fs: runtime deprecate string coercion in `fs.write`, `fs.writeFileSync`

This also affects `fs.writeFile`, `fs.appendFile`, and
`fs.appendFileSync`

PR-URL: https://github.com/nodejs/node/pull/42607
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/lib/fs.js b/lib/fs.js
index 417fff0dedc..405c206d566 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -163,6 +163,11 @@ const isWindows = process.platform === 'win32';
 const isOSX = process.platform === 'darwin';
 
 
+const showStringCoercionDeprecation = internalUtil.deprecate(
+  () => {},
+  'Implicit coercion of objects with own toString property is deprecated.',
+  'DEP0162'
+);
 function showTruncateDeprecation() {
   if (truncateWarn) {
     process.emitWarning(
@@ -826,6 +831,9 @@ function write(fd, buffer, offset, length, position, callback) {
   }
 
   validateStringAfterArrayBufferView(buffer, 'buffer');
+  if (typeof buffer !== 'string') {
+    showStringCoercionDeprecation();
+  }
 
   if (typeof position !== 'function') {
     if (typeof offset === 'function') {
@@ -2121,6 +2129,9 @@ function writeFile(path, data, options, callback) {
 
   if (!isArrayBufferView(data)) {
     validateStringAfterArrayBufferView(data, 'data');
+    if (typeof data !== 'string') {
+      showStringCoercionDeprecation();
+    }
     data = Buffer.from(String(data), options.encoding || 'utf8');
   }
 
@@ -2161,6 +2172,9 @@ function writeFileSync(path, data, options) {
 
   if (!isArrayBufferView(data)) {
     validateStringAfterArrayBufferView(data, 'data');
+    if (typeof data !== 'string') {
+      showStringCoercionDeprecation();
+    }
     data = Buffer.from(String(data), options.encoding || 'utf8');
   }