Bug: Coalesce type inference returns Any instead of Integer in aggregate

[JPercival]

Summary

• Coalesce(R, 1) inside an aggregate with null starting value infers result type Any instead of Integer
• This causes the downstream Multiply to insert an unnecessary As(Integer) cast around the Coalesce result
• The correct behavior: Coalesce should compute its result type as the common type of concrete (non-Any/non-null) arguments

Reproduction

define Sequence: { 1, 2, 3 }
define Factorial:
  Sequence X
    aggregate R: Coalesce(R, 1) * X

The aggregate accumulator R starts as null (type Any). Coalesce(R, 1) resolves through generic operator overload matching, which unifies T to Any because the first arg has type Any. This gives the Coalesce a result type of Any, forcing the Multiply operator to insert an As(Integer) cast on its first operand.

Expected ELM: Multiply(Coalesce(QueryLetRef("R"), Literal(1)), AliasRef("X"))
Actual ELM: Multiply(As(Integer, Coalesce(QueryLetRef("R"), Literal(1))), AliasRef("X"))

Test

The included test (AggregateCoalesceTypeBugTest) demonstrates the bug by asserting that the first Multiply operand is wrapped in As — this assertion passes, confirming the unnecessary cast exists.

Test plan

• AggregateCoalesceTypeBugTest passes (demonstrates the bug)
• When fixed, the test assertion should be updated to assertIs<Coalesce>(firstOperand)

🤖 Generated with Claude Code

[github-actions]

Related Issues

The following open issues may be related to this PR:

Issue	Title	Score	Matched Terms
#1137	Inconsistent Casting in Unions	16	"cql define", literal, integer, cast, returns, define, operand, through, behavior, null, elm, value, type (path), bug (path), org (path), cql (path)
#1133	ToList is not implemented according to the spec	15.5	returns, com, define, code, operand, behavior, because, null, https, elm, value, operator (path), type (path), cqframework (path), java (path), src (path), bug (path), org (path), cql (path), test (path)
#734	Width allows Interval as a parameter	14	result, integer, returns, define, through, because, null, https, elm, generic, value, operator (path), type (path), operators (path), org (path), cql (path), tests (path)
#1400	patientBirthDatePropertyName marked as deprecated but still required for SystemFunctionResolver	13	non, instead, com, define, code, behavior, because, null, https, elm, cqframework (path), java (path), src (path), cql2elm (path), org (path), cql (path)
#840	ExpandValueSet is called aggressively	12.5	"cql define", instead, correct, overload, define, code, operand, because, elm, value, cql (path)

Tip: If this PR addresses any of these issues, please link them using Closes #NNN or Refs #NNN in the PR description.

[github-actions]

Formatting check succeeded!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.98%. Comparing base (e64b32f) to head (42adbb3).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1710      +/-   ##
============================================
- Coverage     65.68%   61.98%   -3.71%     
- Complexity     1645     3944    +2299     
============================================
  Files           481      210     -271     
  Lines         27890    20383    -7507     
  Branches       5553     3884    -1669     
============================================
- Hits          18320    12634    -5686     
+ Misses         7231     6139    -1092     
+ Partials       2339     1610     -729     

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