fix(usvg): accept leading whitespace before the XML declaration

crates/usvg/Cargo.toml

@@ -47,6 +47,7 @@ unicode-vo = { version = "0.1", optional = true }
 
 [dev-dependencies]
 once_cell = "1.21"
+flate2 = { version = "1.1", default-features = false, features = ["rust_backend"] } # SVGZ encoding in tests
 
 [features]
 default = ["text", "system-fonts", "memmap-fonts"]

crates/usvg/src/parser/mod.rs

@@ -149,8 +149,14 @@ impl crate::Tree {
             ..Default::default()
         };
 
-        let doc =
-            roxmltree::Document::parse_with_options(text, xml_opt).map_err(Error::ParsingFailed)?;
+        // An XML declaration (`<?xml ?>`) is only valid as the very first thing
+        // in the document, so any leading whitespace before it makes the
+        // underlying XML parser reject the input. Trim it so that pretty-printed
+        // SVG (e.g. a string starting with a newline) parses just like its
+        // single-line form. This also benefits gzip-compressed input, which is
+        // routed through here after decompression.
+        let doc = roxmltree::Document::parse_with_options(text.trim_start(), xml_opt)
+            .map_err(Error::ParsingFailed)?;
 
         Self::from_xmltree(&doc, opt)
     }

crates/usvg/tests/parser.rs

@@ -601,3 +601,46 @@ fn flattened_text_should_inherit_absolute_transform() {
         path.abs_bounding_box()
     );
 }
+
+#[test]
+fn leading_whitespace_before_xml_declaration() {
+    // An `<?xml ?>` declaration preceded by whitespace (e.g. a string literal
+    // that starts on its own line) must still parse, matching the behavior of
+    // the same SVG without the surrounding whitespace.
+    // https://github.com/linebender/resvg/issues/1057 / iced-rs/iced#3357
+    const BODY: &str = "<svg xmlns='http://www.w3.org/2000/svg' \
+        width='10' height='10'><rect width='10' height='10'/></svg>";
+    let decl = "<?xml version='1.0' encoding='UTF-8'?>";
+
+    let opt = usvg::Options::default();
+    let parses = |s: &str| usvg::Tree::from_str(s, &opt).is_ok();
+
+    // Baselines: declaration at the very start, and no declaration at all.
+    assert!(parses(&format!("{decl}{BODY}")));
+    assert!(parses(&format!("\n  {BODY}")));
+
+    // Regression: declaration preceded by various leading whitespace.
+    assert!(parses(&format!("\n{decl}\n{BODY}")), "leading newline");
+    assert!(parses(&format!("\r\n{decl}{BODY}")), "leading CRLF");
+    assert!(parses(&format!("   {decl}{BODY}")), "leading spaces");
+    assert!(parses(&format!("\t{decl}{BODY}")), "leading tab");
+}
+
+#[test]
+fn leading_whitespace_in_gzip_compressed_svg() {
+    // The same leniency must apply to gzip-compressed input, which is routed
+    // through `from_str` after decompression.
+    use std::io::Write;
+
+    let decl = "<?xml version='1.0' encoding='UTF-8'?>";
+    let svg = format!(
+        "\n{decl}\n<svg xmlns='http://www.w3.org/2000/svg' \
+         width='10' height='10'><rect width='10' height='10'/></svg>"
+    );
+
+    let mut encoder = flate2::write::GzEncoder::new(Vec::new(), flate2::Compression::default());
+    encoder.write_all(svg.as_bytes()).unwrap();
+    let compressed = encoder.finish().unwrap();
+
+    assert!(usvg::Tree::from_data(&compressed, &usvg::Options::default()).is_ok());
+}