(core) Use original column headers during imports

Summary:
When possible, the original column headers from imported
files will now be used as the labels for Grist columns. This includes
values that were previously invalid Grist column identifiers, such
as those containing Unicode.

Test Plan: Updated server and browser tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3261

app/server/lib/ActiveDocImport.ts

@@ -13,7 +13,7 @@ import {BulkColValues, CellValue, fromTableDataAction, TableRecordValue, UserAct
 import * as gutil from 'app/common/gutil';
 import {DocStateComparison} from 'app/common/UserAPI';
 import {ParseFileResult, ParseOptions} from 'app/plugin/FileParserAPI';
-import {GristTable} from 'app/plugin/GristTable';
+import {GristColumn, GristTable} from 'app/plugin/GristTable';
 import {ActiveDoc} from 'app/server/lib/ActiveDoc';
 import {DocSession, OptDocSession} from 'app/server/lib/DocSession';
 import * as log from 'app/server/lib/log';
@@ -294,8 +294,9 @@ export class ActiveDocImport {
       const origTableName = table.table_name ? table.table_name : '';
       const transformRule = transformRuleMap && transformRuleMap.hasOwnProperty(origTableName) ?
         transformRuleMap[origTableName] : null;
+      const columnMetadata = addLabelsIfPossible(table.column_metadata);
       const result: ApplyUAResult = await this._activeDoc.applyUserActions(docSession,
-        [["AddTable", hiddenTableName, table.column_metadata]]);
+        [["AddTable", hiddenTableName, columnMetadata]]);
       const retValue: AddTableRetValue = result.retValues[0];
       const hiddenTableId = retValue.table_id;    // The sanitized version of the table name.
       const hiddenTableColIds = retValue.columns;      // The sanitized names of the columns.
@@ -727,3 +728,12 @@ function getMergeFunction({type}: MergeStrategy): MergeFunction {
     }
   }
 }
+
+/**
+ * If `columns` is populated with non-blank column ids, adds labels to all
+ * columns using the values set for the column ids. Otherwise, returns
+ * a copy of columns with no modifications made.
+ */
+function addLabelsIfPossible(columns: GristColumn[]) {
+  return columns.map(c => (c.id ? {...c, label: c.id} : c));
+}

sandbox/grist/import_actions.py

@@ -156,8 +156,9 @@ class ImportActions(object):
       isCopyFormula = (formula.startswith("$") and formula[1:] in src_cols)
 
       if gen_all or not isCopyFormula:
-        #if colId specified, use that. Else label is fine
-        new_col_id = _import_transform_col_prefix + (c.colId or c.label)
+        # If colId specified, use that. Otherwise, use the (sanitized) label.
+        col_id = c.colId or identifiers.pick_col_ident(c.label)
+        new_col_id = _import_transform_col_prefix + col_id
         new_col_spec = {
           "label": c.label,
           "type": c.type,