From a2a359af36255d464e9fe79eb720d5c470eac9d6 Mon Sep 17 00:00:00 2001
From: Rogelio Guzman <rogelioguzmanh@gmail.com>
Date: Tue, 28 Nov 2017 12:54:25 -0800
Subject: [PATCH] Do not rewrite files when content did not change

---
 .../__test__/index.test.js                    | 44 +++++++++++++++++++
 .../css-modules-flow-types-loader/index.js    | 15 ++++++-
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/packages/css-modules-flow-types-loader/__test__/index.test.js b/packages/css-modules-flow-types-loader/__test__/index.test.js
index f54f3be..be92f2d 100644
--- a/packages/css-modules-flow-types-loader/__test__/index.test.js
+++ b/packages/css-modules-flow-types-loader/__test__/index.test.js
@@ -69,6 +69,50 @@ declare module.exports: {|
       `${HEADER}
 declare module.exports: {|
 
+|};
+`
+    );
+  });
+
+  it('does not emit a css.flow file if the file exists and has the same contents', () => {
+    fs.existsSync.mockImplementationOnce(
+      filePath => filePath === 'test.css.flow'
+    );
+
+    loader.call(
+      {
+        resourcePath: 'test.css',
+      },
+      STYLE_LOADER_OUTPUT
+    );
+
+    expect(fs.writeFile.mock.calls.length).toBe(0);
+  });
+
+  it('emits a css.flow file if the file exists and has the different contents', () => {
+    fs.existsSync.mockImplementationOnce(
+      filePath => filePath === 'test.css.flow'
+    );
+
+    fs.readFile.mockImplementationOnce((filePath, opts, cb) => {
+      if (filePath === 'test.css.flow') {
+        cb(null, 'Other content');
+      }
+    });
+    loader.call(
+      {
+        resourcePath: 'test.css',
+      },
+      STYLE_LOADER_OUTPUT
+    );
+
+    expect(fs.writeFile.mock.calls.length).toBe(1);
+    expect(fs.writeFile.mock.calls[0][0]).toBe('test.css.flow');
+
+    expect(fs.writeFile.mock.calls[0][1]).toBe(
+      `${HEADER}
+declare module.exports: {|
+  +'btn': string;
 |};
 `
     );
diff --git a/packages/css-modules-flow-types-loader/index.js b/packages/css-modules-flow-types-loader/index.js
index 084a066..59f3916 100644
--- a/packages/css-modules-flow-types-loader/index.js
+++ b/packages/css-modules-flow-types-loader/index.js
@@ -25,7 +25,20 @@ module.exports = function cssModulesFlowTypesLoader(content) {
   // NOTE: We cannot use .emitFile as people might use this with devServer
   // (e.g. in memory storage).
   const outputPath = this.resourcePath + '.flow';
-  fs.writeFile(outputPath, printFlowDefinition(tokens), {}, function() {});
+  const newContent = printFlowDefinition(tokens);
+  if (fs.existsSync(outputPath)) {
+    fs.readFile(outputPath, 'utf8', function(err, currentContent) {
+      if (err) {
+        throw err;
+      }
+
+      if (currentContent !== newContent) {
+        fs.writeFile(outputPath, newContent, {}, function() {});
+      }
+    });
+  } else {
+    fs.writeFile(outputPath, newContent, {}, function() {});
+  }
 
   return content;
 };