9 files changed, 262 insertions, 205 deletions

diff --git a/editors/code/package.json b/editors/code/package.json
index 75dbafc05..d8f4287fd 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -238,7 +238,7 @@
                 },
                 "rust-analyzer.cargo.allFeatures": {
                     "type": "boolean",
-                    "default": true,
+                    "default": false,
                     "description": "Activate all available features"
                 },
                 "rust-analyzer.cargo.features": {
@@ -319,7 +319,7 @@
                 },
                 "rust-analyzer.checkOnSave.allFeatures": {
                     "type": "boolean",
-                    "default": true,
+                    "default": false,
                     "markdownDescription": "Check with all features (will be passed as `--all-features`)"
                 },
                 "rust-analyzer.inlayHints.enable": {
diff --git a/editors/code/src/commands.ts b/editors/code/src/commands.ts
index 86302db37..534d2a984 100644
--- a/editors/code/src/commands.ts
+++ b/editors/code/src/commands.ts
@@ -8,6 +8,7 @@ import { spawnSync } from 'child_process';
 import { RunnableQuickPick, selectRunnable, createTask } from './run';
 import { AstInspector } from './ast_inspector';
 import { isRustDocument, sleep, isRustEditor } from './util';
+import { startDebugSession, makeDebugConfig } from './debug';
 
 export * from './ast_inspector';
 export * from './run';
@@ -197,20 +198,6 @@ export function toggleInlayHints(ctx: Ctx): Cmd {
     };
 }
 
-export function run(ctx: Ctx): Cmd {
-    let prevRunnable: RunnableQuickPick | undefined;
-
-    return async () => {
-        const item = await selectRunnable(ctx, prevRunnable);
-        if (!item) return;
-
-        item.detail = 'rerun';
-        prevRunnable = item;
-        const task = createTask(item.runnable);
-        return await vscode.tasks.executeTask(task);
-    };
-}
-
 // Opens the virtual file that will show the syntax tree
 //
 // The contents of the file come from the `TextDocumentContentProvider`
@@ -368,3 +355,62 @@ export function applySnippetWorkspaceEditCommand(_ctx: Ctx): Cmd {
         await applySnippetWorkspaceEdit(edit);
     };
 }
+
+export function run(ctx: Ctx): Cmd {
+    let prevRunnable: RunnableQuickPick | undefined;
+
+    return async () => {
+        const item = await selectRunnable(ctx, prevRunnable);
+        if (!item) return;
+
+        item.detail = 'rerun';
+        prevRunnable = item;
+        const task = createTask(item.runnable);
+        return await vscode.tasks.executeTask(task);
+    };
+}
+
+export function runSingle(ctx: Ctx): Cmd {
+    return async (runnable: ra.Runnable) => {
+        const editor = ctx.activeRustEditor;
+        if (!editor) return;
+
+        const task = createTask(runnable);
+        task.group = vscode.TaskGroup.Build;
+        task.presentationOptions = {
+            reveal: vscode.TaskRevealKind.Always,
+            panel: vscode.TaskPanelKind.Dedicated,
+            clear: true,
+        };
+
+        return vscode.tasks.executeTask(task);
+    };
+}
+
+export function debug(ctx: Ctx): Cmd {
+    let prevDebuggee: RunnableQuickPick | undefined;
+
+    return async () => {
+        const item = await selectRunnable(ctx, prevDebuggee, true);
+        if (!item) return;
+
+        item.detail = 'restart';
+        prevDebuggee = item;
+        return await startDebugSession(ctx, item.runnable);
+    };
+}
+
+export function debugSingle(ctx: Ctx): Cmd {
+    return async (config: ra.Runnable) => {
+        await startDebugSession(ctx, config);
+    };
+}
+
+export function newDebugConfig(ctx: Ctx): Cmd {
+    return async () => {
+        const item = await selectRunnable(ctx, undefined, true, false);
+        if (!item) return;
+
+        await makeDebugConfig(ctx, item.runnable);
+    };
+}
diff --git a/editors/code/src/debug.ts b/editors/code/src/debug.ts
index 027504ecd..a0c9b3ab2 100644
--- a/editors/code/src/debug.ts
+++ b/editors/code/src/debug.ts
@@ -3,46 +3,59 @@ import * as vscode from 'vscode';
 import * as path from 'path';
 import * as ra from './lsp_ext';
 
