feat(registry): accept v1 (bare array) installed.json

Composer's FilesystemRepository::initialize branches on
isset($data['packages']) — object form is v2, bare array is v1 —
and treats dev-package-names/dev as optional. Mirror that in
InstalledPackages::read so Mozart consumes shared .test fixtures
(which use v1) without harness preprocessing, and so installs over
v1-era vendor directories keep working. Drop the v1→v2 wrapper
that was added to mozart-test-harness for the same reason.

Removes #[ignore] from update_to_empty_from_locked (2/187 green).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

3 files changed, 111 insertions, 6 deletions

diff --git a/crates/mozart-registry/src/installed.rs b/crates/mozart-registry/src/installed.rs
index 7543b0e..6e8e0ac 100644
--- a/crates/mozart-registry/src/installed.rs
+++ b/crates/mozart-registry/src/installed.rs
@@ -70,14 +70,67 @@ impl InstalledPackages {
 
     /// Read installed.json from `vendor/composer/installed.json`.
     /// If the file does not exist, returns an empty registry.
+    ///
+    /// Accepts both Composer formats, mirroring `FilesystemRepository::initialize`:
+    /// - **v2** — object with a `packages` array, plus optional `dev-package-names`/`dev`
+    ///   (the shape Composer 2.x writes).
+    /// - **v1** — bare array of package entries (older shape; still legal input).
     pub fn read(vendor_dir: &Path) -> anyhow::Result<InstalledPackages> {
         let path = vendor_dir.join("composer/installed.json");
         if !path.exists() {
             return Ok(InstalledPackages::new());
         }
         let content = fs::read_to_string(&path)?;
-        let installed: InstalledPackages = serde_json::from_str(&content)?;
-        Ok(installed)
+        Self::from_json_str(&content)
+    }
+
+    /// Parse an installed.json document. See [`Self::read`] for the accepted shapes.
+    pub fn from_json_str(content: &str) -> anyhow::Result<InstalledPackages> {
+        use anyhow::{Context, anyhow};
+
+        let value: serde_json::Value =
+            serde_json::from_str(content).context("invalid installed.json")?;
+
+        match value {
+            serde_json::Value::Object(mut obj) => {
+                let packages_value = obj.remove("packages").ok_or_else(|| {
+                    anyhow!("Could not parse package list from installed.json (missing `packages`)")
+                })?;
+                let packages: Vec<InstalledPackageEntry> =
+                    serde_json::from_value(packages_value)
+                        .context("invalid `packages` array in installed.json")?;
+
+                let dev_package_names: Vec<String> = match obj.remove("dev-package-names") {
+                    Some(v) => serde_json::from_value(v)
+                        .context("invalid `dev-package-names` in installed.json")?,
+                    None => Vec::new(),
+                };
+                let dev: bool = match obj.remove("dev") {
+                    Some(v) => {
+                        serde_json::from_value(v).context("invalid `dev` flag in installed.json")?
+                    }
+                    None => true,
+                };
+
+                Ok(InstalledPackages {
+                    packages,
+                    dev_package_names,
+                    dev,
+                })
+            }
+            serde_json::Value::Array(_) => {
+                let packages: Vec<InstalledPackageEntry> = serde_json::from_value(value)
+                    .context("invalid v1 installed.json package array")?;
+                Ok(InstalledPackages {
+                    packages,
+                    dev_package_names: Vec::new(),
+                    dev: true,
+                })
+            }
+            _ => Err(anyhow!(
+                "Could not parse package list from installed.json (expected object or array)"
+            )),
+        }
     }
 
     /// Write installed.json to `vendor/composer/installed.json`.
@@ -206,6 +259,56 @@ mod tests {
     }
 
     #[test]
+    fn test_reads_v2_object_form() {
+        let json = r#"{
+            "packages": [
+                {"name": "a/a", "version": "1.0.0"}
+            ],
+            "dev-package-names": ["a/a"],
+            "dev": false
+        }"#;
+        let installed = InstalledPackages::from_json_str(json).unwrap();
+        assert_eq!(installed.packages.len(), 1);
+        assert_eq!(installed.packages[0].name, "a/a");
+        assert_eq!(installed.dev_package_names, vec!["a/a".to_string()]);
+        assert!(!installed.dev);
+    }
+
+    #[test]
+    fn test_reads_v1_array_form() {
+        // Composer 1.x / fixture-style: bare array of packages.
+        // FilesystemRepository::initialize accepts this; so must Mozart.
+        let json = r#"[
+            {"name": "a/a", "version": "1.0.0"},
+            {"name": "b/b", "version": "2.0.0"}
+        ]"#;
+        let installed = InstalledPackages::from_json_str(json).unwrap();
+        assert_eq!(installed.packages.len(), 2);
+        assert_eq!(installed.packages[0].name, "a/a");
+        assert_eq!(installed.packages[1].name, "b/b");
+        assert!(installed.dev_package_names.is_empty());
+        assert!(installed.dev);
+    }
+
+    #[test]
+    fn test_v2_defaults_when_optional_fields_missing() {
+        let json = r#"{"packages": []}"#;
+        let installed = InstalledPackages::from_json_str(json).unwrap();
+        assert!(installed.packages.is_empty());
+        assert!(installed.dev_package_names.is_empty());
+        assert!(installed.dev);
+    }
+
+    #[test]
+    fn test_rejects_non_object_non_array() {
+        let err = InstalledPackages::from_json_str("\"oops\"").unwrap_err();
+        assert!(
+            err.to_string().contains("expected object or array"),
+            "{err}"
+        );
+    }
+
+    #[test]
     fn test_is_installed_case_insensitive() {
         let mut installed = InstalledPackages::new();
         installed.upsert(make_entry("Monolog/Monolog", "3.8.0"));
diff --git a/crates/mozart-test-harness/src/runner.rs b/crates/mozart-test-harness/src/runner.rs
index e041cd7..cefd50f 100644
--- a/crates/mozart-test-harness/src/runner.rs
+++ b/crates/mozart-test-harness/src/runner.rs
@@ -20,6 +20,11 @@ pub struct RunResult {
 
 /// Set up a temp project from the parsed test, invoke `mozart` with the
 /// `--RUN--` command, and capture the result.
+///
+/// `--INSTALLED--` is written verbatim to `vendor/composer/installed.json`.
+/// Composer's fixtures use the v1 plain-array shape (`[{...}]`), which
+/// `FilesystemRepository::initialize` accepts alongside the v2 object shape;
+/// Mozart's reader is expected to do the same. Do not pre-wrap here.
 pub fn run_test(test: &ParsedTest, mozart_bin: &Path) -> Result<RunResult> {
     let working_dir = TempDir::new().context("failed to create tempdir")?;
     let root = working_dir.path();
diff --git a/crates/mozart/tests/installer.rs b/crates/mozart/tests/installer.rs
index a0e3f25..0520108 100644
--- a/crates/mozart/tests/installer.rs
+++ b/crates/mozart/tests/installer.rs
@@ -766,10 +766,7 @@ installer_fixture!(
     ignore = "mozart binary cannot yet run this fixture"
 );
 installer_fixture!(update_to_empty_from_blank);
-installer_fixture!(
-    update_to_empty_from_locked,
-    ignore = "mozart binary cannot yet run this fixture"
-);
+installer_fixture!(update_to_empty_from_locked);
 installer_fixture!(
     update_with_all_dependencies,
     ignore = "mozart binary cannot yet run this fixture"