Newly created TS plugins cannot install dependencies

[josmas]

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Description

Newly created typescript plugins have "typescript": "^7.0.2" in devDependencies which results in two problems:

1. npm install fails because @blockly/dev-scripts caps TS at ^5
2. even updating dev-scripts, or installing with --legacy-peer-deps, the ts-loader pacakge does not seem to support version 7 yet (TypeError: Cannot read properties of undefined (reading 'fileExists')).

Reproduction steps

1. run npx @blockly/create-package plugin my-plugin --type plugin --typescript
2. see it fail when it tries to install

Priority

There are two issues here, the fact that @blockly-dev-scripts is capping at TS version ^5, and what seems to be a more critical issue which is ts-loader not supporting TS version 7 (I believe the underlying API has changed).

There are two workarounds:

1. Manually modify devDependencies in package.json to TS ^5
2. Manually modify devDependencies in package.json to TS ^6 and install with --legacy-peer-deps

A fix could be added to @blockly/dev-create so that it does not output the latest version of TS available and that would help. Another thing that could help would be updating the version in @blockly/dev-scripts to 6, but this would need some testing. Still, none of those would fix the potential incompatibility with TS 7 (through external dependencies - for what I've seen, the ts-loader package).

I'd be happy to do a bit more digging if you can reproduce and are not already on it. Let me know.

Stack trace

> npx @blockly/create-package plugin my-plugin --type plugin --typescript
fatal: not a git repository (or any of the parent directories): .git
Creating a new Blockly plugin with name my-plugin in /private/tmp/bdiff/my-plugin.

Installing packages. This might take a couple of minutes.
npm error code ERESOLVE
npm error ERESOLVE could not resolve
npm error
npm error While resolving: @blockly/dev-scripts@13.3.0
npm error Found: typescript@7.0.2
npm error node_modules/typescript
npm error   dev typescript@"^7.0.2" from the root project
npm error   peer typescript@">3.6.0" from fork-ts-checker-webpack-plugin@9.1.0
npm error   node_modules/fork-ts-checker-webpack-plugin
npm error     fork-ts-checker-webpack-plugin@"^9.1.0" from @blockly/dev-scripts@13.3.0
npm error     node_modules/@blockly/dev-scripts
npm error       dev @blockly/dev-scripts@"^13.3.0" from the root project
npm error   1 more (ts-loader)
npm error
npm error Could not resolve dependency:
npm error peerOptional typescript@"^4.3.2 || ^5" from @blockly/dev-scripts@13.3.0
npm error node_modules/@blockly/dev-scripts
npm error   dev @blockly/dev-scripts@"^13.3.0" from the root project
npm error
npm error Conflicting peer dependency: typescript@5.9.3
npm error node_modules/typescript
npm error   peerOptional typescript@"^4.3.2 || ^5" from @blockly/dev-scripts@13.3.0
npm error   node_modules/@blockly/dev-scripts
npm error     dev @blockly/dev-scripts@"^13.3.0" from the root project
npm error
npm error Fix the upstream dependency conflict, or retry this command with --force or --legacy-peer-deps to accept an incorrect (and potentially broken) dependency resolution.
npm error
npm error
npm error For a full report see:
npm error //.npm/_logs/2026-09-18T13_52_06_738Z-eresolve-report.txt
npm error A complete log of this run can be found in: //.npm/_logs/2026-09-18T13_52_06_738Z-debug-0.log
node:child_process:1017
    throw err;
    ^

Error: Command failed: cd my-plugin && npm install
    at genericNodeError (node:internal/errors:986:15)
    at wrappedFn (node:internal/errors:540:14)
    at checkExecSyncError (node:child_process:942:11)
    at execSync (node:child_process:1014:15)
    at exports.createPlugin (//.npm/_npx/cff5129890bdc14b/node_modules/@blockly/create-package/bin/plugin.js:193:5)
    at Command.<anonymous> (//.npm/_npx/cff5129890bdc14b/node_modules/@blockly/create-package/bin/create.js:43:5)
    at Command.listener [as _actionHandler] (file:////.npm/_npx/cff5129890bdc14b/node_modules/commander/lib/command.js:569:17)
    at file:////.npm/_npx/cff5129890bdc14b/node_modules/commander/lib/command.js:1616:14
    at Command._chainOrCall (file:////.npm/_npx/cff5129890bdc14b/node_modules/commander/lib/command.js:1500:12)
    at Command._parseCommand (file:////.npm/_npx/cff5129890bdc14b/node_modules/commander/lib/command.js:1615:27) {
  status: 1,
  signal: null,
  output: [ null, null, null ],
  pid: 88987,
  stdout: null,
  stderr: null
}

Screenshots

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Browsers

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