-import { Cargo } from './cargo';
+import { Cargo } from './toolchain';
 import { Ctx } from "./ctx";
 
 const debugOutput = vscode.window.createOutputChannel("Debug");
 type DebugConfigProvider = (config: ra.Runnable, executable: string, sourceFileMap?: Record<string, string>) => vscode.DebugConfiguration;
 
-function getLldbDebugConfig(config: ra.Runnable, executable: string, sourceFileMap?: Record<string, string>): vscode.DebugConfiguration {
-    return {
-        type: "lldb",
-        request: "launch",
-        name: config.label,
-        program: executable,
-        args: config.extraArgs,
-        cwd: config.cwd,
-        sourceMap: sourceFileMap,
-        sourceLanguages: ["rust"]
-    };
-}
+export async function makeDebugConfig(ctx: Ctx, runnable: ra.Runnable): Promise<void> {
+    const scope = ctx.activeRustEditor?.document.uri;
+    if (!scope) return;
 
-function getCppvsDebugConfig(config: ra.Runnable, executable: string, sourceFileMap?: Record<string, string>): vscode.DebugConfiguration {
-    return {
-        type: (os.platform() === "win32") ? "cppvsdbg" : "cppdbg",
-        request: "launch",
-        name: config.label,
-        program: executable,
-        args: config.extraArgs,
-        cwd: config.cwd,
-        sourceFileMap: sourceFileMap,
-    };
+    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);
 }
 
-async function getDebugExecutable(config: ra.Runnable): Promise<string> {
-    const cargo = new Cargo(config.cwd || '.', debugOutput);
-    const executable = await cargo.executableFromArgs(config.args);
+export async function startDebugSession(ctx: Ctx, runnable: ra.Runnable): Promise<boolean> {
+    let debugConfig: vscode.DebugConfiguration | undefined = undefined;
+    let message = "";
 
-    // if we are here, there were no compilation errors.
-    return executable;
+    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);
 }
 
-export async function getDebugConfiguration(ctx: Ctx, config: ra.Runnable): Promise<vscode.DebugConfiguration | undefined> {
+async function getDebugConfiguration(ctx: Ctx, runnable: ra.Runnable): Promise<vscode.DebugConfiguration | undefined> {
     const editor = ctx.activeRustEditor;
     if (!editor) return;
 
@@ -78,8 +91,8 @@ export async function getDebugConfiguration(ctx: Ctx, config: ra.Runnable): Prom
         return path.normalize(p).replace(wsFolder, '${workspaceRoot}');
     }
 
-    const executable = await getDebugExecutable(config);
-    const debugConfig = knownEngines[debugEngine.id](config, simplifyPath(executable), debugOptions.sourceFileMap);
+    const executable = await getDebugExecutable(runnable);
+    const debugConfig = knownEngines[debugEngine.id](runnable, simplifyPath(executable), debugOptions.sourceFileMap);
     if (debugConfig.type in debugOptions.engineSettings) {
         const settingsMap = (debugOptions.engineSettings as any)[debugConfig.type];
         for (var key in settingsMap) {
@@ -100,25 +113,35 @@ export async function getDebugConfiguration(ctx: Ctx, config: ra.Runnable): Prom
     return debugConfig;
 }
 
