[M6] resolver: pkg-config probe + codegen for PkgConfig

src/linkdb/database.cpp

@@ -64,6 +64,7 @@ auto Database::resolve(const std::string& package, const std::string& version,
             .find_package = row.find_package,
             .targets = row.targets,
             .source = row.source,
+            .pkg_config_module = row.pkg_config_module,
         };
     }
     return std::unexpected(util::Error{

src/linkdb/linkdb.cppm

@@ -15,6 +15,16 @@ struct Recipe {
     std::vector<std::string> targets; // post-substitution
     std::string source; // 'curated' | 'manual' | etc.
 
+    // When set, the dep is consumed via PkgConfig instead of a normal
+    // find_package. Codegen emits
+    //   find_package(PkgConfig REQUIRED)
+    //   pkg_check_modules(<UPPER> REQUIRED IMPORTED_TARGET <pkg_config_module>)
+    // and the recipe's `targets` list holds the synthesized
+    // PkgConfig::<UPPER> entries. `find_package` for these recipes is
+    // the literal string "PkgConfig REQUIRED" — kept consistent so
+    // overlay rows don't need a sentinel.
+    std::optional<std::string> pkg_config_module;
+
     bool operator==(const Recipe&) const = default;
 };
 
@@ -29,6 +39,7 @@ struct OverlayRow {
     std::vector<std::string> targets;
     std::string source;
     std::int64_t verified_at = 0;
+    std::optional<std::string> pkg_config_module;
 };
 
 // RAII wrapper for an open sqlite3 connection used by the overlay database.

src/linkdb/overlay.cpp

@@ -90,6 +90,26 @@ auto overlay_open(const std::filesystem::path& path)
         });
     }
 
+    // Schema migration: legacy overlays predate pkg_config_module.
+    // SQLite ADD COLUMN errors when the column already exists; treat
+    // "duplicate column" as success.
+    constexpr const char* MIGRATE_PC =
+        "ALTER TABLE recipes ADD COLUMN pkg_config_module TEXT";
+    char* mig_err = nullptr;
+    if (sqlite3_exec(state->handle(), MIGRATE_PC, nullptr, nullptr, &mig_err) !=
+        SQLITE_OK) {
+        if (mig_err && std::string_view{mig_err}.find("duplicate column") ==
+                           std::string_view::npos) {
+            std::string msg = std::format("cannot migrate overlay schema: {}",
+                                          mig_err ? mig_err : "?");
+            sqlite3_free(mig_err);
+            return std::unexpected(util::Error{
+                util::ErrorCode::LinkdbCorrupt, std::move(msg), "", path, std::nullopt,
+            });
+        }
+        sqlite3_free(mig_err);
+    }
+
     return state;
 }
 
@@ -99,8 +119,8 @@ auto overlay_insert_manual(OverlayState& state, const std::string& package,
     constexpr const char* SQL =
         "INSERT OR REPLACE INTO recipes "
         "(package, version_range, nixpkgs_attr, find_package, targets, components, source, "
-        " verified_at) "
-        "VALUES (?, ?, ?, ?, ?, NULL, 'manual', ?)";
+        " verified_at, pkg_config_module) "
+        "VALUES (?, ?, ?, ?, ?, NULL, 'manual', ?, ?)";
 
     sqlite3* db = state.handle();
     sqlite3_stmt* stmt = nullptr;
@@ -119,6 +139,11 @@ auto overlay_insert_manual(OverlayState& state, const std::string& package,
     sqlite3_bind_text(stmt, 4, r.find_package.c_str(), -1, SQLITE_TRANSIENT);
     sqlite3_bind_text(stmt, 5, targets_str.c_str(), -1, SQLITE_TRANSIENT);
     sqlite3_bind_int64(stmt, 6, now);
+    if (r.pkg_config_module) {
+        sqlite3_bind_text(stmt, 7, r.pkg_config_module->c_str(), -1, SQLITE_TRANSIENT);
+    } else {
+        sqlite3_bind_null(stmt, 7);
+    }
 
     auto rc = sqlite3_step(stmt);
     sqlite3_finalize(stmt);
@@ -137,8 +162,8 @@ auto overlay_insert(OverlayState& state, const std::string& package,
     constexpr const char* SQL =
         "INSERT OR REPLACE INTO recipes "
         "(package, version_range, nixpkgs_attr, find_package, targets, components, source, "
-        " verified_at) "
-        "VALUES (?, ?, ?, ?, ?, NULL, ?, ?)";
+        " verified_at, pkg_config_module) "
+        "VALUES (?, ?, ?, ?, ?, NULL, ?, ?, ?)";
 
     sqlite3* db = state.handle();
     sqlite3_stmt* stmt = nullptr;
@@ -155,6 +180,11 @@ auto overlay_insert(OverlayState& state, const std::string& package,
     sqlite3_bind_text(stmt, 5, targets_str.c_str(), -1, SQLITE_TRANSIENT);
     sqlite3_bind_text(stmt, 6, source.c_str(), -1, SQLITE_TRANSIENT);
     sqlite3_bind_int64(stmt, 7, verified_at);
+    if (r.pkg_config_module) {
+        sqlite3_bind_text(stmt, 8, r.pkg_config_module->c_str(), -1, SQLITE_TRANSIENT);
+    } else {
+        sqlite3_bind_null(stmt, 8);
+    }
 
     auto rc = sqlite3_step(stmt);
     sqlite3_finalize(stmt);
@@ -245,7 +275,8 @@ auto overlay_evict_auto(OverlayState& state, const std::string& package)
 auto overlay_query(OverlayState& state, const std::string& package)
     -> util::Result<std::vector<OverlayRow>> {
     constexpr const char* SQL =
-        "SELECT version_range, nixpkgs_attr, find_package, targets, source, verified_at "
+        "SELECT version_range, nixpkgs_attr, find_package, targets, source, verified_at, "
+        "       pkg_config_module "
         "FROM recipes WHERE package = ?";
 
     sqlite3* db = state.handle();
@@ -276,6 +307,9 @@ auto overlay_query(OverlayState& state, const std::string& package)
         }
         row.source = column_text(stmt, 4);
         row.verified_at = sqlite3_column_int64(stmt, 5);
+        if (sqlite3_column_type(stmt, 6) != SQLITE_NULL) {
+            row.pkg_config_module = column_text(stmt, 6);
+        }
         out.push_back(std::move(row));
     }
     sqlite3_finalize(stmt);