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Shared CFG: add defaulted getWhileElse/getForeachElse to AstSig #21931

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Shared CFG: add defaulted getWhileElse/getForeachElse to AstSig #21931

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61 changes: 58 additions & 3 deletions shared/controlflow/codeql/controlflow/ControlFlowGraph.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -211,6 +211,31 @@ signature module AstSig<LocationSig Location> {
*/
default AstNode getTryElse(TryStmt try) { none() }

/**
* Gets the `else` block of this `while` loop statement, if any.
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@hvitved hvitved Jun 8, 2026

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Suggested change
* Gets the `else` block of this `while` loop statement, if any.
* Gets the `else` block of `while` loop statement `loop`, if any.

*
* Only some languages (e.g. Python) support `while-else` constructs.
*/
default AstNode getWhileElse(WhileStmt loop) { none() }
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@aschackmull aschackmull Jun 8, 2026

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Let's stick to just one new predicate

Suggested change
default AstNode getWhileElse(WhileStmt loop) { none() }
default AstNode getLoopElse(LoopStmt loop) { none() }

The semantics of a loop-else block is mainly related to whether the loop exits via its condition or a break, so it's not really tied to the specifics of while vs. foreach.


/**
* Gets the `else` block of this `foreach` loop statement, if any.
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@hvitved hvitved Jun 8, 2026

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Suggested change
* Gets the `else` block of this `foreach` loop statement, if any.
* Gets the `else` block of `foreach` loop statement `loop`, if any.

*
* Only some languages (e.g. Python) support `for-else` constructs.
*/
default AstNode getForeachElse(ForeachStmt loop) { none() }

/**
* Gets the type expression of this catch clause, if any.
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Suggested change
* Gets the type expression of this catch clause, if any.
* Gets the type expression of catch clause `catch`, if any.

*
* In Python, the catch type is a runtime-evaluated expression
* (e.g. `except SomeException:` where `SomeException` is an
* arbitrary expression). For languages where the catch type is
* statically resolved, this defaults to `none()` and no CFG node
* is created.
*/
default Expr getCatchType(CatchClause catch) { none() }
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@aschackmull aschackmull Jun 8, 2026

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This is unrelated to the PR description - was this meant to go in a different PR?

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@aschackmull aschackmull Jun 8, 2026

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Also, unless absolutely necessary, I don't think this should be a point of parameterisation - rather, I think we ought to be able to come up with a CFG for catch that solves the needs of all languages. We should probably discuss this offline and put a fix in a different PR when we agree on the solution.


/** A catch clause in a try statement. */
class CatchClause extends AstNode {
/** Gets the variable declared by this catch clause. */
Expand Down Expand Up @@ -1549,19 +1574,32 @@ module Make0<LocationSig Location, AstSig<Location> Ast> {
n2.isBefore(loopstmt.getBody())
or
n1.isAfterFalse(cond) and
n2.isAfter(loopstmt)
(
n2.isBefore(getWhileElse(loopstmt))
or
not exists(getWhileElse(loopstmt)) and n2.isAfter(loopstmt)
)
or
n1.isAfter(loopstmt.getBody()) and
n2.isAdditional(loopstmt, loopHeaderTag())
)
or
exists(WhileStmt whilestmt |
n1.isAfter(getWhileElse(whilestmt)) and
n2.isAfter(whilestmt)
)
or
exists(ForeachStmt foreachstmt |
n1.isBefore(foreachstmt) and
n2.isBefore(foreachstmt.getCollection())
or
n1.isAfterValue(foreachstmt.getCollection(),
any(EmptinessSuccessor t | t.getValue() = true)) and
n2.isAfter(foreachstmt)
(
n2.isBefore(getForeachElse(foreachstmt))
or
not exists(getForeachElse(foreachstmt)) and n2.isAfter(foreachstmt)
)
or
n1.isAfterValue(foreachstmt.getCollection(),
any(EmptinessSuccessor t | t.getValue() = false)) and
Expand All @@ -1574,10 +1612,17 @@ module Make0<LocationSig Location, AstSig<Location> Ast> {
n2.isAdditional(foreachstmt, loopHeaderTag())
or
n1.isAdditional(foreachstmt, loopHeaderTag()) and
n2.isAfter(foreachstmt)
(
n2.isBefore(getForeachElse(foreachstmt))
or
not exists(getForeachElse(foreachstmt)) and n2.isAfter(foreachstmt)
)
or
n1.isAdditional(foreachstmt, loopHeaderTag()) and
n2.isBefore(foreachstmt.getVariable())
or
n1.isAfter(getForeachElse(foreachstmt)) and
n2.isAfter(foreachstmt)
)
or
exists(ForStmt forstmt, PreControlFlowNode condentry |
Expand Down Expand Up @@ -1671,6 +1716,16 @@ module Make0<LocationSig Location, AstSig<Location> Ast> {
exists(CatchClause catchclause |
exists(MatchingSuccessor t |
n1.isBefore(catchclause) and
(
n2.isBefore(getCatchType(catchclause))
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@hvitved hvitved Jun 8, 2026

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t is unbound in this disjunct.

or
not exists(getCatchType(catchclause)) and n2.isAfterValue(catchclause, t)
) and
if Input1::catchAll(catchclause) then t.getValue() = true else any()
)
or
exists(MatchingSuccessor t |
n1.isAfter(getCatchType(catchclause)) and
n2.isAfterValue(catchclause, t) and
if Input1::catchAll(catchclause) then t.getValue() = true else any()
)
Expand Down
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