sqlite: open read-only when appropriate

include/revng/Support/SQLite.h

@@ -151,20 +151,32 @@ private:
   CUniquePtr<sqlite3_close_v2, SQLITE_OK> Connection;
 
 public:
-  Database(llvm::StringRef Path) {
+  enum class OpenMode {
+    ReadWrite,
+    ReadOnly
+  };
+
+  Database(llvm::StringRef Path, OpenMode Mode) {
     sqlite3 *Ptr = nullptr;
     int Result;
 
-    if (Path == ":memory:")
+    if (Path == ":memory:") {
       Result = sqlite3_open_v2("",
                                &Ptr,
                                SQLITE_OPEN_MEMORY | SQLITE_OPEN_PRIVATECACHE,
                                NULL);
-    else
+    } else if (Mode == OpenMode::ReadOnly) {
+      std::string URI = ("file:" + Path.str() + "?immutable=1");
+      Result = sqlite3_open_v2(URI.c_str(),
+                               &Ptr,
+                               SQLITE_OPEN_READONLY | SQLITE_OPEN_URI,
+                               NULL);
+    } else {
       Result = sqlite3_open_v2(Path.str().c_str(),
                                &Ptr,
                                SQLITE_OPEN_READWRITE,
                                NULL);
+    }
     revng_assert(Result == SQLITE_OK);
 
     Connection.reset(Ptr);

lib/Model/Importer/ImportPrototypesFromDatabase.cpp

@@ -84,7 +84,8 @@ private:
   sqlite::Database Database;
 
 public:
-  PrototypeDatabase(llvm::StringRef Path) : Database(Path) {}
+  PrototypeDatabase(llvm::StringRef Path) :
+    Database(Path, sqlite::Database::OpenMode::ReadOnly) {}
 
   /// Find a platform by its exact name.
   /// Returns -1 if no platform with that name exists.

share/revng/test/configuration/revng-db/db-invariants.yml

@@ -17,5 +17,5 @@ commands:
       - type: source
         filter: db-invariants
     command: |-
-      sqlite3 "$SOURCES_ROOT/share/revng/prototypes.sqlite" < "$INPUT"
+      sqlite3 -cmd ".open \"file:$SOURCES_ROOT/share/revng/prototypes.sqlite?immutable=1\"" < "$INPUT"
         | FileCheck "$INPUT"