code/src/debug.ts

import * as os from "os";
import * as vscode from 'vscode';
import * as path from 'path';
import * as ra from './lsp_ext';

import { Cargo, getRustcId, getSysroot } from './toolchain';
import { Ctx } from "./ctx";
import { prepareEnv } from "./run";

const debugOutput = vscode.window.createOutputChannel("Debug");
type DebugConfigProvider = (config: ra.Runnable, executable: string, env: Record<string, string>, sourceFileMap?: Record<string, string>) => vscode.DebugConfiguration;

export async function makeDebugConfig(ctx: Ctx, runnable: ra.Runnable): Promise<void> {
    const scope = ctx.activeRustEditor?.document.uri;
    if (!scope) return;

    const debugConfig = await getDebugConfiguration(ctx, runnable);
    if (!debugConfig) return;

    const wsLaunchSection = vscode.workspace.getConfiguration("launch", scope);
    const configurations = wsLaunchSection.get<any[]>("configurations") || [];

    const index = configurations.findIndex(c => c.name === debugConfig.name);
    if (index !== -1) {
        const answer = await vscode.window.showErrorMessage(`Launch configuration '${debugConfig.name}' already exists!`, 'Cancel', 'Update');
        if (answer === "Cancel") return;

        configurations[index] = debugConfig;
    } else {
        configurations.push(debugConfig);
    }

    await wsLaunchSection.update("configurations", configurations);
}

export async function startDebugSession(ctx: Ctx, runnable: ra.Runnable): Promise<boolean> {
    let debugConfig: vscode.DebugConfiguration | undefined = undefined;
    let message = "";

    const wsLaunchSection = vscode.workspace.getConfiguration("launch");
    const configurations = wsLaunchSection.get<any[]>("configurations") || [];

    const index = configurations.findIndex(c => c.name === runnable.label);
    if (-1 !== index) {
        debugConfig = configurations[index];
        message = " (from launch.json)";
        debugOutput.clear();
    } else {
        debugConfig = await getDebugConfiguration(ctx, runnable);
    }

    if (!debugConfig) return false;

    debugOutput.appendLine(`Launching debug configuration${message}:`);
    debugOutput.appendLine(JSON.stringify(debugConfig, null, 2));
    return vscode.debug.startDebugging(undefined, debugConfig);
}

async function getDebugConfiguration(ctx: Ctx, runnable: ra.Runnable): Promise<vscode.DebugConfiguration | undefined> {
    const editor = ctx.activeRustEditor;
    if (!editor) return;

    const knownEngines: Record<string, DebugConfigProvider> = {
        "vadimcn.vscode-lldb": getLldbDebugConfig,
        "ms-vscode.cpptools": getCppvsDebugConfig
    };
    const debugOptions = ctx.config.debug;

    let debugEngine = null;
    if (debugOptions.engine === "auto") {
        for (var engineId in knownEngines) {
            debugEngine = vscode.extensions.getExtension(engineId);
            if (debugEngine) break;
        }
    } else {
        debugEngine = vscode.extensions.getExtension(debugOptions.engine);
    }

    if (!debugEngine) {
        await vscode.window.showErrorMessage(`Install [CodeLLDB](https://marketplace.visualstudio.com/items?itemName=vadimcn.vscode-lldb)`
            + ` or [MS C++ tools](https://marketplace.visualstudio.com/items?itemName=ms-vscode.cpptools) extension for debugging.`);
        return;
    }

    debugOutput.clear();
    if (ctx.config.debug.openDebugPane) {
        debugOutput.show(true);
    }
    // folder exists or RA is not active.
    // eslint-disable-next-line @typescript-eslint/no-unnecessary-type-assertion
    const workspaceFolders = vscode.workspace.workspaceFolders!;
    const isMultiFolderWorkspace = workspaceFolders.length > 1;
    const firstWorkspace = workspaceFolders[0];
    const workspace = !isMultiFolderWorkspace || !runnable.args.workspaceRoot ?
        firstWorkspace :
        workspaceFolders.find(w => runnable.args.workspaceRoot?.includes(w.uri.fsPath)) || firstWorkspace;

    const wsFolder = path.normalize(workspace.uri.fsPath);
    const workspaceQualifier = isMultiFolderWorkspace ? `:${workspace.name}` : '';
    function simplifyPath(p: string): string {
        // see https://github.com/rust-analyzer/rust-analyzer/pull/5513#issuecomment-663458818 for why this is needed
        return path.normalize(p).replace(wsFolder, '${workspaceFolder' + workspaceQualifier + '}');
    }

    const executable = await getDebugExecutable(runnable);
    const env = prepareEnv(runnable, ctx.config.runnableEnv);
    let sourceFileMap = debugOptions.sourceFileMap;
    if (sourceFileMap === "auto") {
        // let's try to use the default toolchain
        const commitHash = await getRustcId(wsFolder);
        const sysroot = await getSysroot(wsFolder);
        const rustlib = path.normalize(sysroot + "/lib/rustlib/src/rust");
        sourceFileMap = {};
        sourceFileMap[`/rustc/${commitHash}/`] = rustlib;
    }

    const debugConfig = knownEngines[debugEngine.id](runnable, simplifyPath(executable), env, sourceFileMap);
    if (debugConfig.type in debugOptions.engineSettings) {
        const settingsMap = (debugOptions.engineSettings as any)[debugConfig.type];
        for (var key in settingsMap) {
            debugConfig[key] = settingsMap[key];
        }
    }

    if (debugConfig.name === "run binary") {
        // The LSP side: crates\rust-analyzer\src\main_loop\handlers.rs,
        // fn to_lsp_runnable(...) with RunnableKind::Bin
        debugConfig.name = `run ${path.basename(executable)}`;
    }

    if (debugConfig.cwd) {
        debugConfig.cwd = simplifyPath(debugConfig.cwd);
    }

    return debugConfig;
}

async function getDebugExecutable(runnable: ra.Runnable): Promise<string> {
    const cargo = new Cargo(runnable.args.workspaceRoot || '.', debugOutput);
    const executable = await cargo.executableFromArgs(runnable.args.cargoArgs);

    // if we are here, there were no compilation errors.
    return executable;
}

function getLldbDebugConfig(runnable: ra.Runnable, executable: string, env: Record<string, string>, sourceFileMap?: Record<string, string>): vscode.DebugConfiguration {
    return {
        type: "lldb",
        request: "launch",
        name: runnable.label,
        program: executable,
        args: runnable.args.executableArgs,
        cwd: runnable.args.workspaceRoot,
        sourceMap: sourceFileMap,
        sourceLanguages: ["rust"],
        env
    };
}

function getCppvsDebugConfig(runnable: ra.Runnable, executable: string, env: Record<string, string>, sourceFileMap?: Record<string, string>): vscode.DebugConfiguration {
    return {
        type: (os.platform() === "win32") ? "cppvsdbg" : "cppdbg",
        request: "launch",
        name: runnable.label,
        program: executable,
        args: runnable.args.executableArgs,
        cwd: runnable.args.workspaceRoot,
        sourceFileMap,
        env,
    };
}