Rust: Test dbscheme downgrade preservation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

rust/ql/upgrade-tests/66a489863649185f4a9770f894505803059a1312/README.md

@@ -1,6 +1,6 @@
 # Upgrade Regression Test for rust-analyzer 0.0.301 → 0.0.328
 
-This test verifies that the dbscheme upgrade script correctly preserves data when migrating databases from the old schema to the new schema.
+This test verifies that the dbscheme upgrade and downgrade scripts correctly preserve data when migrating databases between the old and new schemas.
 
 ## Running the test
 
@@ -16,10 +16,13 @@ This will:
 5. Restore your branch
 6. Upgrade the database to the new schema
 7. Verify that the old properties are still accessible via the new schema
+8. Downgrade the database back to the old schema
+9. Verify that the recovered old-schema properties still match
 
 ## Files
 
-- `old.ql` / `old.expected`: Query for the old schema (validates extraction)
+- `old.ql` / `old.expected`: Query for the old schema (validates extraction and downgrade)
 - `new.ql` / `new.expected`: Query for the new schema (validates upgrade preserved data)
+- `downgraded.ql` / `downgraded.expected`: Query for the downgraded old schema
 - `upgrade_shapes.rs`: Rust source containing test shapes for all affected schema elements
 - `run-test.sh`: Test runner script

rust/ql/upgrade-tests/66a489863649185f4a9770f894505803059a1312/downgraded.expected

@@ -0,0 +1,26 @@
+formatArgsArgName
+| upgrade_shapes.rs:22:37:22:41 | FormatArgsArg | upgrade_shapes.rs:22:37:22:37 | (no string representation) | upgrade_shapes.rs:22:41:22:41 | 1 | 37 |
+| upgrade_shapes.rs:22:44:22:48 | FormatArgsArg | upgrade_shapes.rs:22:44:22:44 | (no string representation) | upgrade_shapes.rs:22:48:22:48 | 2 | 44 |
+tryBlock
+| upgrade_shapes.rs:21:13:21:21 | { ... } |
+structFieldDefault
+| upgrade_shapes.rs:9:5:9:17 | field: u8 | upgrade_shapes.rs:9:17:9:17 | 1 |
+variantDiscriminant
+| upgrade_shapes.rs:13:5:13:9 | V | upgrade_shapes.rs:13:9:13:9 | 2 |
+metaPath
+| upgrade_shapes.rs:1:4:1:19 | Meta | allow |
+| upgrade_shapes.rs:2:4:2:32 | Meta | feature |
+| upgrade_shapes.rs:4:3:4:11 | Meta | path_meta |
+| upgrade_shapes.rs:5:3:5:15 | Meta | key_value |
+| upgrade_shapes.rs:6:3:6:18 | Meta | token_tree |
+| upgrade_shapes.rs:7:3:7:19 | Meta | path_meta |
+metaExpr
+| upgrade_shapes.rs:5:3:5:15 | Meta | upgrade_shapes.rs:5:15:5:15 | 1 |
+metaTokenTree
+| upgrade_shapes.rs:1:4:1:19 | Meta | upgrade_shapes.rs:1:9:1:19 | TokenTree |
+| upgrade_shapes.rs:2:4:2:32 | Meta | upgrade_shapes.rs:2:11:2:32 | TokenTree |
+| upgrade_shapes.rs:6:3:6:18 | Meta | upgrade_shapes.rs:6:13:6:18 | TokenTree |
+metaIsUnsafe
+| upgrade_shapes.rs:7:3:7:19 | Meta |
+traitAlias
+| upgrade_shapes.rs:16:1:18:12 | TraitAlias | upgrade_shapes.rs:16:7:16:11 | Alias | upgrade_shapes.rs:16:18:16:22 | ... | upgrade_shapes.rs:17:1:18:11 | WhereClause |

rust/ql/upgrade-tests/66a489863649185f4a9770f894505803059a1312/downgraded.ql

@@ -0,0 +1,56 @@
+import codeql.rust.elements
+
+private predicate inUpgradeShapesFile(Locatable loc) {
+  loc.getFile().getBaseName() = "upgrade_shapes.rs"
+}
+
+query predicate formatArgsArgName(FormatArgsArg arg, Name argName, Expr expr, int argNameColumn) {
+  inUpgradeShapesFile(arg) and
+  argName = arg.getName() and
+  expr = arg.getExpr() and
+  argNameColumn = argName.getLocation().getStartColumn()
+}
+
+query predicate tryBlock(BlockExpr block) {
+  inUpgradeShapesFile(block) and
+  block.isTry()
+}
+
+query predicate structFieldDefault(StructField field, Expr defaultVal) {
+  inUpgradeShapesFile(field) and
+  defaultVal = field.getDefault()
+}
+
+query predicate variantDiscriminant(Variant variant, Expr discriminant) {
+  inUpgradeShapesFile(variant) and
+  discriminant = variant.getDiscriminant()
+}
+
+query predicate metaPath(Meta meta, string pathText) {
+  inUpgradeShapesFile(meta) and
+  pathText = meta.getPath().getText()
+}
+
+query predicate metaExpr(Meta meta, Expr expr) {
+  inUpgradeShapesFile(meta) and
+  expr = meta.getExpr()
+}
+
+query predicate metaTokenTree(Meta meta, TokenTree tokenTree) {
+  inUpgradeShapesFile(meta) and
+  tokenTree = meta.getTokenTree()
+}
+
+query predicate metaIsUnsafe(Meta meta) {
+  inUpgradeShapesFile(meta) and
+  meta.isUnsafe()
+}
+
+query predicate traitAlias(
+  TraitAlias alias, Name name, TypeBoundList bounds, WhereClause whereClause
+) {
+  inUpgradeShapesFile(alias) and
+  name = alias.getName() and
+  bounds = alias.getTypeBoundList() and
+  whereClause = alias.getWhereClause()
+}

rust/ql/upgrade-tests/66a489863649185f4a9770f894505803059a1312/run-test.sh

@@ -7,6 +7,7 @@ set -euo pipefail
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 REPO_ROOT="$(git rev-parse --show-toplevel)"
 OLD_COMMIT="${OLD_COMMIT:-491c373e076}"  # origin/main at time of this upgrade
+OLD_DBSCHEME="rust/downgrades/109496fd2f20f28a35e50b110859e74882ee80d6/rust.dbscheme"
 
 cd "$REPO_ROOT"
 
@@ -64,4 +65,26 @@ codeql test run \
     --check-databases \
     "$SCRIPT_DIR/new.ql" "$@"
 
+echo "==> Downgrading dataset back to old schema..."
+codeql dataset upgrade "${DATASET_DIR[0]}" \
+    --allow-downgrades \
+    --search-path rust \
+    --target-dbscheme "$OLD_DBSCHEME"
+
+trap 'restore_ref' EXIT
+
+echo "==> Checking out old commit ($OLD_COMMIT) for downgrade verification..."
+git checkout --quiet "$OLD_COMMIT"
+git checkout --quiet "$ORIGINAL_REF" -- rust/ql/upgrade-tests codeql-workspace.yml
+
+echo "==> Running preservation test on downgraded dataset..."
+codeql test run \
+    --search-path . \
+    --dataset "${DATASET_DIR[0]}" \
+    --check-databases \
+    "$SCRIPT_DIR/downgraded.ql" "$@"
+
+restore_ref
+trap '' EXIT
+
 echo "==> All tests passed!"