feature: Add editor for .class, .semanticdb and tasty files

[tgodzik]

This allows users to use metals decoding for binary files. It will show up after "open anyway" and we can make Metals the default in the settings.

Summary by CodeRabbit

• New Features
  • Open decompiled class files (.class, .tasty, .semanticdb) in a readable custom editor instead of being treated as binary, making decoded output viewable inline.
  • Added a new window-scoped setting to control class-file decoding behavior (default uses a decompiler, with options like cfr, javap, javap-verbose, or disable), so you can choose how class files are displayed.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 4e821d50-5cdf-4366-94b0-af22f32283a5

📥 Commits

Reviewing files that changed from the base of the PR and between 20d0401 and b06fd31.

📒 Files selected for processing (3)

• package.json
• src/classFileCustomEditor.ts
• src/extension.ts

🚧 Files skipped from review as they are similar to previous changes (2)

• src/extension.ts
• src/classFileCustomEditor.ts

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📝 Walkthrough

Walkthrough

Adds a VS Code custom readonly editor (viewType "metals.classDecoder") to decode and display .class, .tasty, and .semanticdb files; introduces a window-scoped metals.classFileOpenEncoding setting (default "cfr") to control decode mode or disable decoding.

Changes

Cohort / File(s)	Summary
Configuration & Custom Editor Registration package.json	Added contributes.customEditors entry for metals.classDecoder targeting *.class, *.tasty, *.semanticdb. Added window-scoped metals.classFileOpenEncoding (string, default "cfr", enum ["none","cfr","javap","javap-verbose"]).
Custom Editor Implementation src/classFileCustomEditor.ts	New exported METALS_CLASS_FILE_CUSTOM_EDITOR_VIEW_TYPE constant and registerMetalsClassFileCustomEditor. Implements a CustomReadonlyEditorProvider that ensures the LanguageClient is running, selects decode mode (suffix-based or config), calls decodeAndShowFile for supported modes, and falls back to opening raw text with error handling.
Extension Integration src/extension.ts	Imports and registers the Metals class-file custom editor during launchMetals after content providers and before command registration.

Sequence Diagram

sequenceDiagram
    participant User
    participant VSCode as VS Code
    participant CustomEditor as Custom Editor Provider
    participant LanguageClient
    participant MetalsServer as Metals Server
    participant FileDecoder as decodeAndShowFile

    User->>VSCode: Open `.class`/`.tasty`/`.semanticdb` file
    VSCode->>CustomEditor: Resolve custom editor (metals.classDecoder)
    CustomEditor->>LanguageClient: Ensure client started
    LanguageClient-->>CustomEditor: Client ready
    CustomEditor->>CustomEditor: Determine decode mode (file suffix or `metals.classFileOpenEncoding`)
    alt Mode is "none" or unsupported
        CustomEditor->>VSCode: Open file as text editor
    else Mode is supported
        CustomEditor->>FileDecoder: Request decoded content with mode
        FileDecoder->>MetalsServer: Ask for decoded output
        MetalsServer-->>FileDecoder: Return decoded content
        FileDecoder->>VSCode: Render decoded content in webview
    end
    VSCode-->>User: Display file content

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

🐇 I nibble bytes and hop with glee,
I peel back class files for you to see,
CFR or javap, tasty treats unfold,
Semantic whispers quietly told,
Hooray—decoded daisies in my code-filled tree!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: adding a custom editor for binary file types (.class, .semanticdb, and .tasty files), which aligns with the core functionality implemented across the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/classFileCustomEditor.ts (1)

79-81: Simplify redundant mode check.

mode !== "tasty-decoded" is unnecessary here because "tasty-decoded" is already allowed by isClassFileOpenDecoder(mode).

Suggested cleanup

-          if (
-            mode === "none" ||
-            (!isClassFileOpenDecoder(mode) && mode !== "tasty-decoded")
-          ) {
+          if (mode === "none" || !isClassFileOpenDecoder(mode)) {

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/classFileCustomEditor.ts` around lines 79 - 81, The condition block in
the class file editor contains a redundant check: remove the explicit `mode !==
"tasty-decoded"` from the compound conditional and rely on
`isClassFileOpenDecoder(mode)` to already allow `"tasty-decoded"`; update the
conditional around `mode === "none" || (!isClassFileOpenDecoder(mode) && mode
!== "tasty-decoded")` to the simplified form using only `mode === "none" ||
!isClassFileOpenDecoder(mode)` so the logic stays equivalent and clearer (locate
the check near the existing `isClassFileOpenDecoder(mode)` usage in
classFileCustomEditor.ts).

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@src/classFileCustomEditor.ts`:
- Line 68: Replace the use of the var declaration for the variable named "mode"
with a block-scoped let declaration to satisfy the ESLint no-var rule; locate
the var mode declaration in src/classFileCustomEditor.ts (identifier: mode) and
change it to let mode so CI linting passes and scoping is correct.

---

Nitpick comments:
In `@src/classFileCustomEditor.ts`:
- Around line 79-81: The condition block in the class file editor contains a
redundant check: remove the explicit `mode !== "tasty-decoded"` from the
compound conditional and rely on `isClassFileOpenDecoder(mode)` to already allow
`"tasty-decoded"`; update the conditional around `mode === "none" ||
(!isClassFileOpenDecoder(mode) && mode !== "tasty-decoded")` to the simplified
form using only `mode === "none" || !isClassFileOpenDecoder(mode)` so the logic
stays equivalent and clearer (locate the check near the existing
`isClassFileOpenDecoder(mode)` usage in classFileCustomEditor.ts).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ffd54823-fadc-4d91-83d0-b59c12e546ad

📥 Commits

Reviewing files that changed from the base of the PR and between 8d61f27 and 20d0401.

📒 Files selected for processing (3)

• package.json
• src/classFileCustomEditor.ts
• src/extension.ts