Add support for reading toml files

package.json

@@ -35,7 +35,8 @@
         "@actions-rs/core": "^0.1.6",
         "@actions/core": "^1.2.6",
         "@actions/exec": "^1.0.4",
-        "@actions/io": "^1.0.2"
+        "@actions/io": "^1.0.2",
+        "fast-toml": "^0.5.4"
     },
     "devDependencies": {
         "@types/jest": "^26.0.15",

src/args.ts

@@ -1,6 +1,7 @@
 import { input } from "@actions-rs/core";
 import { debug } from "@actions/core";
 import { existsSync, readFileSync } from "fs";
+import { parse } from "fast-toml";
 
 export interface ToolchainOptions {
     name: string;
@@ -36,6 +37,15 @@ function determineToolchain(overrideFile: string): string {
         flag: "r",
     }).trim();
 
+    const toolchain = rustToolchainFile.includes("[toolchain]")
+        ? parse<{ toolchain?: { channel?: string } }>(rustToolchainFile)
+              ?.toolchain?.channel
+        : rustToolchainFile;
+
+    if (!toolchain) {
+        throw new Error(`channel is not specified in ${toolchainPath}`);
+    }
+
     debug(`using toolchain from rust-toolchain file: ${rustToolchainFile}`);
 
     return rustToolchainFile;

types/fast-toml/index.d.ts

@@ -0,0 +1,9 @@
+declare module "fast-toml" {
+    export function parse<R extends Record<string, unknown>>(input: string): R;
+    export function parseFile<R extends Record<string, unknown>>(
+        file: string
+    ): Promise<R>;
+    export function parseFileSync<R extends Record<string, unknown>>(
+        file: string
+    ): R;
+}