Fix SourceFile::normalized_byte_pos

This method was broken by 258ace6, which changed `self.normalized_pos`
to use relative offsets however this method continued to compare against
an absolute offset.

Also adds a regression test for the issue that this method was
originally introduced to fix.

compiler/rustc_span/src/lib.rs

@@ -2426,14 +2426,12 @@ impl SourceFile {
     /// normalized one. Hence we need to convert those offsets to the normalized
     /// form when constructing spans.
     pub fn normalized_byte_pos(&self, offset: u32) -> BytePos {
-        let diff = match self
-            .normalized_pos
-            .binary_search_by(|np| (np.pos.0 + np.diff).cmp(&(self.start_pos.0 + offset)))
-        {
-            Ok(i) => self.normalized_pos[i].diff,
-            Err(0) => 0,
-            Err(i) => self.normalized_pos[i - 1].diff,
-        };
+        let diff =
+            match self.normalized_pos.binary_search_by(|np| (np.pos.0 + np.diff).cmp(&offset)) {
+                Ok(i) => self.normalized_pos[i].diff,
+                Err(0) => 0,
+                Err(i) => self.normalized_pos[i - 1].diff,
+            };
 
         BytePos::from_u32(self.start_pos.0 + offset - diff)
     }

src/tools/tidy/src/ui_tests.rs

@@ -150,6 +150,7 @@ fn check_unexpected_extension(check: &mut RunningCheck, file_path: &Path, ext: &
 
     const EXTENSION_EXCEPTION_PATHS: &[&str] = &[
         "tests/ui/asm/named-asm-labels.s", // loading an external asm file to test named labels lint
+        "tests/ui/asm/normalize-offsets-for-crlf.s", // loading an external asm file to test CRLF normalization
         "tests/ui/codegen/mismatched-data-layout.json", // testing mismatched data layout w/ custom targets
         "tests/ui/check-cfg/my-awesome-platform.json",  // testing custom targets with cfgs
         "tests/ui/argfile/commandline-argfile-badutf8.args", // passing args via a file

tests/ui/asm/.gitattributes

@@ -0,0 +1,2 @@
+# Disable EOL normalization, as it is deliberately denormalized
+normalize-offsets-for-crlf.s -text

tests/ui/asm/normalize-offsets-for-crlf.rs

@@ -0,0 +1,14 @@
+// Byte positions into inline assembly reported by codegen errors require normalization or else
+// they may not identify the appropriate span.  Worse still, an ICE can occur if the erroneous
+// span begins or ends part-way through a multibyte character.
+//
+// Regression test for https://github.com/rust-lang/rust/issues/110885
+
+// This test is tied to assembler syntax and errors, which can vary by backend and architecture.
+//@only-x86_64
+//@needs-backends: llvm
+//@build-fail
+
+//~? ERROR instruction mnemonic
+std::arch::global_asm!(include_str!("normalize-offsets-for-crlf.s"));
+fn main() {}

tests/ui/asm/normalize-offsets-for-crlf.s

@@ -0,0 +1,13 @@
+// This file contains (some) CRLF line endings.  When codegen reports an error, the byte
+// offsets into this file that it identifies require normalization or else they will not
+// identify the appropriate span.  Worse still, an ICE can result if the erroneous span
+// begins or ends part-way through a multibyte character such as £.
+non_existent_mnemonic
+
+// Without normalization, the three CRLF line endings below cause the diagnostic on the
+// `non_existent_mnemonic` above to be spanned three bytes backward, and thus begin
+// part-way inside the multibyte character in the preceding comment.
+//
+// NOTE: The lines of this note DELIBERATELY end with CRLF - DO NOT strip/convert them!
+//       It may not be obvious if you accidentally do, eg `git diff` may appear to show
+//       that the lines have been updated to the exact same content.

tests/ui/asm/normalize-offsets-for-crlf.stderr

@@ -0,0 +1,10 @@
+error: invalid instruction mnemonic 'non_existent_mnemonic'
+   |
+note: instantiated into assembly here
+  --> <inline asm>:6:1
+   |
+LL | non_existent_mnemonic
+   | ^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+