mirror: remove unused helper functions (#1351)

Summary:
The functions `isSqlSafe` and `_nontransactionallyFindUnusedTableName`
are unused, because we no longer need to dynamically generate SQL, and
all operations are clearly safe by construction.

Test Plan:
That `yarn flow` passes suffices.

wchargin-branch: mirror-prune-helpers

src/graphql/mirror.js

@@ -2081,23 +2081,6 @@ export function _inTransaction<R>(db: Database, fn: () => R): R {
   }
 }
 
-/*
- * In some cases, we need to interpolate user input in SQL queries in
- * positions that do not allow bound variables in prepared statements
- * (e.g., table and column names). In these cases, we manually sanitize.
- *
- * If this function returns `true`, then its argument may be safely
- * included in a SQL identifier. If it returns `false`, then no such
- * guarantee is made (this function is overly conservative, so it is
- * possible that the argument may in fact be safe).
- *
- * For instance, the function will return `true` if passed "col", but
- * will return `false` if passed "'); DROP TABLE objects; --".
- */
-function isSqlSafe(token: string) {
-  return !token.match(/[^A-Za-z0-9_]/);
-}
-
 /**
  * Convert a prepared statement into a JS function that executes that
  * statement and asserts that it makes exactly one change to the
@@ -2148,48 +2131,3 @@ export function _makeSingleUpdateFunction<Args: BindingDictionary>(
     }
   };
 }
-
-/**
- * Find a name for a new table (or index) that starts with the given
- * prefix and is not used by any current table or index.
- *
- * This function does not actually create any tables. Consider including
- * it in a transaction that subsequently creates the table.
- *
- * The provided prefix must be a SQL-safe string, or an error will be
- * thrown.
- *
- * The result will be a SQL-safe string, and will not need to be quoted
- * unless the provided prefix does.
- *
- * See: `isSqlSafe`.
- */
-export function _nontransactionallyFindUnusedTableName(
-  db: Database,
-  prefix: string
-) {
-  if (!isSqlSafe(prefix)) {
-    throw new Error("Unsafe table name prefix: " + JSON.stringify(prefix));
-  }
-  const result: string = db
-    .prepare(
-      dedent`\
-        SELECT :prefix || (IFNULL(MAX(CAST(suffix AS INTEGER)), 0) + 1)
-        FROM (
-            SELECT SUBSTR(name, LENGTH(:prefix) + 1) AS suffix
-            FROM sqlite_master
-            WHERE SUBSTR(name, 1, LENGTH(:prefix)) = :prefix
-        )
-      `
-    )
-    .pluck()
-    .get({prefix});
-  // istanbul ignore if: should not be possible---it only has the
-  // prefix (which is safe as defined above) and a trailing integer.
-  if (!isSqlSafe(result)) {
-    throw new Error(
-      "Invariant violation: unsafe table name: " + JSON.stringify(result)
-    );
-  }
-  return result;
-}

src/graphql/mirror.test.js

@@ -12,7 +12,6 @@ import {
   _buildSchemaInfo,
   _inTransaction,
   _makeSingleUpdateFunction,
-  _nontransactionallyFindUnusedTableName,
   Mirror,
 } from "./mirror";
 
@@ -3692,73 +3691,4 @@ describe("graphql/mirror", () => {
       );
     });
   });
-
-  describe("_nontransactionallyFindUnusedTableName", () => {
-    it("throws if the name is not SQL-safe", () => {
-      const db = new Database(":memory:");
-      expect(() => {
-        _nontransactionallyFindUnusedTableName(db, "w a t");
-      }).toThrow('Unsafe table name prefix: "w a t"');
-    });
-    it("does not actually create any tables or indices", () => {
-      const db = new Database(":memory:");
-      db.prepare("CREATE TABLE tab (col)").run();
-      db.prepare("CREATE INDEX idx ON tab (col)").run();
-      const getMaster = db.prepare(
-        dedent`
-          SELECT
-              type, name, tbl_name, rootpage, sql
-          FROM sqlite_master
-          ORDER BY
-              type, name, tbl_name, rootpage, sql
-        `
-      );
-      const pre = getMaster.all();
-      expect(pre).toHaveLength(2); // one table, one index
-      _nontransactionallyFindUnusedTableName(db, "hello");
-      const post = getMaster.all();
-      expect(post).toEqual(pre);
-    });
-    it("behaves when there are no conflicts", () => {
-      const db = new Database(":memory:");
-      db.prepare("CREATE TABLE three (col)").run();
-      expect(_nontransactionallyFindUnusedTableName(db, "two_")).toEqual(
-        "two_1"
-      );
-    });
-    it("behaves when there are table-name conflicts", () => {
-      const db = new Database(":memory:");
-      db.prepare("CREATE TABLE two_1 (col)").run();
-      expect(_nontransactionallyFindUnusedTableName(db, "two_")).toEqual(
-        "two_2"
-      );
-    });
-    it("behaves when there are index-name conflicts", () => {
-      const db = new Database(":memory:");
-      db.prepare("CREATE TABLE tab (col)").run();
-      db.prepare("CREATE INDEX idx_1 ON tab (col)").run();
-      expect(_nontransactionallyFindUnusedTableName(db, "idx_")).toEqual(
-        "idx_2"
-      );
-    });
-    it("behaves when there are discontinuities", () => {
-      const db = new Database(":memory:");
-      db.prepare("CREATE TABLE two_1 (col)").run();
-      db.prepare("CREATE TABLE two_3 (col)").run();
-      expect(_nontransactionallyFindUnusedTableName(db, "two_")).toEqual(
-        // It would also be fine for this to return `two_2`.
-        "two_4"
-      );
-    });
-    it("behaves in the face of lexicographical discontinuities", () => {
-      const db = new Database(":memory:");
-      for (let i = 1; i <= 10; i++) {
-        db.prepare(`CREATE TABLE two_${i} (col)`).run();
-      }
-      expect(_nontransactionallyFindUnusedTableName(db, "two_")).toEqual(
-        "two_11"
-      );
-    });
-    //
-  });
 });