Auto merge of #103185 - chenyukang:yukang/fix-span-next-point, r=davidtwco

Fix the bug of next_point in source_map

There is a bug in `next_point`, the new span won't move to next position when be called in the first time.

For this reason, our current code is working like this:
1. When we really want to move to the next position, we called two times of `next_point`
2. Some code which use `next_point` actually done the same thing with `shrink_to_hi`

This fix make sure when `next_point` is called, span will move with the width at least 1, and also work correctly in the scenario of multiple bytes.

Ref: #103140 (comment)

r? `@davidtwco`

Author: bors

compiler/rustc_expand/src/expand.rs

@@ -937,13 +937,12 @@ pub fn ensure_complete_parse<'a>(
             kind_name,
         );
         err.note(&msg);
-        let semi_span = this.sess.source_map().next_point(span);
 
-        let semi_full_span = semi_span.to(this.sess.source_map().next_point(semi_span));
-        match this.sess.source_map().span_to_snippet(semi_full_span) {
+        let semi_span = this.sess.source_map().next_point(span);
+        match this.sess.source_map().span_to_snippet(semi_span) {
             Ok(ref snippet) if &snippet[..] != ";" && kind_name == "expression" => {
                 err.span_suggestion(
-                    semi_span,
+                    span.shrink_to_hi(),
                     "you might be missing a semicolon here",
                     ";",
                     Applicability::MaybeIncorrect,

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -82,7 +82,7 @@ fn emit_frag_parse_err(
         );
         if !e.span.is_dummy() {
             // early end of macro arm (#52866)
-            e.replace_span_with(parser.sess.source_map().next_point(parser.token.span));
+            e.replace_span_with(parser.token.span.shrink_to_hi());
         }
     }
     if e.span.is_dummy() {

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1461,7 +1461,7 @@ impl<'a> Parser<'a> {
         let (prev_sp, sp) = match (&self.token.kind, self.subparser_name) {
             // Point at the end of the macro call when reaching end of macro arguments.
             (token::Eof, Some(_)) => {
-                let sp = self.sess.source_map().next_point(self.prev_token.span);
+                let sp = self.prev_token.span.shrink_to_hi();
                 (sp, sp)
             }
             // We don't want to point at the following span after DUMMY_SP.
@@ -2039,7 +2039,7 @@ impl<'a> Parser<'a> {
     pub(super) fn expected_expression_found(&self) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         let (span, msg) = match (&self.token.kind, self.subparser_name) {
             (&token::Eof, Some(origin)) => {
-                let sp = self.sess.source_map().next_point(self.prev_token.span);
+                let sp = self.prev_token.span.shrink_to_hi();
                 (sp, format!("expected expression, found end of {origin}"))
             }
             _ => (

compiler/rustc_parse/src/parser/expr.rs

@@ -2172,7 +2172,7 @@ impl<'a> Parser<'a> {
                     },
                 ExprKind::Block(_, None) => {
                     self.sess.emit_err(IfExpressionMissingCondition {
-                        if_span: self.sess.source_map().next_point(lo),
+                        if_span: lo.shrink_to_hi(),
                         block_span: self.sess.source_map().start_point(cond_span),
                     });
                     std::mem::replace(&mut cond, this.mk_expr_err(cond_span.shrink_to_hi()))

compiler/rustc_parse/src/parser/item.rs

@@ -1601,7 +1601,7 @@ impl<'a> Parser<'a> {
                     self.sess.emit_err(err);
                 } else {
                     if !seen_comma {
-                        let sp = self.sess.source_map().next_point(previous_span);
+                        let sp = previous_span.shrink_to_hi();
                         err.missing_comma = Some(sp);
                     }
                     return Err(err.into_diagnostic(&self.sess.span_diagnostic));

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1731,7 +1731,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                             for _ in 0..100 {
                                 // Try to find an assignment
                                 sp = sm.next_point(sp);
-                                let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
+                                let snippet = sm.span_to_snippet(sp);
                                 match snippet {
                                     Ok(ref x) if x.as_str() == "=" => {
                                         err.span_suggestion(

compiler/rustc_span/src/source_map.rs

@@ -853,28 +853,36 @@ impl SourceMap {
     }
 
     /// Returns a new span representing the next character after the end-point of this span.
+    /// Special cases:
+    /// - if span is a dummy one, returns the same span
+    /// - if next_point reached the end of source, return span with lo = hi
+    /// - respect multi-byte characters
     pub fn next_point(&self, sp: Span) -> Span {
         if sp.is_dummy() {
             return sp;
         }
         let start_of_next_point = sp.hi().0;
 
