Prevent panic when span points past end of line.

src/lib.rs

@@ -108,8 +108,13 @@ fn parse_snippet(span: &DiagnosticSpan) -> Option<Snippet> {
     let text_slice = span.text[0].text.chars().collect::<Vec<char>>();
 
     // We subtract `1` because these highlights are 1-based
-    let start = span.text[0].highlight_start - 1;
-    let end = span.text[0].highlight_end - 1;
+    // Check the `min` so that it doesn't attempt to index out-of-bounds when
+    // the span points to the "end" of the line. For example, a line of
+    // "foo\n" with a highlight_start of 5 is intended to highlight *after*
+    // the line. This needs to compensate since the newline has been removed
+    // from the text slice.
+    let start = (span.text[0].highlight_start - 1).min(text_slice.len());
+    let end = (span.text[0].highlight_end - 1).min(text_slice.len());
     let lead = text_slice[indent..start].iter().collect();
     let mut body: String = text_slice[start..end].iter().collect();
 

tests/edge-cases/no_main.json

@@ -0,0 +1,33 @@
+{
+  "message": "`main` function not found in crate `no_main`",
+  "code": {
+    "code": "E0601",
+    "explanation": "No `main` function was found in a binary crate. To fix this error, add a\n`main` function. For example:\n\n```\nfn main() {\n    // Your program will start here.\n    println!(\"Hello world!\");\n}\n```\n\nIf you don't know the basics of Rust, you can go look to the Rust Book to get\nstarted: https://doc.rust-lang.org/book/\n"
+  },
+  "level": "error",
+  "spans": [
+    {
+      "file_name": "no_main.rs",
+      "byte_start": 26,
+      "byte_end": 26,
+      "line_start": 1,
+      "line_end": 1,
+      "column_start": 27,
+      "column_end": 27,
+      "is_primary": true,
+      "text": [
+        {
+          "text": "// This file has no main.",
+          "highlight_start": 27,
+          "highlight_end": 27
+        }
+      ],
+      "label": "consider adding a `main` function to `no_main.rs`",
+      "suggested_replacement": null,
+      "suggestion_applicability": null,
+      "expansion": null
+    }
+  ],
+  "children": [],
+  "rendered": "error[E0601]: `main` function not found in crate `no_main`\n --> no_main.rs:1:27\n  |\n1 | // This file has no main.\n  |                           ^ consider adding a `main` function to `no_main.rs`\n\n"
+}

tests/edge-cases/no_main.rs

@@ -0,0 +1 @@
+// This file has no main.

tests/edge_cases.rs

@@ -22,3 +22,4 @@ expect_empty_json_test! {multiple_fix_options_yield_no_suggestions, "skip-multi-
 expect_empty_json_test! {out_of_bounds_test, "out_of_bounds.recorded.json"}
 expect_empty_json_test! {utf8_identifiers_test, "utf8_idents.recorded.json"}
 expect_empty_json_test! {empty, "empty.json"}
+expect_empty_json_test! {no_main, "no_main.json"}