
• the analyzer→bind→optimize guard → datafusion/optimizer/tests/optimizer_integration.rs

Only the named-parameter (DataFrame API) case needs to stay in core_integration. While moving them, please drop the leftover println! calls

[kosiew]

@1fanwang,

Thanks for working on this. I found one issue with explicit BIGINT casts that needs to be addressed before this can merge.

[kosiew]

@1fanwang,

Thanks for the follow-up. The explicit BIGINT issue is fixed, and I don't see any remaining merge-blocking problems. I have one non-blocking cleanup suggestion below.

[kosiew]

There is still quite a bit of parameter-test setup duplicated here. Could you move the planning and binding assertions into the existing parameter harnesses where they fit, while keeping the analyzer/optimizer and execution-specific cases in coverage that actually exercises those phases?