Fix generated JS output to not insert indentation characters inside multiline `` strings.

src/parseTools.mjs

@@ -331,14 +331,39 @@ function splitI64(value) {
 export function indentify(text, indent) {
   // Don't try to indentify huge strings - we may run out of memory
   if (text.length > 1024 * 1024) return text;
-  if (typeof indent == 'number') {
-    const len = indent;
-    indent = '';
-    for (let i = 0; i < len; i++) {
-      indent += ' ';
+
+  indent = ' '.repeat(indent);
+
+  // Perform indentation in a smart fashion that does not leak indentation
+  // inside multiline strings enclosed in `` characters.
+  let out = '';
+  for (let i = 0; i < text.length; ++i) {
+    // Output a C++ comment as-is, don't get confused by ` inside a C++ comment.
+    if (text[i] == '/' && text[i + 1] == '/') {
+      for (; i < text.length && text[i] != '\n'; ++i) {
+        out += text[i];
+      }
+    }
+
+    if (text[i] == '/' && text[i + 1] == '*') {
+      // Skip /* so that /*/ won't be mistaken as start& end of a /* */ comment.
+      out += text[i++];
+      out += text[i++];
+      for (; i < text.length && !(text[i - 1] == '*' && text[i] == '/'); ++i) {
+        out += text[i];
+      }
+    }
+
+    if (text[i] == '`') {
+      out += text[i++]; // Emit `
+      for (; i < text.length && text[i] != '`'; ++i) {
+        out += text[i];
+      }
     }
+    out += text[i];
+    if (text[i] == '\n') out += indent;
   }
-  return text.replace(/\n/g, `\n${indent}`);
+  return out;
 }
 
 // Correction tools

test/jslib/test_multiline_string.c

@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+char *test_multiline_string(void);
+
+int main() {
+  char *str = test_multiline_string();
+  printf("%s\n", str);
+  free(str);
+}

test/jslib/test_multiline_string.js

@@ -0,0 +1,15 @@
+mergeInto(LibraryManager.library, {
+  test_multiline_string__deps: ['$stringToNewUTF8'],
+  test_multiline_string__sig: 'p',
+  test_multiline_string: function() {
+    // do not get confused by ` inside a comment.
+    var a = `abc
+def
+ghi`;
+    /* or a ` inside a C comment. */
+    var b = `abc
+def
+ghi`;
+    return stringToNewUTF8(a + b);
+  }
+});

test/jslib/test_multiline_string.out

@@ -0,0 +1,5 @@
+abc
+def
+ghiabc
+def
+ghi

test/test_jslib.py

@@ -748,3 +748,12 @@ class ParentClass {}
       }
     ''')
     self.do_runf('src.c', 'MyClass: 42', cflags=['--js-library', 'lib.js'])
+
+  # Tests that JS library functions containing multiline strings are not disturbed by e.g. inserting indentation into the output.
+  @parameterized({
+    '': ([],),
+    'single_file': (['-sSINGLE_FILE'],),
+    'closure': (['--closure', '1'],),
+  })
+  def test_multiline_string(self, args):
+    self.do_run_in_out_file_test('jslib/test_multiline_string.c', cflags=['--js-library', test_file('jslib/test_multiline_string.js')] + args)