src: do not read the next line for an empty value

When an unquoted value was empty but followed by spaces or tabs, as in
`KEY= `, the parser trimmed the newline along with the whitespace and
took the next line as the value. Strip only spaces and tabs before
checking for an empty value.

Fixes: #67400
Assisted-by: Claude Code
Signed-off-by: TseIan <tseianxwc@gmail.com>

Author: Tseian

src/node_dotenv.cc

@@ -194,6 +194,11 @@ void Dotenv::ParseContent(const std::string_view input) {
     content.remove_prefix(equal_or_newline + 1);
     key = trim_spaces(key);
 
+    // Only strip spaces and tabs here: trim_spaces() also strips '\n', which
+    // would turn the next line into the value of an empty `KEY= `.
+    content.remove_prefix(
+        std::min(content.find_first_not_of(" \t"), content.size()));
+
     // If the value is not present (e.g. KEY=) set it to an empty string
     if (content.empty() || content.front() == '\n') {
       store_.insert_or_assign(std::string(key), "");

test/parallel/test-util-parse-env.js

@@ -66,6 +66,11 @@ assert.deepStrictEqual(util.parseEnv(''), { __proto__: null });
 assert.deepStrictEqual(util.parseEnv('FOO=bar\nFOO=baz\n'),
                        { __proto__: null, FOO: 'baz' });
 
+// Whitespace after an empty value must not pull in the next line.
+// Refs: https://github.com/nodejs/node/issues/67400
+assert.deepStrictEqual(util.parseEnv('A= \nB=b\nC=\t\nD=d\nE= '),
+                       { __proto__: null, A: '', B: 'b', C: '', D: 'd', E: '' });
+
 // Test for invalid input.
 assert.throws(() => {
   for (const value of [null, undefined, {}, []]) {