-export async function startDebugSession(ctx: Ctx, config: ra.Runnable): Promise<boolean> {
-    let debugConfig: vscode.DebugConfiguration | undefined = undefined;
-    let message = "";
-
-    const wsLaunchSection = vscode.workspace.getConfiguration("launch");
-    const configurations = wsLaunchSection.get<any[]>("configurations") || [];
+async function getDebugExecutable(runnable: ra.Runnable): Promise<string> {
+    const cargo = new Cargo(runnable.args.workspaceRoot || '.', debugOutput);
+    const executable = await cargo.executableFromArgs(runnable.args.cargoArgs);
 
-    const index = configurations.findIndex(c => c.name === config.label);
-    if (-1 !== index) {
-        debugConfig = configurations[index];
-        message = " (from launch.json)";
-        debugOutput.clear();
-    } else {
-        debugConfig = await getDebugConfiguration(ctx, config);
-    }
+    // if we are here, there were no compilation errors.
+    return executable;
+}
 
-    if (!debugConfig) return false;
+function getLldbDebugConfig(runnable: ra.Runnable, executable: 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"]
+    };
+}
 
-    debugOutput.appendLine(`Launching debug configuration${message}:`);
-    debugOutput.appendLine(JSON.stringify(debugConfig, null, 2));
-    return vscode.debug.startDebugging(undefined, debugConfig);
+function getCppvsDebugConfig(runnable: ra.Runnable, executable: 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: sourceFileMap,
+    };
 }
diff --git a/editors/code/src/lsp_ext.ts b/editors/code/src/lsp_ext.ts
index 4da12eb30..c51acfccb 100644
--- a/editors/code/src/lsp_ext.ts
+++ b/editors/code/src/lsp_ext.ts
@@ -45,16 +45,18 @@ export interface RunnablesParams {
     textDocument: lc.TextDocumentIdentifier;
     position: lc.Position | null;
 }
+
 export interface Runnable {
-    range: lc.Range;
     label: string;
-    bin: string;
-    args: string[];
-    extraArgs: string[];
-    env: { [key: string]: string };
-    cwd: string | null;
+    location?: lc.LocationLink;
+    kind: "cargo";
+    args: {
+        workspaceRoot?: string;
+        cargoArgs: string[];
+        executableArgs: string[];
+    };
 }
-export const runnables = new lc.RequestType<RunnablesParams, Runnable[], void>("rust-analyzer/runnables");
+export const runnables = new lc.RequestType<RunnablesParams, Runnable[], void>("experimental/runnables");
 
 export type InlayHint = InlayHint.TypeHint | InlayHint.ParamHint | InlayHint.ChainingHint;
 
diff --git a/editors/code/src/run.ts b/editors/code/src/run.ts
index 8e1ba83ed..5c790741f 100644
--- a/editors/code/src/run.ts
+++ b/editors/code/src/run.ts
@@ -1,9 +1,10 @@
 import * as vscode from 'vscode';
 import * as lc from 'vscode-languageclient';
 import * as ra from './lsp_ext';
+import * as toolchain from "./toolchain";
 
-import { Ctx, Cmd } from './ctx';
-import { startDebugSession, getDebugConfiguration } from './debug';
+import { Ctx } from './ctx';
+import { makeDebugConfig } from './debug';
 
 const quickPickButtons = [{ iconPath: new vscode.ThemeIcon("save"), tooltip: "Save as a launch.json configurtation." }];
 
@@ -64,7 +65,7 @@ export async function selectRunnable(ctx: Ctx, prevRunnable?: RunnableQuickPick,
             quickPick.onDidHide(() => close()),
             quickPick.onDidAccept(() => close(quickPick.selectedItems[0])),
             quickPick.onDidTriggerButton((_button) => {
-                (async () => await makeDebugConfig(ctx, quickPick.activeItems[0]))();
+                (async () => await makeDebugConfig(ctx, quickPick.activeItems[0].runnable))();
                 close();
             }),
             quickPick.onDidChangeActive((active) => {
@@ -83,74 +84,6 @@ export async function selectRunnable(ctx: Ctx, prevRunnable?: RunnableQuickPick,
     });
 }
 
