Fix ICE in undocumented_unsafe_blocks

clippy_lints/src/undocumented_unsafe_blocks.rs

@@ -149,6 +149,8 @@ impl UndocumentedUnsafeBlocks {
         let lex_end = (between_span.hi().0 - source_file.start_pos.0) as usize;
         let src_str = source_file.src.as_ref()?[lex_start..lex_end].to_string();
 
+        let source_start_pos = source_file.start_pos.0 as usize + lex_start;
+
         let mut pos = 0;
         let mut comment = false;
 
@@ -171,7 +173,7 @@ impl UndocumentedUnsafeBlocks {
                     if comment {
                         // Get the line number of the "comment" (really wherever the trailing whitespace ended)
                         let comment_line_num = source_file
-                            .lookup_file_pos_with_col_display(BytePos((lex_start + pos).try_into().unwrap()))
+                            .lookup_file_pos(BytePos((source_start_pos + pos).try_into().unwrap()))
                             .0;
                         // Find the block/local's line number
                         let block_line_num = tcx.sess.source_map().lookup_char_pos(block_span.lo()).line;

tests/ui/crashes/auxiliary/ice-7934-aux.rs

@@ -0,0 +1,4 @@
+fn zero() {
+    // SAFETY:
+    unsafe { 0 };
+}

tests/ui/crashes/ice-7934.rs

@@ -0,0 +1,7 @@
+#![warn(clippy::undocumented_unsafe_blocks)]
+#![allow(clippy::no_effect)]
+
+#[path = "auxiliary/ice-7934-aux.rs"]
+mod zero;
+
+fn main() {}