4 files changed, 25 insertions, 6 deletions
diff --git a/std/prettier/main.ts b/std/prettier/main.ts
index cd8800d23..e3f2270c3 100755
--- a/std/prettier/main.ts
+++ b/std/prettier/main.ts
@@ -26,6 +26,7 @@
 import { parse } from "../flags/mod.ts";
 import * as path from "../path/mod.ts";
 import * as toml from "../encoding/toml.ts";
+import * as yaml from "../encoding/yaml.ts";
 import { ExpandGlobOptions, WalkInfo, expandGlob } from "../fs/mod.ts";
 import { prettier, prettierPlugins } from "./prettier.ts";
 const { args, cwd, exit, readAll, readFile, stdin, stdout, writeFile } = Deno;
@@ -393,7 +394,7 @@ async function autoResolveConfig(): Promise<PrettierBuildInOptions> {
 async function resolveConfig(
   filepath: string
 ): Promise<PrettierBuildInOptions> {
-  let config: PrettierOptions = undefined;
+  let config: PrettierBuildInOptions = undefined;
 
   function generateError(msg: string): Error {
     return new Error(`Invalid prettier configuration file: ${msg}.`);
@@ -404,18 +405,22 @@ async function resolveConfig(
   switch (path.extname(filepath)) {
     case ".json":
       try {
-        config = JSON.parse(raw) as PrettierOptions;
+        config = JSON.parse(raw) as PrettierBuildInOptions;
       } catch (err) {
         throw generateError(err.message);
       }
       break;
     case ".yml":
     case ".yaml":
-      // TODO: Unimplemented loading yaml / yml configuration file yet.
+      try {
+        config = yaml.parse(raw) as PrettierBuildInOptions;
+      } catch (err) {
+        throw generateError(err.message);
+      }
       break;
     case ".toml":
       try {
-        config = toml.parse(raw) as PrettierOptions;
+        config = toml.parse(raw) as PrettierBuildInOptions;
       } catch (err) {
         throw generateError(err.message);
       }
@@ -434,7 +439,7 @@ async function resolveConfig(
         );
 
         if (output && output.default) {
-          config = output.default;
+          config = output.default as PrettierBuildInOptions;
         } else {
           throw new Error(
             "Prettier of JS version should have default exports."
diff --git a/std/prettier/main_test.ts b/std/prettier/main_test.ts
index a63890741..dd5197e4d 100644
--- a/std/prettier/main_test.ts
+++ b/std/prettier/main_test.ts
@@ -383,7 +383,9 @@ test(async function testPrettierWithAutoConfig(): Promise<void> {
     "config_file_json",
     "config_file_toml",
     "config_file_js",
-    "config_file_ts"
+    "config_file_ts",
+    "config_file_yaml",
+    "config_file_yml"
   ];
 
   for (const configName of configs) {
@@ -441,6 +443,14 @@ test(async function testPrettierWithSpecifiedConfig(): Promise<void> {
     {
       dir: "config_file_ts",
       name: ".prettierrc.ts"
+    },
+    {
+      dir: "config_file_yaml",
+      name: ".prettierrc.yaml"
+    },
+    {
+      dir: "config_file_yml",
+      name: ".prettierrc.yml"
     }
   ];
 
diff --git a/std/prettier/testdata/config_file_yaml/.prettierrc.yaml b/std/prettier/testdata/config_file_yaml/.prettierrc.yaml
new file mode 100644
index 000000000..76e9f3104
--- /dev/null
+++ b/std/prettier/testdata/config_file_yaml/.prettierrc.yaml
@@ -0,0 +1,2 @@
+singleQuote: true
+trailingComma: "all"
diff --git a/std/prettier/testdata/config_file_yml/.prettierrc.yml b/std/prettier/testdata/config_file_yml/.prettierrc.yml
new file mode 100644
index 000000000..76e9f3104
--- /dev/null
+++ b/std/prettier/testdata/config_file_yml/.prettierrc.yml
@@ -0,0 +1,2 @@
+singleQuote: true
+trailingComma: "all"