-export function runSingle(ctx: Ctx): Cmd {
-    return async (runnable: ra.Runnable) => {
-        const editor = ctx.activeRustEditor;
-        if (!editor) return;
-
-        const task = createTask(runnable);
-        task.group = vscode.TaskGroup.Build;
-        task.presentationOptions = {
-            reveal: vscode.TaskRevealKind.Always,
-            panel: vscode.TaskPanelKind.Dedicated,
-            clear: true,
-        };
-
-        return vscode.tasks.executeTask(task);
-    };
-}
-
-export function debug(ctx: Ctx): Cmd {
-    let prevDebuggee: RunnableQuickPick | undefined;
-
-    return async () => {
-        const item = await selectRunnable(ctx, prevDebuggee, true);
-        if (!item) return;
-
-        item.detail = 'restart';
-        prevDebuggee = item;
-        return await startDebugSession(ctx, item.runnable);
-    };
-}
-
-export function debugSingle(ctx: Ctx): Cmd {
-    return async (config: ra.Runnable) => {
-        await startDebugSession(ctx, config);
-    };
-}
-
-async function makeDebugConfig(ctx: Ctx, item: RunnableQuickPick): Promise<void> {
-    const scope = ctx.activeRustEditor?.document.uri;
-    if (!scope) return;
-
-    const debugConfig = await getDebugConfiguration(ctx, item.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 function newDebugConfig(ctx: Ctx): Cmd {
-    return async () => {
-        const item = await selectRunnable(ctx, undefined, true, false);
-        if (!item) return;
-
-        await makeDebugConfig(ctx, item);
-    };
-}
-
 export class RunnableQuickPick implements vscode.QuickPickItem {
     public label: string;
     public description?: string | undefined;
@@ -170,18 +103,27 @@ interface CargoTaskDefinition extends vscode.TaskDefinition {
     env?: { [key: string]: string };
 }
 
-export function createTask(spec: ra.Runnable): vscode.Task {
+export function createTask(runnable: ra.Runnable): vscode.Task {
     const TASK_SOURCE = 'Rust';
+
+    let command;
+    switch (runnable.kind) {
+        case "cargo": command = toolchain.getPathForExecutable("cargo");
+    }
+    const args = runnable.args.cargoArgs;
+    if (runnable.args.executableArgs.length > 0) {
+        args.push('--', ...runnable.args.executableArgs);
+    }
     const definition: CargoTaskDefinition = {
         type: 'cargo',
-        label: spec.label,
-        command: spec.bin,
-        args: spec.extraArgs ? [...spec.args, '--', ...spec.extraArgs] : spec.args,
-        env: Object.assign({}, process.env, spec.env),
+        label: runnable.label,
+        command,
+        args,
+        env: Object.assign({}, process.env as { [key: string]: string }, { "RUST_BACKTRACE": "short" }),
     };
 
     const execOption: vscode.ShellExecutionOptions = {
-        cwd: spec.cwd || '.',
+        cwd: runnable.args.workspaceRoot || '.',
         env: definition.env,
     };
     const exec = new vscode.ShellExecution(
diff --git a/editors/code/src/tasks.ts b/editors/code/src/tasks.ts
index 1366c76d6..9748824df 100644
--- a/editors/code/src/tasks.ts
+++ b/editors/code/src/tasks.ts
@@ -1,4 +1,5 @@
 import * as vscode from 'vscode';
+import * as toolchain from "./toolchain";
 
 // This ends up as the `type` key in tasks.json. RLS also uses `cargo` and
 // our configuration should be compatible with it so use the same key.
@@ -24,6 +25,8 @@ class CargoTaskProvider implements vscode.TaskProvider {
         // set of tasks that always exist. These tasks cannot be removed in
         // tasks.json - only tweaked.
 
