Try something really dirty

lib/main.js

@@ -1,10 +1,9 @@
 "use strict";
 var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
-    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
     return new (P || (P = Promise))(function (resolve, reject) {
         function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
         function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
-        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
+        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
         step((generator = generator.apply(thisArg, _arguments || [])).next());
     });
 };

lib/rustup.js

@@ -1,10 +1,9 @@
 "use strict";
 var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
-    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
     return new (P || (P = Promise))(function (resolve, reject) {
         function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
         function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
-        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
+        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
         step((generator = generator.apply(thisArg, _arguments || [])).next());
     });
 };
@@ -22,7 +21,9 @@ const toolCache = __importStar(require("@actions/tool-cache"));
 const path = __importStar(require("path"));
 const os = __importStar(require("os"));
 const fs_1 = require("fs");
+const util_1 = require("util");
 let tempDirectory = process.env['RUNNER_TEMPDIRECTORY'] || '';
+const renameAsync = util_1.promisify(fs_1.rename);
 function install() {
     return __awaiter(this, void 0, void 0, function* () {
         // `rustup` is already installed on Linux and Windows platforms
@@ -36,9 +37,38 @@ function install() {
             // to leverage newer features like "latest latest compatible nightly"
             yield exec.exec('rustup', ['self', 'update']);
             yield exec.exec('rustup', ['set', 'profile', 'minimal']);
+            if (os.platform() == 'win32') {
+                let rustDocsInstalled = false;
+                {
+                    let installedComponents = '';
+                    const options = {
+                        listeners: {
+                            stdout: (data) => {
+                                installedComponents += data.toString();
+                            }
+                        }
+                    };
+                    yield exec.exec('rustup', ['component', 'list'], options);
+                    rustDocsInstalled = installedComponents.match(/rust-docs.+\(installed\)/) != null;
+                }
+                if (rustDocsInstalled) {
+                    let cargoPath = '';
+                    {
+                        const options = {
+                            listeners: {
+                                stdout: (data) => {
+                                    cargoPath += data.toString();
+                                }
+                            }
+                        };
+                        yield exec.exec('where', ['rustup.exe'], options);
+                    }
+                    let rustupPath = cargoPath.split('\\').slice(0, -3).concat([".rustup"]).join("\\");
                     // Github's default Windows install comes with rustup pre-installed with stable, including
                     // rust-docs. This removes the default stable install so that it doesn't update rust-docs.
-            yield exec.exec('rustup', ['toolchain', 'uninstall', 'stable']);
+                    yield renameAsync(`${rustupPath}\\toolchains`, `${rustupPath}\\_toolchains`);
+                }
+            }
         }
     });
 }

package-lock.json

@@ -633,9 +633,9 @@
       "dev": true
     },
     "@types/node": {
-      "version": "12.6.9",
+      "version": "12.12.14",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-12.6.9.tgz",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-12.12.14.tgz",
-      "integrity": "sha512-+YB9FtyxXGyD54p8rXwWaN1EWEyar5L58GlGWgtH2I9rGmLGBQcw63+0jw+ujqVavNuO47S1ByAjm9zdHMnskw==",
+      "integrity": "sha512-u/SJDyXwuihpwjXy7hOOghagLEV1KdAST6syfnOk6QZAMzZuWZqXy5aYYZbh8Jdpd4escVFP0MvftHNDb9pruA==",
       "dev": true
     },
     "@types/semver": {

package.json

@@ -30,7 +30,7 @@
   },
   "devDependencies": {
     "@types/jest": "^24.0.13",
-    "@types/node": "^12.0.4",
+    "@types/node": "^12.12.14",
     "@types/semver": "^6.0.0",
     "jest": "^24.8.0",
     "jest-circus": "^24.7.1",

src/rustup.ts

@@ -3,9 +3,11 @@ import * as exec from '@actions/exec';
 import * as toolCache from '@actions/tool-cache';
 import * as path from 'path';
 import * as os from 'os';
-import {chmodSync} from 'fs';
+import {chmodSync, rename} from 'fs';
+import {promisify} from 'util';
 
 let tempDirectory = process.env['RUNNER_TEMPDIRECTORY'] || '';
+const renameAsync = promisify(rename);
 
 export async function install() {
   // `rustup` is already installed on Linux and Windows platforms
@@ -20,9 +22,40 @@ export async function install() {
     await exec.exec('rustup', ['self', 'update']);
 
     await exec.exec('rustup', ['set', 'profile', 'minimal']);
+
+    if (os.platform() == 'win32') {
+      let rustDocsInstalled = false;
+      {
+        let installedComponents = '';
+        const options = {
+          listeners: {
+            stdout: (data: Buffer) => {
+              installedComponents += data.toString();
+            }
+          }
+        };
+        await exec.exec('rustup', ['component', 'list'], options);
+        rustDocsInstalled = installedComponents.match(/rust-docs.+\(installed\)/) != null;
+      }
+
+      if (rustDocsInstalled) {
+        let cargoPath = '';
+        {
+          const options = {
+            listeners: {
+              stdout: (data: Buffer) => {
+                cargoPath += data.toString();
+              }
+            }
+          };
+          await exec.exec('where', ['rustup.exe'], options);
+        }
+        let rustupPath = cargoPath.split('\\').slice(0, -3).concat([".rustup"]).join("\\");
         // Github's default Windows install comes with rustup pre-installed with stable, including
         // rust-docs. This removes the default stable install so that it doesn't update rust-docs.
-    await exec.exec('rustup', ['toolchain', 'uninstall', 'stable']);
+        await renameAsync(`${rustupPath}\\toolchains`, `${rustupPath}\\_toolchains`);
+      }
+    }
   }
 }