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Java: Make JumpStmt a proper superclass #8582

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Apr 25, 2022
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Java: Make JumpStmt a proper superclass #8582

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Java: Make `JumpStmt` a proper superclass
Marcono1234 Mar 28, 2022
348a186
Java: Make JumpStmt a concrete class again
Marcono1234 Apr 10, 2022
b21f077
Update java/ql/lib/semmle/code/java/Statement.qll
aschackmull Apr 25, 2022
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Java: Make JumpStmt a concrete class again 
Public abstract classes can be error-prone, when users unintentionally
implement a new subclass instead of refining the set of existing subclasses.
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@Marcono1234
Marcono1234 committed Apr 10, 2022
commit 348a186df89b0ffc0c9997a9e8a9af613bf1ab33
5 changes: 4 additions & 1 deletion java/ql/lib/semmle/code/java/Statement.qll
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Expand Up @@ -556,8 +556,11 @@ class ThrowStmt extends Stmt, @throwstmt {
override string getAPrimaryQlClass() { result = "ThrowStmt" }
}

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We generally try to avoid exposing public abstract classes like this, since subclassing using extends can lead to surprising results. It is better to define the union type explicitly:

Suggested change
private class JumpStmt_ = @breakstmt or @yieldstmt or @continuestmt;

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Good point, thanks! I have implemented your suggestion manually, and added a small comment explaining the rationale; hopefully that is alright.

A bit unrelated, but I have created a #8713 to discuss making implementing abstract classes less error-prone.

// Workaround to avoid having to make JumpStmt abstract
private class JumpStmt_ = @breakstmt or @yieldstmt or @continuestmt;

/** A `break`, `yield` or `continue` statement. */
abstract class JumpStmt extends Stmt {
class JumpStmt extends Stmt, JumpStmt_ {
/**
* Gets the labeled statement that this `break` or
* `continue` statement refers to, if any.
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