+        const cargoPath = toolchain.cargoPath();
+
         return [
             { command: 'build', group: vscode.TaskGroup.Build },
             { command: 'check', group: vscode.TaskGroup.Build },
@@ -46,7 +49,7 @@ class CargoTaskProvider implements vscode.TaskProvider {
                     `cargo ${command}`,
                     'rust',
                     // What to do when this command is executed.
-                    new vscode.ShellExecution('cargo', [command]),
+                    new vscode.ShellExecution(cargoPath, [command]),
                     // Problem matchers.
                     ['$rustc'],
                 );
@@ -80,4 +83,4 @@ class CargoTaskProvider implements vscode.TaskProvider {
 export function activateTaskProvider(target: vscode.WorkspaceFolder): vscode.Disposable {
     const provider = new CargoTaskProvider(target);
     return vscode.tasks.registerTaskProvider(TASK_TYPE, provider);
-}
\ No newline at end of file
+}
diff --git a/editors/code/src/cargo.ts b/editors/code/src/toolchain.ts
index a55b2f860..80a7915e9 100644
--- a/editors/code/src/cargo.ts
+++ b/editors/code/src/toolchain.ts
@@ -1,9 +1,10 @@
 import * as cp from 'child_process';
 import * as os from 'os';
 import * as path from 'path';
+import * as fs from 'fs';
 import * as readline from 'readline';
 import { OutputChannel } from 'vscode';
-import { isValidExecutable } from './util';
+import { log, memoize } from './util';
 
 interface CompilationArtifact {
     fileName: string;
@@ -17,33 +18,34 @@ export interface ArtifactSpec {
     filter?: (artifacts: CompilationArtifact[]) => CompilationArtifact[];
 }
 
-export function artifactSpec(args: readonly string[]): ArtifactSpec {
-    const cargoArgs = [...args, "--message-format=json"];
+export class Cargo {
+    constructor(readonly rootFolder: string, readonly output: OutputChannel) { }
 
-    // arguments for a runnable from the quick pick should be updated.
-    // see crates\rust-analyzer\src\main_loop\handlers.rs, handle_code_lens
-    switch (cargoArgs[0]) {
-        case "run": cargoArgs[0] = "build"; break;
-        case "test": {
-            if (!cargoArgs.includes("--no-run")) {
-                cargoArgs.push("--no-run");
+    // Made public for testing purposes
+    static artifactSpec(args: readonly string[]): ArtifactSpec {
+        const cargoArgs = [...args, "--message-format=json"];
+
+        // arguments for a runnable from the quick pick should be updated.
+        // see crates\rust-analyzer\src\main_loop\handlers.rs, handle_code_lens
+        switch (cargoArgs[0]) {
+            case "run": cargoArgs[0] = "build"; break;
+            case "test": {
+                if (!cargoArgs.includes("--no-run")) {
+                    cargoArgs.push("--no-run");
+                }
+                break;
             }
-            break;
         }
-    }
 
-    const result: ArtifactSpec = { cargoArgs: cargoArgs };
-    if (cargoArgs[0] === "test") {
-        // for instance, `crates\rust-analyzer\tests\heavy_tests\main.rs` tests
-        // produce 2 artifacts: {"kind": "bin"} and {"kind": "test"}
-        result.filter = (artifacts) => artifacts.filter(it => it.isTest);
-    }
-
-    return result;
-}
+        const result: ArtifactSpec = { cargoArgs: cargoArgs };
+        if (cargoArgs[0] === "test") {
+            // for instance, `crates\rust-analyzer\tests\heavy_tests\main.rs` tests
+            // produce 2 artifacts: {"kind": "bin"} and {"kind": "test"}
+            result.filter = (artifacts) => artifacts.filter(it => it.isTest);
+        }
 
