Diagnostics: inline-record mutability coercion gives no reason, and `throw` in `finally` warns about unreachable code

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4/5
預估耗時
3-5 天
新手友好度
38/100
Issue 類型
缺陷
描述清晰度
基本清楚
活躍度
活躍
技術堆疊
ocaml
領域
compilers, developer-experience

研究方向

The throw-in-finally case points to compiler/ml/typecore.ml around lines 2920-2922, where the finally block is typed as a statement; check how warning 21 is raised for non-returning statements. The inline-record coercion error is reached through a subtype path the payload does not name, so locate it by searching for the existing plain-record mutability explanation and compare the two. Run the two snippets from the issue to confirm the wrong output, and count done as the mutable-field explanation appearing for inline records and warning 21 no longer firing for throw in finally.

由索引模型根據 Issue 內容生成。

描述

Found by differential semantic drift analysis from b123b7c3 to c10223e8.

What is broken

  • Coercion into an inline record with a mutable field gives no reason (#9086). The coercion is now rejected, correctly:

    type v1 = A({x: float})
type v2 = A({mutable x: float})
let a: v1 = A({x: 0.})
let b = (a :> v2)

    The error is only Type v1 is not a subtype of v2. For a field of a plain record type ({r: r1} into {r: r2}) the error explains: "The field x is mutable in record r2, but not in record r1. A coercion can't make a field writable."

  • throw in finally gives warning 21 (#8931):

    exception B
let k = () => try { 1 } finally { throw(B) }

    Warning 21: "This statement does not continue execution; following code is unreachable." No code follows the throw; the generated JavaScript is correct. The finally block is typed as a statement (typecore.ml L2920-L2922), and a non-returning statement triggers this warning.

Possible cause (speculation only)

The inline-record path reports the subtype failure before reaching the field comparison that produces the explanation for plain records.

🤖 Generated with Claude Code

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