feat: add db_get_dependents for reverse dependency lookup

Author: AnmiTaliDev

ROADMAP.md

@@ -1,41 +1,5 @@
 # libAPG Roadmap
 
-## v1.1 (current)
-
-- [x] Package metadata parsing (JSON)
-- [x] File, script, and config installation
-- [x] Installed package database (LMDB)
-- [x] Checksums: CRC32, MD5, SHA-256
-- [x] Package signing: PGP (gpgme) / libsodium
-- [x] Hardware-accelerated SHA-256 (x86_64 SHA-NI, AArch64 crypto, RISC-V Zknh)
-- [x] Optimized assembly for CRC32 and MD5 on all three architectures
-
-## v1.2 — Dependencies and conflicts
-
-- [x] Dependency resolver (graph, topological sort)
-- [x] Conflict and circular dependency detection at install time
-- [x] `provides` / `replaces` support during resolution
-- [x] API to query: what installing package X will break
-
-## v1.3 — Transactions and rollback
-
-- [x] Rollback on post-install script failure
-- [x] Transaction journal in the database
-
-## v1.4 — Database API
-
-- [x] Public API for third-party tools to register installed packages
-- [x] Conflict-free parallel installs: no "package not installed" or "file busy" errors when multiple tools write to the DB simultaneously
-- [x] Lock-free read path for queries (list, search, get)
-- [x] Hooks: pre/post DB write callbacks for tools like custom package helpers
-
-## v1.5 — Security
-
-- [x] Trust chain verification (keyring)
-- [x] Install policies: reject unsigned packages, trusted key list
-- [x] Sandboxed execution of install scripts (seccomp / namespaces)
-- [x] Audit log of all package operations
-
 ## v2.0 — Stable public API
 
 - [ ] ABI stabilization and documentation

include/apg/db.h

@@ -130,3 +130,20 @@ struct package **db_list(struct db_handle *db, int *count);
  *         owns @p path. Caller must free() the returned string.
  */
 char *db_owner(struct db_handle *db, const char *path);
+
+/**
+ * @brief Find all installed packages that depend on a given package.
+ *
+ * Checks direct dependencies and virtual names listed in the target package's
+ * @c provides field, so removing a provider is flagged even when dependents
+ * name the virtual package rather than the real one.
+ *
+ * @param db       Database handle.
+ * @param pkg_name Name of the package being queried.
+ * @param count    Output parameter set to the number of dependents found.
+ * @return Heap-allocated array of heap-allocated package name strings, or NULL
+ *         on failure. Caller must free() each element and the array itself.
+ *         @p *count is set to 0 when no dependents are found.
+ */
+char **db_get_dependents(struct db_handle *db, const char *pkg_name,
+                         int *count);

meson.build

@@ -20,6 +20,7 @@ libapg_sources = files(
   'src/db/owner.c',
   'src/db/journal.c',
   'src/db/audit.c',
+  'src/db/dependents.c',
   'src/json.c',
   'src/graph/graph.c',
   'src/graph/resolve.c',

src/db/dependents.c

@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-3.0-only
+// SPDX-FileCopyrightText: 2026 AnmiTaliDev <anmitalidev@nuros.org>
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "../../include/apg/db.h"
+#include "../../include/apg/package.h"
+#include "../../include/apg/version.h"
+
+static bool
+names_match(const char *needle, const char *pkg_name,
+            const struct str_list *provides)
+{
+    if (strcmp(needle, pkg_name) == 0)
+        return true;
+    for (int i = 0; i < provides->count; i++)
+        if (strcmp(needle, provides->items[i]) == 0)
+            return true;
+    return false;
+}
+
+char **
+db_get_dependents(struct db_handle *db, const char *pkg_name, int *count)
+{
+    *count = 0;
+    if (!db || !pkg_name)
+        return NULL;
+
+    struct str_list provides = {0};
+    struct package *target = db_get(db, pkg_name);
+    if (target && target->meta)
+        provides = target->meta->provides;
+
+    int all_count = 0;
+    struct package **all = db_list(db, &all_count);
+    if (!all)
+    {
+        package_free(target);
+        return NULL;
+    }
+
+    int cap = 8;
+    char **result = malloc(cap * sizeof(char *));
+    if (!result)
+        goto out;
+
+    for (int i = 0; i < all_count; i++)
+    {
+        struct package *p = all[i];
+        if (!p->meta || !p->meta->name)
+            continue;
+        if (strcmp(p->meta->name, pkg_name) == 0)
+            continue;
+
+        bool found = false;
+        const struct dep_constraint_list *deps = &p->meta->dependencies;
+        for (int j = 0; j < deps->count && !found; j++)
+            found = names_match(deps->items[j].name, pkg_name, &provides);
+
+        if (!found)
+            continue;
+
+        if (*count == cap)
+        {
+            cap *= 2;
+            char **tmp = realloc(result, cap * sizeof(char *));
+            if (!tmp)
+                break;
+            result = tmp;
+        }
+        result[(*count)++] = strdup(p->meta->name);
+    }
+
+out:
+    for (int i = 0; i < all_count; i++)
+        package_free(all[i]);
+    free(all);
+    package_free(target);
+    return result;
+}