libstore: add SQLite::Settings struct for explicit configuration

Progress on #5638

Replace the SQLite constructor's mode parameter with a Settings struct
that includes both the open mode and useWAL flag. This makes the
dependency on useSQLiteWAL explicit at call sites rather than having
it read from the global settings inside the constructor.

All call sites now explicitly pass settings.useSQLiteWAL, preparing
for downstream work where stores can pass their own settings instead
of relying on the global.

src/libexpr/eval-cache.cc

@@ -75,7 +75,7 @@ struct AttrDb
 
         auto dbPath = cacheDir / (fingerprint.to_string(HashFormat::Base16, false) + ".sqlite");
 
-        state->db = SQLite(dbPath);
+        state->db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
         state->db.isCache();
         state->db.exec(schema);
 

src/libfetchers/cache.cc

@@ -41,7 +41,7 @@ struct CacheImpl : Cache
         auto dbPath = (getCacheDir() / "fetcher-cache-v4.sqlite").string();
         createDirs(dirOf(dbPath));
 
-        state->db = SQLite(dbPath);
+        state->db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
         state->db.isCache();
         state->db.exec(schema);
 

src/libstore-tests/nar-info-disk-cache.cc

@@ -2,6 +2,7 @@
 
 #include <gtest/gtest.h>
 #include <rapidcheck/gtest.h>
+#include "nix/store/globals.hh"
 #include "nix/store/sqlite.hh"
 #include <sqlite3.h>
 
@@ -48,7 +49,7 @@ TEST(NarInfoDiskCacheImpl, create_and_read)
 
         // We're going to pay special attention to the id field because we had a bug
         // that changed it.
-        db = SQLite(dbPath);
+        db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
         getIds.create(db, "select id from BinaryCaches where url = 'http://foo'");
 
         {

src/libstore/include/nix/store/sqlite.hh

@@ -42,7 +42,13 @@ struct SQLite
 
     SQLite() {}
 
-    SQLite(const std::filesystem::path & path, SQLiteOpenMode mode = SQLiteOpenMode::Normal);
+    struct Settings
+    {
+        SQLiteOpenMode mode = SQLiteOpenMode::Normal;
+        bool useWAL;
+    };
+
+    SQLite(const std::filesystem::path & path, Settings && settings);
     SQLite(const SQLite & from) = delete;
     SQLite & operator=(const SQLite & from) = delete;
 

src/libstore/local-store.cc

@@ -481,7 +481,7 @@ void LocalStore::openDB(State & state, bool create)
     auto openMode = config->readOnly ? SQLiteOpenMode::Immutable
                     : create         ? SQLiteOpenMode::Normal
                                      : SQLiteOpenMode::NoCreate;
-    state.db = SQLite(std::filesystem::path(dbDir) / "db.sqlite", openMode);
+    state.db = SQLite(std::filesystem::path(dbDir) / "db.sqlite", {.mode = openMode, .useWAL = settings.useSQLiteWAL});
 
 #ifdef __CYGWIN__
     /* The cygwin version of sqlite3 has a patch which calls

src/libstore/nar-info-disk-cache.cc

@@ -92,7 +92,7 @@ public:
 
         createDirs(dirOf(dbPath));
 
-        state->db = SQLite(dbPath);
+        state->db = SQLite(dbPath, {.useWAL = settings.useSQLiteWAL});
 
         state->db.isCache();
 

src/libstore/sqlite.cc

@@ -62,7 +62,7 @@ static void traceSQL(void * x, const char * sql)
     notice("SQL<[%1%]>", sql);
 };
 
-SQLite::SQLite(const std::filesystem::path & path, SQLiteOpenMode mode)
+SQLite::SQLite(const std::filesystem::path & path, Settings && settings)
 {
     // Work around a ZFS issue where SQLite's truncate() call on
     // db.sqlite-shm can randomly take up to a few seconds. See
@@ -89,10 +89,10 @@ SQLite::SQLite(const std::filesystem::path & path, SQLiteOpenMode mode)
     // useSQLiteWAL also indicates what virtual file system we need.  Using
     // `unix-dotfile` is needed on NFS file systems and on Windows' Subsystem
     // for Linux (WSL) where useSQLiteWAL should be false by default.
-    const char * vfs = settings.useSQLiteWAL ? 0 : "unix-dotfile";
-    bool immutable = mode == SQLiteOpenMode::Immutable;
+    const char * vfs = settings.useWAL ? 0 : "unix-dotfile";
+    bool immutable = settings.mode == SQLiteOpenMode::Immutable;
     int flags = immutable ? SQLITE_OPEN_READONLY : SQLITE_OPEN_READWRITE;
-    if (mode == SQLiteOpenMode::Normal)
+    if (settings.mode == SQLiteOpenMode::Normal)
         flags |= SQLITE_OPEN_CREATE;
     auto uri = "file:" + percentEncode(path.string()) + "?immutable=" + (immutable ? "1" : "0");
     int ret = sqlite3_open_v2(uri.c_str(), &db, SQLITE_OPEN_URI | flags, vfs);