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docs: idiot blog post
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Jan De Dobbeleer
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docs/blog/2022-03-28-idiots-everywhere.md
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docs/blog/2022-03-28-idiots-everywhere.md
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---
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title: "What idiot wrote this code?"
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description: "It was me..."
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slug: idiots-everywhere
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authors:
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- name: Jan De Dobbeleer
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title: Maintainer
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url: https://github.com/jandedobbeleer
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image_url: https://avatars.githubusercontent.com/u/2492783?v=4
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tags: [weekly, ohmyposh]
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hide_table_of_contents: false
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---
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It finally happened, **I introduced a bug** that only appears in 1 use case and it can’t be resolved as it’s the result of
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using an old and new version of Oh My posh at the same time. Who does that you might ask? Well, it can be because you’re
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using WSL on Windows, or VM’s on any system while sharing the same configuration cross installation.
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Not the main use-case, but also not exotic either.
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## What happened?
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In the beginning of the year, after what has been quite the struggle, I was finally able to deliver **the most important
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architectural update** since the introduction of the rewrite in Go. Because of this, a migration of old configs was needed
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so that no end user would have to go through the ordeal of figuring out what to map where, it's a very logical process
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and obviously computers are better at that.
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To facilitate this, I added a config property called `version` which can be incremented when the configuration evolves
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and triggers an automatic migration when necessary. The logic to identify the need for migration is as follows:
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```go
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if !env.Flags().Migrate && cfg.Version != configVersion {
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cfg.BackupAndMigrate(env)
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}
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```
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If you're observant, you might already spot the issue now that you know the use-case. For those of us who like to read
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and not think, the result is rather straightforward as it will always run the migration, either when forced (because you
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can use `oh-my-posh config migrate` manually), or when the current config version doesn't match the required config
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version. _Simple, right?_ And this works according to expectations when updating Oh My Posh. The problem starts when you
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have a shared config, and use multiple versions of Oh My Posh on the same machine.
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Imagine working using multiple shells, one is WSL Ubuntu with a version of Oh My Posh that's still on version 1
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(**S1**). One day, you update PowerShell in Windows to use the latest greatest, using version 2 (**S2**). Starting S2,
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**it automatically migrates the config to version 2**, moving the `template` property to the segment's model.
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In practice, the following version 1 config:
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```json
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{
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"$schema": "https://raw.githubusercontent.com/JanDeDobbeleer/oh-my-posh/main/themes/schema.json",
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"version": 1,
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"blocks": [
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{
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"type": "prompt",
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"alignment": "left",
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"segments": [
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{
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"background": "#9A348E",
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"foreground": "#ffffff",
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"leading_diamond": "\ue0b6",
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"properties": {
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// highlight-next-line
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"template": "{{ .UserName }} "
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},
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"style": "diamond",
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"type": "session"
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}
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]
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}
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]
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}
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```
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Is migrated to:
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```json
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{
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"$schema": "https://raw.githubusercontent.com/JanDeDobbeleer/oh-my-posh/main/themes/schema.json",
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"version": 2,
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"blocks": [
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{
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"type": "prompt",
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"alignment": "left",
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"segments": [
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{
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"background": "#9A348E",
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"foreground": "#ffffff",
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"leading_diamond": "\ue0b6",
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// highlight-next-line
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"template": "{{ .UserName }} ",
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"style": "diamond",
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"type": "session"
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}
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]
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}
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]
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}
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```
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Awesome, no user interaction at all and _everything works as designed_. However, you now want to do something using S1, and
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due to the logic, Oh My Posh sees that `2 != 1` and **the migration is triggered for version 1**. The migration as such
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is non-breaking, but Oh My Posh doesn't know the `template` property on `segment` in this case. The end result of our
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config above is rather annoying as we're now left with this:
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```json
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{
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"$schema": "https://raw.githubusercontent.com/JanDeDobbeleer/oh-my-posh/main/themes/schema.json",
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"version": 1,
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"blocks": [
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{
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"type": "prompt",
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"alignment": "left",
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"segments": [
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{
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"background": "#9A348E",
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"foreground": "#ffffff",
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"leading_diamond": "\ue0b6",
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"style": "diamond",
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"type": "session"
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}
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]
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}
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]
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}
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```
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😱 the template is gone! Nothing to worry about just yet, Oh My Posh will use the default template so you will still see
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a prompt, and the migration also _creates a backup_ of your previously correct version 2 config. Up to this point you
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can still revert, it's unfortunate, but your local tweaks are still available. If you happen to continue working in S2 at
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this point however, it will once again trigger the migration to version 2 and **overwrite your backup with the faulty
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version 1 config**.
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While the fix for this issue in code is trivial, it's impossible to push that to older versions. People will upgrade
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to the most recent version, and in this specific setup, this is potentially breaking. **The advice is to upgrade all versions
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at once**, so you only migrate once and there's no "old" version of Oh My Posh left to trigger this unwanted side-effect.
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The actual fix for the issue can be found in [7.52.1][fix-version], but due to obvious reasons, it will only work
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going from version 2 to any new config version in the future.
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```go
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if !env.Flags().Migrate && cfg.Version < configVersion {
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cfg.BackupAndMigrate(env)
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}
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```
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While I try hard to come up with every possible edge case when validating this logic, sometimes things slip through.
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Even when looking at this one **I find it challenging not having considered that case**, but it still happened. The
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good news? It won't happen again 😅
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[fix-version]: https://github.com/JanDeDobbeleer/oh-my-posh/releases/tag/v7.52.1
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