Formatter: add support for any Unicode scalar value in source text

src/format.rs

@@ -124,17 +124,7 @@ impl<'a> Formatter<'a> {
     }
 
     pub fn write_quoted(&mut self, s: &str) {
-        let mut has_newline = false;
-        let mut has_nonprintable = false;
-        for c in s.chars() {
-            match c {
-                '\n' => has_newline = true,
-                '\r' | '\t' | '\u{0020}'..='\u{FFFF}' => {}
-                _ => has_nonprintable = true,
-            }
-        }
-        if !has_newline || has_nonprintable {
-            use std::fmt::Write;
+        if !s.contains('\n') {
             self.buf.push('"');
             for c in s.chars() {
                 match c {
@@ -143,8 +133,9 @@ impl<'a> Formatter<'a> {
                     '\t' => self.write(r"\t"),
                     '"' => self.write("\\\""),
                     '\\' => self.write(r"\\"),
-                    '\u{0020}'..='\u{FFFF}' => self.buf.push(c),
-                    _ => write!(&mut self.buf, "\\u{:04}", c as u32).unwrap(),
+                    // This covers all Unicode scalar values (range U+0000..=U+D7FF | U+E000..=U+10FFFF)
+                    // as permitted by Rust's char type and GraphQL's (September 2025 version) SourceCharacter 
+                    _ => self.buf.push(c),
                 }
             }
             self.buf.push('"');

tests/queries/directive_args.graphql

@@ -1,3 +1,3 @@
 query {
-  node @dir(a: 1, b: "2", c: true, d: false, e: null)
+  node @dir(a: 1, b: "2 🤓", c: true, d: false, e: null)
 }

tests/queries/directive_args_multiline.graphql

@@ -1,7 +1,7 @@
 query {
   node @dir(
     a: 1,
-    b: "2",
+    b: "2 🤓",
     c: true,
     d: false,
     e: null

tests/queries/query_var_default_string.graphql

@@ -1,3 +1,3 @@
-query Foo($site: String = "string") {
+query Foo($site: String = "string 🤓") {
   field
 }

tests/queries/string_literal.graphql

@@ -1,3 +1,3 @@
 query {
-  node(id: "hello")
+  node(id: "hello 🤓")
 }

tests/queries/triple_quoted_literal.graphql

@@ -1,6 +1,6 @@
 query {
   node(id: """
-    Hello,
+    Hello 🤓,
       world!
   """)
 }