Add Code Actions support (textDocument/codeAction)

[polarmutex]

Feature Request: Code Actions / Quick Fixes (LSP 3.17)

Description

Implement textDocument/codeAction capability to provide context-aware quick fixes and refactorings for common beancount operations.

Use Cases

Quick Fixes (CodeActionKind::QUICKFIX)

Unbalanced Transactions:

• Action: "Balance transaction automatically"
• Calculate missing amount and add balancing posting
• Triggered by diagnostic: "Transaction is not balanced"

Missing Account Declarations:

• Action: "Create account 'Assets:Bank:Checking'"
• Generate open directive with appropriate date
• Triggered by diagnostic: "Account is not open"

Missing Commodity:

• Action: "Declare commodity 'AAPL'"
• Generate commodity directive
• Triggered by diagnostic: "Unknown commodity"

Invalid Account Names:

• Action: "Fix account name capitalization"
• Correct to match existing account
• Suggest similar accounts if typo detected

Refactorings (CodeActionKind::REFACTOR)

Transaction Operations:

• "Add balancing posting" - Insert calculated posting to balance
• "Split transaction" - Convert to multiple transactions
• "Merge postings" - Combine multiple postings to same account
• "Convert currency" - Apply price conversion to posting

Account Operations:

• "Generate balance assertion" - Query balance and insert assertion
• "Add budget entry" - Create budget directive for account
• "Close account" - Generate close directive with appropriate date

Batch Operations:

• "Format all amounts" - Align decimal points
• "Normalize account names" - Fix capitalization across file
• "Add missing tags" - Suggest tags based on payee/account patterns

Implementation Details

File: crates/lsp/src/providers/code_action.rs

Pattern:

pub fn code_actions(
    snapshot: LspServerStateSnapshot,
    params: CodeActionParams,
) -> Result<Option<CodeActionResponse>> {
    let mut actions = vec![];
    
    // Diagnostic-based quick fixes
    for diagnostic in &params.context.diagnostics {
        if diagnostic.message.contains("unbalanced") {
            actions.push(CodeAction {
                title: "Balance transaction automatically".to_string(),
                kind: Some(CodeActionKind::QUICKFIX),
                edit: Some(calculate_balancing_edit(params.range)),
                diagnostics: Some(vec![diagnostic.clone()]),
                ..Default::default()
            });
        }
        
        if diagnostic.message.contains("not open") {
            let account = extract_account_from_diagnostic(diagnostic);
            actions.push(CodeAction {
                title: format!("Create account '{}'", account),
                kind: Some(CodeActionKind::QUICKFIX),
                edit: Some(generate_account_open_edit(&account)),
                diagnostics: Some(vec![diagnostic.clone()]),
                ..Default::default()
            });
        }
    }
    
    // Context-aware refactorings
    let node = get_node_at_position(params.range.start);
    match node.kind() {
        "txn" => {
            if !is_balanced(&node) {
                actions.push(balance_transaction_action());
            }
            actions.push(split_transaction_action());
        }
        "account" => {
            actions.push(generate_balance_assertion_action());
            actions.push(create_budget_entry_action());
        }
        _ => {}
    }
    
    Ok(Some(actions))
}

Capability Registration

Update crates/lsp/src/capabilities.rs:

code_action_provider: Some(CodeActionProviderCapability::Options(
    CodeActionOptions {
        code_action_kinds: Some(vec![
            CodeActionKind::QUICKFIX,
            CodeActionKind::REFACTOR,
        ]),
        resolve_provider: Some(false),
        ..Default::default()
    }
)),

Priority

HIGH - Dramatically improves productivity for common beancount tasks

Implementation Phases

Phase 1: Basic Quick Fixes

• Balance transaction
• Create missing account
• Fix account typos

Phase 2: Advanced Quick Fixes

• Declare missing commodity
• Fix date format
• Correct metadata syntax

Phase 3: Refactorings

• Split/merge transactions
• Generate balance assertions
• Currency conversions
• Batch formatting

Dependencies

• May need to call bean-check or bean-query for balance calculations
• Consider caching account list for faster suggestion matching
• May integrate with existing diagnostic system

References

• LSP 3.17 CodeAction specification
• Existing diagnostics: crates/lsp/src/providers/diagnostics.rs
• Related: Add Hover support (textDocument/hover) #746 (Hover), Add Go to Definition support (textDocument/definition) #747 (Definition), Add Document Symbols support (textDocument/documentSymbol) #748 (Symbols)