Chapter 2: Legacy Architecture and Feature Model

Welcome to Chapter 2: Legacy Architecture and Feature Model. In this part of OpenCode AI Legacy Tutorial: Archived Terminal Agent Workflows and Migration to Crush, you will build an intuitive mental model first, then move into concrete implementation details and practical production tradeoffs.

This chapter reviews the core product model to preserve useful patterns.

Learning Goals

• understand TUI-first terminal architecture
• map session/tool/model capabilities
• identify still-useful interaction patterns
• distinguish reusable ideas from legacy constraints

Architecture Highlights

• Bubble Tea-based interactive terminal UX
• multi-provider model support with configurable agents
• local session persistence and context compaction features

Source References

• OpenCode AI README
• OpenCode AI Source Tree

Summary

You now understand what parts of the legacy architecture remain worth carrying forward.

Next: Chapter 3: Installation and Configuration Baseline

Source Code Walkthrough

internal/lsp/methods.go

The References function in internal/lsp/methods.go handles a key part of this chapter's functionality:

}

// References sends a textDocument/references request to the LSP server.
// A request to resolve project-wide references for the symbol denoted by the given text document position. The request's parameter is of type ReferenceParams the response is of type Location Location[] or a Thenable that resolves to such.
func (c *Client) References(ctx context.Context, params protocol.ReferenceParams) ([]protocol.Location, error) {
	var result []protocol.Location
	err := c.Call(ctx, "textDocument/references", params, &result)
	return result, err
}

// DocumentHighlight sends a textDocument/documentHighlight request to the LSP server.
// Request to resolve a DocumentHighlight for a given text document position. The request's parameter is of type TextDocumentPosition the request response is an array of type DocumentHighlight or a Thenable that resolves to such.
func (c *Client) DocumentHighlight(ctx context.Context, params protocol.DocumentHighlightParams) ([]protocol.DocumentHighlight, error) {
	var result []protocol.DocumentHighlight
	err := c.Call(ctx, "textDocument/documentHighlight", params, &result)
	return result, err
}

// DocumentSymbol sends a textDocument/documentSymbol request to the LSP server.
// A request to list all symbols found in a given text document. The request's parameter is of type TextDocumentIdentifier the response is of type SymbolInformation SymbolInformation[] or a Thenable that resolves to such.
func (c *Client) DocumentSymbol(ctx context.Context, params protocol.DocumentSymbolParams) (protocol.Or_Result_textDocument_documentSymbol, error) {
	var result protocol.Or_Result_textDocument_documentSymbol
	err := c.Call(ctx, "textDocument/documentSymbol", params, &result)
	return result, err
}

// CodeAction sends a textDocument/codeAction request to the LSP server.
// A request to provide commands for the given text document and range.
func (c *Client) CodeAction(ctx context.Context, params protocol.CodeActionParams) ([]protocol.Or_Result_textDocument_codeAction_Item0_Elem, error) {
	var result []protocol.Or_Result_textDocument_codeAction_Item0_Elem
	err := c.Call(ctx, "textDocument/codeAction", params, &result)
	return result, err

This function is important because it defines how OpenCode AI Legacy Tutorial: Archived Terminal Agent Workflows and Migration to Crush implements the patterns covered in this chapter.

internal/lsp/methods.go

The DocumentHighlight function in internal/lsp/methods.go handles a key part of this chapter's functionality:

}

// DocumentHighlight sends a textDocument/documentHighlight request to the LSP server.
// Request to resolve a DocumentHighlight for a given text document position. The request's parameter is of type TextDocumentPosition the request response is an array of type DocumentHighlight or a Thenable that resolves to such.
func (c *Client) DocumentHighlight(ctx context.Context, params protocol.DocumentHighlightParams) ([]protocol.DocumentHighlight, error) {
	var result []protocol.DocumentHighlight
	err := c.Call(ctx, "textDocument/documentHighlight", params, &result)
	return result, err
}

// DocumentSymbol sends a textDocument/documentSymbol request to the LSP server.
// A request to list all symbols found in a given text document. The request's parameter is of type TextDocumentIdentifier the response is of type SymbolInformation SymbolInformation[] or a Thenable that resolves to such.
func (c *Client) DocumentSymbol(ctx context.Context, params protocol.DocumentSymbolParams) (protocol.Or_Result_textDocument_documentSymbol, error) {
	var result protocol.Or_Result_textDocument_documentSymbol
	err := c.Call(ctx, "textDocument/documentSymbol", params, &result)
	return result, err
}

// CodeAction sends a textDocument/codeAction request to the LSP server.
// A request to provide commands for the given text document and range.
func (c *Client) CodeAction(ctx context.Context, params protocol.CodeActionParams) ([]protocol.Or_Result_textDocument_codeAction_Item0_Elem, error) {
	var result []protocol.Or_Result_textDocument_codeAction_Item0_Elem
	err := c.Call(ctx, "textDocument/codeAction", params, &result)
	return result, err
}

// ResolveCodeAction sends a codeAction/resolve request to the LSP server.
// Request to resolve additional information for a given code action.The request's parameter is of type CodeAction the response is of type CodeAction or a Thenable that resolves to such.
func (c *Client) ResolveCodeAction(ctx context.Context, params protocol.CodeAction) (protocol.CodeAction, error) {
	var result protocol.CodeAction
	err := c.Call(ctx, "codeAction/resolve", params, &result)
	return result, err