-export class Cargo {
-    constructor(readonly rootFolder: string, readonly output: OutputChannel) { }
+        return result;
+    }
 
     private async getArtifacts(spec: ArtifactSpec): Promise<CompilationArtifact[]> {
         const artifacts: CompilationArtifact[] = [];
@@ -77,7 +79,7 @@ export class Cargo {
     }
 
     async executableFromArgs(args: readonly string[]): Promise<string> {
-        const artifacts = await this.getArtifacts(artifactSpec(args));
+        const artifacts = await this.getArtifacts(Cargo.artifactSpec(args));
 
         if (artifacts.length === 0) {
             throw new Error('No compilation artifacts');
@@ -94,14 +96,7 @@ export class Cargo {
         onStderrString: (data: string) => void
     ): Promise<number> {
         return new Promise((resolve, reject) => {
-            let cargoPath;
-            try {
-                cargoPath = getCargoPathOrFail();
-            } catch (err) {
-                return reject(err);
-            }
-
-            const cargo = cp.spawn(cargoPath, cargoArgs, {
+            const cargo = cp.spawn(cargoPath(), cargoArgs, {
                 stdio: ['ignore', 'pipe', 'pipe'],
                 cwd: this.rootFolder
             });
@@ -126,26 +121,54 @@ export class Cargo {
     }
 }
 
-// Mirrors `ra_env::get_path_for_executable` implementation
-function getCargoPathOrFail(): string {
-    const envVar = process.env.CARGO;
-    const executableName = "cargo";
+/** Mirrors `ra_toolchain::cargo()` implementation */
+export function cargoPath(): string {
+    return getPathForExecutable("cargo");
+}
+
+/** Mirrors `ra_toolchain::get_path_for_executable()` implementation */
+export const getPathForExecutable = memoize(
+    // We apply caching to decrease file-system interactions
+    (executableName: "cargo" | "rustc" | "rustup"): string => {
+        {
+            const envVar = process.env[executableName.toUpperCase()];
+            if (envVar) return envVar;
+        }
+
+        if (lookupInPath(executableName)) return executableName;
 
-    if (envVar) {
-        if (isValidExecutable(envVar)) return envVar;
+        try {
+            // hmm, `os.homedir()` seems to be infallible
+            // it is not mentioned in docs and cannot be infered by the type signature...
+            const standardPath = path.join(os.homedir(), ".cargo", "bin", executableName);
 
-        throw new Error(`\`${envVar}\` environment variable points to something that's not a valid executable`);
+            if (isFile(standardPath)) return standardPath;
+        } catch (err) {
+            log.error("Failed to read the fs info", err);
+        }
+        return executableName;
     }
+);
 
-    if (isValidExecutable(executableName)) return executableName;
+function lookupInPath(exec: string): boolean {
+    const paths = process.env.PATH ?? "";;
 
-    const standardLocation = path.join(os.homedir(), '.cargo', 'bin', executableName);
+    const candidates = paths.split(path.delimiter).flatMap(dirInPath => {
+        const candidate = path.join(dirInPath, exec);
+        return os.type() === "Windows_NT"
+            ? [candidate, `${candidate}.exe`]
+            : [candidate];
+    });
 
-    if (isValidExecutable(standardLocation)) return standardLocation;
+    return candidates.some(isFile);
+}
 
-    throw new Error(
-        `Failed to find \`${executableName}\` executable. ` +
-        `Make sure \`${executableName}\` is in \`$PATH\`, ` +
-        `or set \`${envVar}\` to point to a valid executable.`
-    );
+function isFile(suspectPath: string): boolean {
+    // It is not mentionned in docs, but `statSync()` throws an error when
+    // the path doesn't exist
+    try {
+        return fs.statSync(suspectPath).isFile();
+    } catch {
+        return false;
+    }
 }
diff --git a/editors/code/src/util.ts b/editors/code/src/util.ts
index 352ef9162..fe3fb71cd 100644
--- a/editors/code/src/util.ts
+++ b/editors/code/src/util.ts
@@ -99,3 +99,21 @@ export function isValidExecutable(path: string): boolean {
 export function setContextValue(key: string, value: any): Thenable<void> {
     return vscode.commands.executeCommand('setContext', key, value);
 }
+
+/**
+ * Returns a higher-order function that caches the results of invoking the
+ * underlying function.
+ */
+export function memoize<Ret, TThis, Param extends string>(func: (this: TThis, arg: Param) => Ret) {
+    const cache = new Map<string, Ret>();
+
+    return function(this: TThis, arg: Param) {
+        const cached = cache.get(arg);
+        if (cached) return cached;
+
+        const result = func.call(this, arg);
+        cache.set(arg, result);
+
+        return result;
+    };
+}
diff --git a/editors/code/tests/unit/launch_config.test.ts b/editors/code/tests/unit/launch_config.test.ts
index d5cf1b74e..68794d53e 100644
--- a/editors/code/tests/unit/launch_config.test.ts
+++ b/editors/code/tests/unit/launch_config.test.ts
@@ -1,25 +1,25 @@
 import * as assert from 'assert';
-import * as cargo from '../../src/cargo';
+import { Cargo } from '../../src/toolchain';
 
