Fix some panics in edge cases.

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();
 
@@ -122,7 +127,8 @@ fn parse_snippet(span: &DiagnosticSpan) -> Option<Snippet> {
 
     // If we get a DiagnosticSpanLine where highlight_end > text.len(), we prevent an 'out of
     // bounds' access by making sure the index is within the array bounds.
-    let last_tail_index = last.highlight_end.min(last.text.len()) - 1;
+    // `saturating_sub` is used in case of an empty file
+    let last_tail_index = last.highlight_end.min(last.text.len()).saturating_sub(1);
     let last_slice = last.text.chars().collect::<Vec<char>>();
 
     if span.text.len() > 1 {

tests/edge-cases/empty.json

@@ -0,0 +1,42 @@
+{
+  "message": "`main` function not found in crate `empty`",
+  "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": "empty.rs",
+      "byte_start": 0,
+      "byte_end": 0,
+      "line_start": 0,
+      "line_end": 0,
+      "column_start": 1,
+      "column_end": 1,
+      "is_primary": true,
+      "text": [
+        {
+          "text": "",
+          "highlight_start": 1,
+          "highlight_end": 1
+        }
+      ],
+      "label": null,
+      "suggested_replacement": null,
+      "suggestion_applicability": null,
+      "expansion": null
+    }
+  ],
+  "children": [
+    {
+      "message": "consider adding a `main` function to `empty.rs`",
+      "code": null,
+      "level": "note",
+      "spans": [],
+      "children": [],
+      "rendered": null
+    }
+  ],
+  "rendered": "error[E0601]: `main` function not found in crate `empty`\n  |\n  = note: consider adding a `main` function to `empty.rs`\n\n"
+}

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

@@ -2,29 +2,24 @@ use rustfix;
 use std::collections::HashSet;
 use std::fs;
 
-#[test]
-fn multiple_fix_options_yield_no_suggestions() {
-    let json = fs::read_to_string("./tests/edge-cases/skip-multi-option-lints.json").unwrap();
-    let expected_suggestions =
-        rustfix::get_suggestions_from_json(&json, &HashSet::new(), rustfix::Filter::Everything)
+macro_rules! expect_empty_json_test {
+    ($name:ident, $file:expr) => {
+        #[test]
+        fn $name() {
+            let json = fs::read_to_string(concat!("./tests/edge-cases/", $file)).unwrap();
+            let expected_suggestions = rustfix::get_suggestions_from_json(
+                &json,
+                &HashSet::new(),
+                rustfix::Filter::Everything,
+            )
             .unwrap();
-    assert!(expected_suggestions.is_empty());
+            assert!(expected_suggestions.is_empty());
+        }
+    };
 }
 
-#[test]
-fn out_of_bounds_test() {
-    let json = fs::read_to_string("./tests/edge-cases/out_of_bounds.recorded.json").unwrap();
-    let expected_suggestions =
-        rustfix::get_suggestions_from_json(&json, &HashSet::new(), rustfix::Filter::Everything)
-            .unwrap();
-    assert!(expected_suggestions.is_empty());
-}
-
-#[test]
-fn utf8_identifiers_test() {
-    let json = fs::read_to_string("./tests/edge-cases/utf8_idents.recorded.json").unwrap();
-    let expected_suggestions =
-        rustfix::get_suggestions_from_json(&json, &HashSet::new(), rustfix::Filter::Everything)
-            .unwrap();
-    assert!(expected_suggestions.is_empty());
-}
+expect_empty_json_test! {multiple_fix_options_yield_no_suggestions, "skip-multi-option-lints.json"}
+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"}

tests/parse_and_replace.rs

@@ -54,6 +54,9 @@ fn compile(file: &Path, mode: &str) -> Result<Output, Error> {
 fn compile_and_get_json_errors(file: &Path, mode: &str) -> Result<String, Error> {
     let res = compile(file, mode)?;
     let stderr = String::from_utf8(res.stderr)?;
+    if stderr.contains("is only accepted on the nightly compiler") {
+        panic!("rustfix tests require a nightly compiler");
+    }
 
     match res.status.code() {
         Some(0) | Some(1) | Some(101) => Ok(stderr),
@@ -160,7 +163,7 @@ fn test_rustfix_with_file<P: AsRef<Path>>(file: P, mode: &str) -> Result<(), Err
         ))?;
         let expected_suggestions =
             rustfix::get_suggestions_from_json(&expected_json, &HashSet::new(), filter_suggestions)
-                .context("could not load expected suggesitons")?;
+                .context("could not load expected suggestions")?;
 
         ensure!(
             expected_suggestions == suggestions,