Ruby/QL: add discard predicates for locations

ql/ql/src/codeql_ql/ast/internal/TreeSitter.qll

@@ -9,6 +9,20 @@
 overlay[local]
 private predicate isOverlay() { databaseMetadata("isOverlay", "true") }
 
+/** Holds if `loc` is in the `file` and is part of the overlay base database. */
+overlay[local]
+private predicate discardableLocation(@file file, @location_default loc) {
+  not isOverlay() and locations_default(loc, file, _, _, _, _)
+}
+
+/** Holds if `loc` should be discarded, because it is part of the overlay base and is in a file that was also extracted as part of the overlay database. */
+overlay[discard_entity]
+private predicate discardLocation(@location_default loc) {
+  exists(@file file, string path | files(file, path) |
+    discardableLocation(file, loc) and overlayChangedFiles(path)
+  )
+}
+
 module QL {
   /** The base class for all AST nodes */
   class AstNode extends @ql_ast_node {

ruby/ql/lib/codeql/ruby/ast/internal/TreeSitter.qll

@@ -9,6 +9,20 @@
 overlay[local]
 private predicate isOverlay() { databaseMetadata("isOverlay", "true") }
 
+/** Holds if `loc` is in the `file` and is part of the overlay base database. */
+overlay[local]
+private predicate discardableLocation(@file file, @location_default loc) {
+  not isOverlay() and locations_default(loc, file, _, _, _, _)
+}
+
+/** Holds if `loc` should be discarded, because it is part of the overlay base and is in a file that was also extracted as part of the overlay database. */
+overlay[discard_entity]
+private predicate discardLocation(@location_default loc) {
+  exists(@file file, string path | files(file, path) |
+    discardableLocation(file, loc) and overlayChangedFiles(path)
+  )
+}
+
 module Ruby {
   /** The base class for all AST nodes */
   class AstNode extends @ruby_ast_node {

shared/tree-sitter-extractor/src/generator/mod.rs

@@ -51,9 +51,11 @@ pub fn generate(
 
     ql::write(
         &mut ql_writer,
-        &[ql::TopLevel::Predicate(
-            ql_gen::create_is_overlay_predicate(),
-        )],
+        &[
+            ql::TopLevel::Predicate(ql_gen::create_is_overlay_predicate()),
+            ql::TopLevel::Predicate(ql_gen::create_discardable_location_predicate()),
+            ql::TopLevel::Predicate(ql_gen::create_discard_location_predicate()),
+        ],
     )?;
 
     for language in languages {

shared/tree-sitter-extractor/src/generator/ql_gen.rs

@@ -396,6 +396,91 @@ pub fn create_discard_ast_node_predicate(ast_node_name: &str) -> ql::Predicate {
     }
 }
 
+pub fn create_discardable_location_predicate() -> ql::Predicate<'static> {
+    ql::Predicate {
+        name: "discardableLocation",
+        qldoc: Some(String::from(
+            "Holds if `loc` is in the `file` and is part of the overlay base database.",
+        )),
+        overridden: false,
+        is_private: true,
+        is_final: false,
+        overlay: Some(ql::OverlayAnnotation::Local),
+        return_type: None,
+        formal_parameters: vec![
+            ql::FormalParameter {
+                name: "file",
+                param_type: ql::Type::At("file"),
+            },
+            ql::FormalParameter {
+                name: "loc",
+                param_type: ql::Type::At("location_default"),
+            },
+        ],
+        body: ql::Expression::And(vec![
+            ql::Expression::Negation(Box::new(ql::Expression::Pred("isOverlay", vec![]))),
+            ql::Expression::Pred(
+                "locations_default",
+                vec![
+                    ql::Expression::Var("loc"),
+                    ql::Expression::Var("file"),
+                    ql::Expression::Var("_"),
+                    ql::Expression::Var("_"),
+                    ql::Expression::Var("_"),
+                    ql::Expression::Var("_"),
+                ],
+            ),
+        ]),
+    }
+}
+
+/// Creates a discard predicate for `@location_default` entities. This is necessary because the
+/// tree-sitter extractors use `*` IDs for locations, which means that locations don't get shared
+/// between the base and overlay databases.
+pub fn create_discard_location_predicate() -> ql::Predicate<'static> {
+    ql::Predicate {
+        name: "discardLocation",
+        qldoc: Some(String::from(
+            "Holds if `loc` should be discarded, because it is part of the overlay base \
+            and is in a file that was also extracted as part of the overlay database.",
+        )),
+        overridden: false,
+        is_private: true,
+        is_final: false,
+        overlay: Some(ql::OverlayAnnotation::DiscardEntity),
+        return_type: None,
+        formal_parameters: vec![ql::FormalParameter {
+            name: "loc",
+            param_type: ql::Type::At("location_default"),
+        }],
+        body: ql::Expression::Aggregate {
+            name: "exists",
+            vars: vec![
+                ql::FormalParameter {
+                    name: "file",
+                    param_type: ql::Type::At("file"),
+                },
+                ql::FormalParameter {
+                    name: "path",
+                    param_type: ql::Type::String,
+                },
+            ],
+            range: Some(Box::new(ql::Expression::Pred(
+                "files",
+                vec![ql::Expression::Var("file"), ql::Expression::Var("path")],
+            ))),
+            expr: Box::new(ql::Expression::And(vec![
+                ql::Expression::Pred(
+                    "discardableLocation",
+                    vec![ql::Expression::Var("file"), ql::Expression::Var("loc")],
+                ),
+                ql::Expression::Pred("overlayChangedFiles", vec![ql::Expression::Var("path")]),
+            ])),
+            second_expr: None,
+        },
+    }
+}
+
 /// Returns an expression to get a field that's defined as a column in the parent's table.
 ///
 /// # Arguments