(core) New type conversion in the backend

Summary: This is https://phab.getgrist.com/D3205 plus some changes (https://github.com/dsagal/grist/compare/type-convert...type-convert-server?expand=1) that move the conversion process to the backend. A new user action ConvertFromColumn uses `call_external` so that the data engine can delegate back to ActiveDoc. Code for creating formatters and parsers is significantly refactored so that most of the logic is in `common` and can be used in different ways.

Test Plan: The original diff adds plenty of tests.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Subscribers: dsagal

Differential Revision: https://phab.getgrist.com/D3240

app/server/lib/ActiveDoc.ts

@@ -41,6 +41,7 @@ import {schema, SCHEMA_VERSION} from 'app/common/schema';
 import {MetaRowRecord} from 'app/common/TableData';
 import {FetchUrlOptions, UploadResult} from 'app/common/uploads';
 import {DocReplacementOptions, DocState, DocStateComparison} from 'app/common/UserAPI';
+import {convertFromColumn} from 'app/common/ValueConverter';
 import {parseUserAction} from 'app/common/ValueParser';
 import {ParseOptions} from 'app/plugin/FileParserAPI';
 import {GristDocAPI} from 'app/plugin/GristAPI';
@@ -1717,6 +1718,12 @@ export class ActiveDoc extends EventEmitter {
       logTimes: true,
       logMeta: {docId: this._docName},
       preferredPythonVersion,
+      sandboxOptions: {
+        exports: {
+          convertFromColumn: (...args: Parameters<ReturnType<typeof convertFromColumn>>) =>
+            convertFromColumn(this.docData!)(...args)
+        }
+      },
     });
   }
 }

app/server/lib/GranularAccess.ts

@@ -87,6 +87,7 @@ const SPECIAL_ACTIONS = new Set(['InitNewDoc',
                                  'TransformAndFinishImport',
                                  'AddView',
                                  'CopyFromColumn',
+                                 'ConvertFromColumn',
                                  'AddHiddenColumn',
                                 ]);
 

app/server/lib/ISandbox.ts

@@ -1,4 +1,5 @@
 import * as log from 'app/server/lib/log';
+import {ISandboxOptions} from 'app/server/lib/NSandbox';
 
 /**
  * Starting to whittle down the options used when creating a sandbox, to leave more
@@ -17,6 +18,8 @@ export interface ISandboxCreationOptions {
   importMount?: string;  // if defined, make this path available read-only as "/importdir"
 
   preferredPythonVersion?: '2' | '3';
+
+  sandboxOptions?: Partial<ISandboxOptions>;
 }
 
 export interface ISandbox {

app/server/lib/NSandbox.ts

@@ -33,7 +33,7 @@ type SandboxMethod = (...args: any[]) => any;
  * started by setting `useGristEntrypoint` (the only exception is
  * in tests) which runs grist/main.py.
  */
-interface ISandboxOptions {
+export interface ISandboxOptions {
   command?: string;       // External program or container to call to run the sandbox.
   args: string[];         // The arguments to pass to the python process.
 
@@ -404,6 +404,7 @@ export class NSandboxCreator implements ISandboxCreator {
       preferredPythonVersion: this._preferredPythonVersion || options.preferredPythonVersion,
       useGristEntrypoint: true,
       importDir: options.importMount,
+      ...options.sandboxOptions,
     };
     return new NSandbox(translatedOptions, spawners[this._flavor]);
   }