fix(dlint): avoid panic when no trailing new line is appended (#1149)

This commit prevents dlint from panicking when the input file doesn't contain a final newline character.

Towards #1145

examples/dlint/diagnostics.rs

@@ -134,7 +134,9 @@ impl miette::SourceCode for MietteSourceCode<'_> {
       end_line_column.line_index + context_lines_after,
       self.source.text_str().len(),
     );
-    let src_end = self.source.line_end(end_line_index);
+    let src_end = self
+      .source
+      .line_end(std::cmp::min(end_line_index, line_count - 1));
     let range = SourceRange::new(src_start, src_end);
     let src_text = range.text_fast(&self.source);
     let byte_range = range.as_byte_range(start_pos);

examples/dlint/main.rs

@@ -425,4 +425,10 @@ mod tests {
     output: "simple.out",
     exit_code: 1,
   });
+
+  itest!(issue1145_no_trailing_newline {
+    args: "run issue1145_no_trailing_newline.ts",
+    output: "issue1145_no_trailing_newline.out",
+    exit_code: 1,
+  });
 }

examples/dlint/testdata/issue1145_no_trailing_newline.out

@@ -0,0 +1,22 @@
+no-unused-vars
+
+  x `base` is never used
+   ,-[issue1145_no_trailing_newline.ts:3:5]
+ 3 | ---*/
+ 4 | var base
+   :     ^^|^
+   :       `-- If this is intentional, prefix it with an underscore like `_base`
+   `----
+  help: https://lint.deno.land/#no-unused-vars
+
+no-var
+
+  x `var` keyword is not allowed.
+   ,-[issue1145_no_trailing_newline.ts:3:1]
+ 3 | ---*/
+ 4 | var base
+   : ^^^^^^^^
+   `----
+  help: https://lint.deno.land/#no-var
+
+Found 2 problems

examples/dlint/testdata/issue1145_no_trailing_newline.ts

@@ -0,0 +1,3 @@
+/*---
+---*/
+var base