Some refactoring

src/passes/Print.cpp

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 0581427..5ccef12 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -3709,29 +3709,9 @@
     doIndent(o, indent);
     o << ";; custom section \"" << section.name << "\", size "
       << section.data.size();
-    // The contents are printable if they are valid UTF-8 and all the ASCII
-    // characters are printable (non-ASCII bytes are part of multi-byte UTF-8
-    // sequences, which we emit as-is).
-    bool isPrintable = String::isUTF8(
-      std::string_view(section.data.data(), section.data.size()));
-    for (auto c : section.data) {
-      auto u = static_cast<unsigned char>(c);
-      if (u < 0x80 && !isprint(u)) {
-        isPrintable = false;
-        break;
-      }
-    }
-    if (isPrintable) {
-      o << ", contents: ";
-      // std::quoted is not available in all the supported compilers yet.
-      o << '"';
-      for (auto c : section.data) {
-        if (c == '\\' || c == '"') {
-          o << '\\';
-        }
-        o << c;
-      }
-      o << '"';
+    std::string_view sectionData(section.data.data(), section.data.size());
+    if (String::isPrintableUTF8(sectionData)) {
+      o << ", contents: " << std::quoted(sectionData);
     }
     o << maybeNewLine;
   }

src/support/string.cpp

diff --git a/src/support/string.cpp b/src/support/string.cpp
index 8e09d05..d3fbcec 100644
--- a/src/support/string.cpp
+++ b/src/support/string.cpp
@@ -484,6 +484,21 @@
   return true;
 }
 
+bool isPrintableUTF8(std::string_view str) {
+  while (!str.empty()) {
+    auto u = takeWTF8CodePoint(str);
+    if (!u) {
+      return false; // Invalid encoding
+    }
+    // Reject ASCII control chars (0x00-0x1F), DEL (0x7F), and surrogates
+    // (0xD800-0xDFFF)
+    if (*u < 0x20 || *u == 0x7F || (0xD800 <= *u && *u < 0xE000)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 std::ostream& unescapeUTF8JSONtoWTF16(std::ostream& os, const char* str) {
   std::string_view view(str);
   size_t i = 0;

src/support/string.h

diff --git a/src/support/string.h b/src/support/string.h
index 6a7617e..4e9d108 100644
--- a/src/support/string.h
+++ b/src/support/string.h
@@ -123,6 +123,10 @@
 // Whether the string is valid UTF-8.
 bool isUTF8(std::string_view str);
 
+// Whether the string is both valid UTF-8 and doesn't contain unprintable
+// characters e.g. ASCII control characters.
+bool isPrintableUTF8(std::string_view str);
+
 // Given a string of properly-escaped JSON in UTF8, unescape it into WTF16.
 std::ostream& unescapeUTF8JSONtoWTF16(std::ostream& os, const char* str);