This function is important because it defines how OpenCode AI Legacy Tutorial: Archived Terminal Agent Workflows and Migration to Crush implements the patterns covered in this chapter.

internal/lsp/methods.go

The DocumentSymbol function in internal/lsp/methods.go handles a key part of this chapter's functionality:

}

// DocumentSymbol sends a textDocument/documentSymbol request to the LSP server.
// A request to list all symbols found in a given text document. The request's parameter is of type TextDocumentIdentifier the response is of type SymbolInformation SymbolInformation[] or a Thenable that resolves to such.
func (c *Client) DocumentSymbol(ctx context.Context, params protocol.DocumentSymbolParams) (protocol.Or_Result_textDocument_documentSymbol, error) {
	var result protocol.Or_Result_textDocument_documentSymbol
	err := c.Call(ctx, "textDocument/documentSymbol", params, &result)
	return result, err
}

// CodeAction sends a textDocument/codeAction request to the LSP server.
// A request to provide commands for the given text document and range.
func (c *Client) CodeAction(ctx context.Context, params protocol.CodeActionParams) ([]protocol.Or_Result_textDocument_codeAction_Item0_Elem, error) {
	var result []protocol.Or_Result_textDocument_codeAction_Item0_Elem
	err := c.Call(ctx, "textDocument/codeAction", params, &result)
	return result, err
}

// ResolveCodeAction sends a codeAction/resolve request to the LSP server.
// Request to resolve additional information for a given code action.The request's parameter is of type CodeAction the response is of type CodeAction or a Thenable that resolves to such.
func (c *Client) ResolveCodeAction(ctx context.Context, params protocol.CodeAction) (protocol.CodeAction, error) {
	var result protocol.CodeAction
	err := c.Call(ctx, "codeAction/resolve", params, &result)
	return result, err
}

// Symbol sends a workspace/symbol request to the LSP server.
// A request to list project-wide symbols matching the query string given by the WorkspaceSymbolParams. The response is of type SymbolInformation SymbolInformation[] or a Thenable that resolves to such. Since 3.17.0 - support for WorkspaceSymbol in the returned data. Clients need to advertise support for WorkspaceSymbols via the client capability workspace.symbol.resolveSupport.
func (c *Client) Symbol(ctx context.Context, params protocol.WorkspaceSymbolParams) (protocol.Or_Result_workspace_symbol, error) {
	var result protocol.Or_Result_workspace_symbol
	err := c.Call(ctx, "workspace/symbol", params, &result)
	return result, err

This function is important because it defines how OpenCode AI Legacy Tutorial: Archived Terminal Agent Workflows and Migration to Crush implements the patterns covered in this chapter.

internal/lsp/methods.go

The CodeAction function in internal/lsp/methods.go handles a key part of this chapter's functionality:

}

// CodeAction sends a textDocument/codeAction request to the LSP server.
// A request to provide commands for the given text document and range.
func (c *Client) CodeAction(ctx context.Context, params protocol.CodeActionParams) ([]protocol.Or_Result_textDocument_codeAction_Item0_Elem, error) {
	var result []protocol.Or_Result_textDocument_codeAction_Item0_Elem
	err := c.Call(ctx, "textDocument/codeAction", params, &result)
	return result, err
}

// ResolveCodeAction sends a codeAction/resolve request to the LSP server.
// Request to resolve additional information for a given code action.The request's parameter is of type CodeAction the response is of type CodeAction or a Thenable that resolves to such.
func (c *Client) ResolveCodeAction(ctx context.Context, params protocol.CodeAction) (protocol.CodeAction, error) {
	var result protocol.CodeAction
	err := c.Call(ctx, "codeAction/resolve", params, &result)
	return result, err
}

// Symbol sends a workspace/symbol request to the LSP server.
// A request to list project-wide symbols matching the query string given by the WorkspaceSymbolParams. The response is of type SymbolInformation SymbolInformation[] or a Thenable that resolves to such. Since 3.17.0 - support for WorkspaceSymbol in the returned data. Clients need to advertise support for WorkspaceSymbols via the client capability workspace.symbol.resolveSupport.
func (c *Client) Symbol(ctx context.Context, params protocol.WorkspaceSymbolParams) (protocol.Or_Result_workspace_symbol, error) {
	var result protocol.Or_Result_workspace_symbol
	err := c.Call(ctx, "workspace/symbol", params, &result)
	return result, err
}

// ResolveWorkspaceSymbol sends a workspaceSymbol/resolve request to the LSP server.
// A request to resolve the range inside the workspace symbol's location. Since 3.17.0
func (c *Client) ResolveWorkspaceSymbol(ctx context.Context, params protocol.WorkspaceSymbol) (protocol.WorkspaceSymbol, error) {
	var result protocol.WorkspaceSymbol
	err := c.Call(ctx, "workspaceSymbol/resolve", params, &result)
	return result, err

This function is important because it defines how OpenCode AI Legacy Tutorial: Archived Terminal Agent Workflows and Migration to Crush implements the patterns covered in this chapter.

How These Components Connect

flowchart TD
    A[References]
    B[DocumentHighlight]
    C[DocumentSymbol]
    D[CodeAction]
    E[ResolveCodeAction]
    A --> B
    B --> C
    C --> D
    D --> E