test: Add a test for source highlighting

examples/highlight_source.rs

@@ -0,0 +1,34 @@
+use annotate_snippets::{AnnotationKind, Group, Level, Renderer, Snippet};
+
+fn main() {
+    let source = r#"//@ compile-flags: -Z teach
+
+#![allow(warnings)]
+
+const CON: Vec<i32> = vec![1, 2, 3]; //~ ERROR E0010
+//~| ERROR cannot call non-const method
+fn main() {}
+"#;
+    let message = Level::Error
+        .message("allocations are not allowed in constants")
+        .id("E0010")
+        .group(
+            Group::new()
+                .element(
+                    Snippet::source(source)
+                        .fold(true)
+                        .origin("$DIR/E0010-teach.rs")
+                        .annotation(
+                            AnnotationKind::Primary
+                                .span(72..85)
+                                .label("allocation not allowed in constants")
+                        ),
+                )
+                .element(
+                    Level::Note.title("The runtime heap is not yet available at compile-time, so no runtime heap allocations can be created."),
+                ),
+        );
+
+    let renderer = Renderer::styled().anonymized_line_numbers(true);
+    anstream::println!("{}", renderer.render(message));
+}

tests/examples.rs

@@ -19,6 +19,13 @@ fn format() {
     assert_example(target, expected);
 }
 
+#[test]
+fn highlight_source() {
+    let target = "highlight_source";
+    let expected = snapbox::file!["../examples/highlight_source.svg": TermSvg];
+    assert_example(target, expected);
+}
+
 #[test]
 fn multislice() {
     let target = "multislice";