Deprecate non-colocated components.

text/0995-deprecate-non-colocated-components.md

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+---
+stage: accepted
+start-date: 2023-12-15T00:00:00.000Z
+release-date:
+release-versions:
+teams: # delete teams that aren't relevant
+  - cli
+  - framework
+  - learning
+  - typescript
+prs:
+  accepted: https://github.com/emberjs/rfcs/pull/995
+project-link:
+---
+
+<!---
+Directions for above:
+
+stage: Leave as is
+start-date: Fill in with today's date, 2032-12-01T00:00:00.000Z
+release-date: Leave as is
+release-versions: Leave as is
+teams: Include only the [team(s)](README.md#relevant-teams) for which this RFC applies
+prs:
+  accepted: Fill this in with the URL for the Proposal RFC PR
+project-link: Leave as is
+-->
+
+# Deprecate non-co-located components.
+
+## Summary
+
+Deprecates
+- classic component layout
+- pods component layout
+
+
+Once this deprecation is implemented, only the following will be allowed:
+- co-located components 
+- gjs / gts components
+
+## Motivation
+
+These older component layouts force build tooling to keep a lot of resolution rules around, and makes it hard for codemods and other community tooling to effectively work across folks' projects.
+
+
+## Transition Path
+
+There are two types of paths to migrate off the old layouts 
+- use a currently supported multi-file layout (keeping separate `js`, `ts`, and `hbs` files)
+- migrate the component entirely to the latest component format, `gjs`, `gts`, (aka `<template>`)
+
+There are some tools to help with this:
+- [Classic to Colocation](https://github.com/ember-codemods/ember-component-template-colocation-migrator)
+- [Convert pods to Colocation](https://github.com/ijlee2/ember-codemod-pod-to-octane)
+- [Convert to `<template>`](https://github.com/IgnaceMaes/ember-codemod-template-tag)
+
+
+Specifically, these layouts are no longer supported
+
+### Classic 
+
+```
+{app,addon}/
+  components/
+    foo.js
+    namespace/
+      bar.js
+  templates/
+    components/
+      foo.hbs
+      namespace/
+        bar.hbs
+```
+
+### Pods' Component layout.
+
+```
+{app,addon}/
+  components/
+    foo/
+      component.js
+      template.hbs
+    namespace/
+      bar/
+        component.js
+        template.hbs
+```
+
+The above example(s) could fairly easily be migrated (by users) to:
+
+```
+{app,addon}/
+  components/
+    foo.js 
+    foo.hbs
+    namespace/
+      bar.js
+      bar.hbs
+```
+
+Or using `component-structure=nested`
+
+```
+{app,addon}/
+  components/
+    foo/
+      index.js 
+      index.hbs
+    namespace/
+      bar/
+        index.js
+        index.hbs
+```
+
+Note, however, that classic components _importing_ the `layout` and setting it on an `@ember/component` will still work.
+The key thing being deprecated is the runtime resolution of templates, so if there is an import involved, there is no runtime resolution.
+
+### `ember-source`
+
+The blueprint for components will need to remove the `classic` option:
+
+Here is the output at the time of authoring this RFC:
+```bash 
+❯ pnpm ember g component --help
+Requested ember-cli commands:
+
+ember generate <blueprint> <options...>
+  Generates new code from blueprints.
+  aliases: g
+  --dry-run (Boolean) (Default: false)
+    aliases: -d
+  --verbose (Boolean) (Default: false)
+    aliases: -v
+  --pod (Boolean) (Default: false)
+    aliases: -p, -pods
+  --classic (Boolean) (Default: false)
+    aliases: -c
+  --dummy (Boolean) (Default: false)
+    aliases: -dum, -id
+  --in-repo-addon (String) (Default: null)
+    aliases: --in-repo <value>, -ir <value>
+  --lint-fix (Boolean) (Default: true)
+  --in (String) (Default: null) Runs a blueprint against an in repo addon. A path is expected, relative to the root of the project.
+  --typescript (Boolean) Generates a version of the blueprint written in TypeScript (if available).
+    aliases: -ts
+
+      component <name> <options...>
+        Generates a component.
+        --path (String) (Default: components)
+          aliases: --no-path (--path="")
+        --component-class (@ember/component, @glimmer/component, @ember/component/template-only, "") (Default: --no-component-class)
+          aliases: -cc (--component-class=@ember/component), -gc (--component-class=@glimmer/component), -tc (--component-class=@ember/component/template-only), -nc (--component-class=""), --no-component-class (--component-class=""), --with-component-class (--component-class=@glimmer/component)
+        --component-structure (flat, nested, classic) (Default: flat)
+          aliases: -fs (--component-structure=flat), -ns (--component-structure=nested), -cs (--component-structure=classic)
+
+```
+
+Specifically, we'll remove:
+- `--component-structure=classic` and its alias
+
+
+## How We Teach This
+
+Guides and docs already don't mention the above old layouts.
+
+### Deprecation Guide
+
+#### component templates in `templates/components`
+
+**Before**
+```
+{app,addon}
+  components/
+    demo.js
+  templates/
+    components/
+      demo.hbs
+```
+
+**After**
+```
+{app,addon}
+  components/
+    demo.js
+    demo.hbs
+```
+
+**After (gjs)**
+```
+{app,addon}
+  components/
+    demo.gjs
+```
+
+#### Pods
+
+
+**Before**
+```
+{app,addon}
+  components/
+    demo/
+      component.js
+      template.hbs
+```
+
+**After**
+```
+{app,addon}
+  components/
+    demo/
+      index.js
+      index.hbs
+```
+
+**After (non-nested)**
+```
+{app,addon}
+  components/
+    demo.js
+    demo.hbs
+```
+
+**After (gjs)**
+```
+{app,addon}
+  components/
+    demo.gjs
+```
+
+
+## Drawbacks
+
+If upgrading to ember v6 without any changes,
+- Some super old addons may break
+- Some super old apps may break    
+
+In either case, it's been ~4 years since co-located components were introduced, and the deprecation will give folks actionable information for how to move forward (ideally with a link to the deprecation site which can then link to tools folks can try).
+
+## Alternatives
+
+none
+
+## Unresolved questions
+
+none