`import './file.json'`: This module is declared with using 'export ='

In short, JSON files's implied type definition is always defined via export =, even if I'm using module: es2015, causing it to error unless I use an unnecessary flag (allowSyntheticDefaultImports)

TypeScript Version: 3.9.0-dev.20200326

Search Terms:

import require json module commonjs es2015

Code

import list from "./list.json";

for (const item of list) {
	console.log(item)
}

{
	"compilerOptions": {
		"outDir": "distribution",
		"target": "es2017",
		"module": "es2015",
		"moduleResolution": "node",
		"resolveJsonModule": true,
		"strict": true
	},
	"files": [
		"index.ts"
	]
}

Expected behavior:

list is of type string[]

Actual behavior:

index.ts:1:8 - error TS1259: Module '"./list"' can only be default-imported using the 'allowSyntheticDefaultImports' flag

1 import list from "./list.json";
         ~~~~

  list.json:1:1
    1 [
      ~
    This module is declared with using 'export =', and can only be used with a default import when using the 'allowSyntheticDefaultImports' flag.


Found 1 error.

Workaround:

1. allowSyntheticDefaultImports: true works as expected, but that flag is unsafe and I don't want (need) to use it.

2. declare module './list.json' {
   	const list: string[];
   	export default list;
   }
   

Playground Link: repro.zip

Related Issues: https://github.com/microsoft/TypeScript/issues/15146

issue にリンクされている repro.zip から始め、特に index.ts、list.json、および resolveJsonModule と module: es2015 の tsconfig 設定を確認してください。関連する issue #15146 と動作を比較してください。完了条件は、allowSyntheticDefaultImports なしで示されている default import の型チェックが通り、list が string[] として推論されることです。