Java: Add abstraction for discardable locatables

java/ql/lib/semmle/code/java/Expr.qll

@@ -2704,13 +2704,4 @@ class RecordPatternExpr extends Expr, @recordpatternexpr {
 }
 
 overlay[local]
-private predicate discardableExpr(string file, @expr e) {
-  not isOverlay() and
-  file = getRawFile(e)
-}
-
-/** Discard base expressions in files fully extracted in the overlay. */
-overlay[discard_entity]
-private predicate discardExpr(@expr e) {
-  exists(string file | discardableExpr(file, e) and extractedInOverlay(file))
-}
+private class DiscardableExpr extends DiscardableLocatable, @expr { }

java/ql/lib/semmle/code/java/Javadoc.qll

@@ -199,13 +199,4 @@ class KtCommentSection extends @ktcommentsection {
 }
 
 overlay[local]
-private predicate discardableJavadoc(string file, @javadoc d) {
-  not isOverlay() and
-  exists(@member m | file = getRawFile(m) and hasJavadoc(m, d))
-}
-
-/** Discard javadoc entities in files fully extracted in the overlay. */
-overlay[discard_entity]
-private predicate discardJavadoc(@javadoc d) {
-  exists(string file | discardableJavadoc(file, d) and extractedInOverlay(file))
-}
+private class DiscardableJavadoc extends DiscardableLocatable, @javadoc { }

java/ql/lib/semmle/code/java/Member.qll

@@ -906,31 +906,11 @@ class ExtensionMethod extends Method {
 }
 
 overlay[local]
-private predicate discardableMethod(string file, @method m) {
-  not isOverlay() and
-  file = getRawFile(m) and
-  exists(@classorinterface c | methods(m, _, _, _, c, _) and isAnonymClass(c, _))
-}
-
-/** Discard base methods on anonymous classes in files fully extracted in the overlay. */
-overlay[discard_entity]
-private predicate discardAnonMethod(@method m) {
-  exists(string file | discardableMethod(file, m) and extractedInOverlay(file))
+private class DiscardableAnonymousMethod extends DiscardableLocatable, @method {
+  DiscardableAnonymousMethod() {
+    exists(@classorinterface c | methods(this, _, _, _, c, _) and isAnonymClass(c, _))
+  }
 }
 
 overlay[local]
-private predicate discardableBaseMethod(string file, @method m) {
-  not isOverlay() and
-  file = getRawFile(m)
-}
-
-overlay[local]
-private predicate usedOverlayMethod(@method m) { isOverlay() and methods(m, _, _, _, _, _) }
-
-/** Discard base methods in files fully extracted in the overlay that were not extracted in the overlay. */
-overlay[discard_entity]
-private predicate discardMethod(@method m) {
-  exists(string file |
-    discardableBaseMethod(file, m) and extractedInOverlay(file) and not usedOverlayMethod(m)
-  )
-}
+private class DiscardableMethod extends DiscardableReferableLocatable, @method { }

java/ql/lib/semmle/code/java/Overlay.qll

@@ -35,3 +35,46 @@ predicate extractedInOverlay(string file) {
   // ignore skeleton extracted files in the overlay
   exists(@locatable l | numlines(l, _, _, _) and file = getRawFile(l))
 }
+
+/**
+ * A `@locatable` that should be discarded in the base variant if its file is
+ * extracted in the overlay variant.
+ */
+overlay[local]
+abstract class DiscardableLocatable extends @locatable {
+  /** Gets the raw file for a locatable in base. */
+  string getRawFileInBase() { not isOverlay() and result = getRawFile(this) }
+
+  /** Gets a textual representation of this discardable locatable. */
+  string toString() { none() }
+}
+
+overlay[discard_entity]
+private predicate discardLocatable(@locatable el) {
+  extractedInOverlay(el.(DiscardableLocatable).getRawFileInBase())
+}
+
+/**
+ * A `@locatable` that should be discarded in the base variant if its file is
+ * extracted in the overlay variant and it is itself not extracted in the
+ * overlay, that is, it is deleted in the overlay.
+ */
+overlay[local]
+abstract class DiscardableReferableLocatable extends @locatable {
+  /** Gets the raw file for a locatable in base. */
+  string getRawFileInBase() { not isOverlay() and result = getRawFile(this) }
+
+  /** Holds if the locatable exists in the overlay. */
+  predicate existsInOverlay() { isOverlay() and exists(this) }
+
+  /** Gets a textual representation of this discardable locatable. */
+  string toString() { none() }
+}
+
+overlay[discard_entity]
+private predicate discardReferableLocatable(@locatable el) {
+  exists(DiscardableReferableLocatable drl | drl = el |
+    extractedInOverlay(drl.getRawFileInBase()) and
+    not drl.existsInOverlay()
+  )
+}

java/ql/lib/semmle/code/java/Statement.qll

@@ -990,13 +990,4 @@ class SuperConstructorInvocationStmt extends Stmt, ConstructorCall, @superconstr
 }
 
 overlay[local]
-private predicate discardableStmt(string file, @stmt s) {
-  not isOverlay() and
-  file = getRawFile(s)
-}
-
-/** Discard base statements in files fully extracted in the overlay. */
-overlay[discard_entity]
-private predicate discardStmt(@stmt s) {
-  exists(string file | discardableStmt(file, s) and extractedInOverlay(file))
-}
+private class DiscardableStmt extends DiscardableLocatable, @stmt { }

java/ql/lib/semmle/code/java/Variable.qll

@@ -136,13 +136,4 @@ class Parameter extends Element, @param, LocalScopeVariable {
 }
 
 overlay[local]
-private predicate discardableLocalVarDecl(string file, @localscopevariable l) {
-  not isOverlay() and
-  file = getRawFile(l)
-}
-
-/** Discard base local scoped variables in files fully extracted in the overlay. */
-overlay[discard_entity]
-private predicate discardLocalVarDecl(@localscopevariable l) {
-  exists(string file | discardableLocalVarDecl(file, l) and extractedInOverlay(file))
-}
+private class DiscardableLocalScopeVariable extends DiscardableLocatable, @localscopevariable { }