 suite('Launch configuration', () => {
 
     suite('Lens', () => {
         test('A binary', async () => {
-            const args = cargo.artifactSpec(["build", "--package", "pkg_name", "--bin", "pkg_name"]);
+            const args = Cargo.artifactSpec(["build", "--package", "pkg_name", "--bin", "pkg_name"]);
 
             assert.deepEqual(args.cargoArgs, ["build", "--package", "pkg_name", "--bin", "pkg_name", "--message-format=json"]);
             assert.deepEqual(args.filter, undefined);
         });
 
         test('One of Multiple Binaries', async () => {
-            const args = cargo.artifactSpec(["build", "--package", "pkg_name", "--bin", "bin1"]);
+            const args = Cargo.artifactSpec(["build", "--package", "pkg_name", "--bin", "bin1"]);
 
             assert.deepEqual(args.cargoArgs, ["build", "--package", "pkg_name", "--bin", "bin1", "--message-format=json"]);
             assert.deepEqual(args.filter, undefined);
         });
 
         test('A test', async () => {
-            const args = cargo.artifactSpec(["test", "--package", "pkg_name", "--lib", "--no-run"]);
+            const args = Cargo.artifactSpec(["test", "--package", "pkg_name", "--lib", "--no-run"]);
 
             assert.deepEqual(args.cargoArgs, ["test", "--package", "pkg_name", "--lib", "--no-run", "--message-format=json"]);
             assert.notDeepEqual(args.filter, undefined);
@@ -28,7 +28,7 @@ suite('Launch configuration', () => {
 
     suite('QuickPick', () => {
         test('A binary', async () => {
-            const args = cargo.artifactSpec(["run", "--package", "pkg_name", "--bin", "pkg_name"]);
+            const args = Cargo.artifactSpec(["run", "--package", "pkg_name", "--bin", "pkg_name"]);
 
             assert.deepEqual(args.cargoArgs, ["build", "--package", "pkg_name", "--bin", "pkg_name", "--message-format=json"]);
             assert.deepEqual(args.filter, undefined);
@@ -36,14 +36,14 @@ suite('Launch configuration', () => {
 
 
         test('One of Multiple Binaries', async () => {
-            const args = cargo.artifactSpec(["run", "--package", "pkg_name", "--bin", "bin2"]);
+            const args = Cargo.artifactSpec(["run", "--package", "pkg_name", "--bin", "bin2"]);
 
             assert.deepEqual(args.cargoArgs, ["build", "--package", "pkg_name", "--bin", "bin2", "--message-format=json"]);
             assert.deepEqual(args.filter, undefined);
         });
 
         test('A test', async () => {
-            const args = cargo.artifactSpec(["test", "--package", "pkg_name", "--lib"]);
+            const args = Cargo.artifactSpec(["test", "--package", "pkg_name", "--lib"]);
 
             assert.deepEqual(args.cargoArgs, ["test", "--package", "pkg_name", "--lib", "--message-format=json", "--no-run"]);
             assert.notDeepEqual(args.filter, undefined);