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C/C++ Overlay: Preserve entities that have at least one location in an unchanged file

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Previously, an entity would be discarded if it had any location in a changed
file. This caused issues for entities with multiple declaration entries, such
as extern variables declared in one file and defined in another.

For example, given:
  // a.c (changed)       // b.c (unchanged)
  extern int x;          int x;

The variable `x` should be preserved because it has a location in the
unchanged file b.c, even though it also has a location in the changed file a.c.
This commit is contained in:
idrissrio
2025-11-26 13:05:12 +01:00
parent 39136f3827
commit 6c09325838
1 changed files with 40 additions and 16 deletions
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56
cpp/ql/lib/semmle/code/cpp/internal/Overlay.qll
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@@ -16,25 +16,49 @@ private string getLocationFilePath(@location_default loc) {
exists(@file file | locations_default(loc, file, _, _, _, _) | files(file, result)) exists(@file file | locations_default(loc, file, _, _, _, _) | files(file, result))
} }
/**
* Gets the file path for an element in the base variant.
*/
overlay[local] overlay[local]
private string getElementPathInBase(@element e) { private class DiscardableEntityBase extends @element {
not isOverlay() and /** Gets the path to the file in which this element occurs. */
exists(@location_default loc | abstract string getFilePath();
// Direct location (declarations)
var_decls(e, _, _, _, loc) /** Holds if this element exists in the base variant. */
or predicate existsInBase() { not isOverlay() }
// Indirect location (entities)
exists(@var_decl vd | var_decls(vd, e, _, _, _) | var_decls(vd, _, _, _, loc)) /** Gets a textual representation of this discardable element. */
| string toString() { none() }
result = getLocationFilePath(loc)
)
} }
/** /**
* Discard any element from the base that is in a changed file. * Discard an entity from the base if all its locations are in changed files.
* Entities with at least one location in an unchanged file are kept.
*/ */
overlay[discard_entity] overlay[discard_entity]
private predicate discardElement(@element e) { overlayChangedFiles(getElementPathInBase(e)) } private predicate discardEntity(@element e) {
e =
any(DiscardableEntityBase de |
de.existsInBase() and
overlayChangedFiles(de.getFilePath()) and
// Only discard if ALL file paths are in changed files
forall(string path | path = de.getFilePath() | overlayChangedFiles(path))
)
}
/** A discardable variable declaration entry. */
overlay[local]
private class DiscardableVarDecl extends DiscardableEntityBase instanceof @var_decl {
override string getFilePath() {
exists(@location_default loc | var_decls(this, _, _, _, loc) |
result = getLocationFilePath(loc)
)
}
}
/** A discardable variable. */
overlay[local]
private class DiscardableVariable extends DiscardableEntityBase instanceof @variable {
override string getFilePath() {
exists(@var_decl vd, @location_default loc | var_decls(vd, this, _, _, loc) |
result = getLocationFilePath(loc)
)
}
}