-        let width = self.find_width_of_character_at_span(sp.shrink_to_hi(), true);
-        // If the width is 1, then the next span should point to the same `lo` and `hi`. However,
-        // in the case of a multibyte character, where the width != 1, the next span should
+        let width = self.find_width_of_character_at_span(sp, true);
+        if width == 0 {
+            return Span::new(sp.hi(), sp.hi(), sp.ctxt(), None);
+        }
+        // If the width is 1, then the next span should only contain the next char besides current ending.
+        // However, in the case of a multibyte character, where the width != 1, the next span should
         // span multiple bytes to include the whole character.
         let end_of_next_point =
-            start_of_next_point.checked_add(width - 1).unwrap_or(start_of_next_point);
+            start_of_next_point.checked_add(width).unwrap_or(start_of_next_point);
 
-        let end_of_next_point = BytePos(cmp::max(sp.lo().0 + 1, end_of_next_point));
+        let end_of_next_point = BytePos(cmp::max(start_of_next_point + 1, end_of_next_point));
         Span::new(BytePos(start_of_next_point), end_of_next_point, sp.ctxt(), None)
     }
 
     /// Finds the width of the character, either before or after the end of provided span,
     /// depending on the `forwards` parameter.
     fn find_width_of_character_at_span(&self, sp: Span, forwards: bool) -> u32 {
         let sp = sp.data();
-        if sp.lo == sp.hi {
+
+        if sp.lo == sp.hi && !forwards {
             debug!("find_width_of_character_at_span: early return empty span");
             return 1;
         }
@@ -908,9 +916,9 @@ impl SourceMap {
         let source_len = (local_begin.sf.end_pos - local_begin.sf.start_pos).to_usize();
         debug!("find_width_of_character_at_span: source_len=`{:?}`", source_len);
         // Ensure indexes are also not malformed.
-        if start_index > end_index || end_index > source_len {
+        if start_index > end_index || end_index > source_len - 1 {
             debug!("find_width_of_character_at_span: source indexes are malformed");
-            return 1;
+            return 0;
         }
 
         let src = local_begin.sf.external_src.borrow();

compiler/rustc_span/src/source_map/tests.rs

@@ -479,3 +479,48 @@ fn path_prefix_remapping_expand_to_absolute() {
         RealFileName::Remapped { local_path: None, virtual_name: path("XYZ/src/main.rs") }
     );
 }
+
+#[test]
+fn test_next_point() {
+    let sm = SourceMap::new(FilePathMapping::empty());
+    sm.new_source_file(PathBuf::from("example.rs").into(), "a…b".to_string());
+
+    // Dummy spans don't advance.
+    let span = DUMMY_SP;
+    let span = sm.next_point(span);
+    assert_eq!(span.lo().0, 0);
+    assert_eq!(span.hi().0, 0);
+
+    // Span advance respect multi-byte character
+    let span = Span::with_root_ctxt(BytePos(0), BytePos(1));
+    assert_eq!(sm.span_to_snippet(span), Ok("a".to_string()));
+    let span = sm.next_point(span);
+    assert_eq!(sm.span_to_snippet(span), Ok("…".to_string()));
+    assert_eq!(span.lo().0, 1);
+    assert_eq!(span.hi().0, 4);
+
+    // An empty span pointing just before a multi-byte character should
+    // advance to contain the multi-byte character.
+    let span = Span::with_root_ctxt(BytePos(1), BytePos(1));
+    let span = sm.next_point(span);
+    assert_eq!(span.lo().0, 1);
+    assert_eq!(span.hi().0, 4);
+
+    let span = Span::with_root_ctxt(BytePos(1), BytePos(4));
+    let span = sm.next_point(span);
+    assert_eq!(span.lo().0, 4);
+    assert_eq!(span.hi().0, 5);
+
+    // A non-empty span at the last byte should advance to create an empty
+    // span pointing at the end of the file.
+    let span = Span::with_root_ctxt(BytePos(4), BytePos(5));
+    let span = sm.next_point(span);
+    assert_eq!(span.lo().0, 5);
+    assert_eq!(span.hi().0, 5);
+
+    // Empty span pointing just past the last byte.
+    let span = Span::with_root_ctxt(BytePos(5), BytePos(5));
+    let span = sm.next_point(span);
+    assert_eq!(span.lo().0, 5);
+    assert_eq!(span.hi().0, 5);
+}

src/tools/clippy/clippy_utils/src/sugg.rs

@@ -769,8 +769,7 @@ impl<T: LintContext> DiagnosticExt<T> for rustc_errors::Diagnostic {
 
     fn suggest_remove_item(&mut self, cx: &T, item: Span, msg: &str, applicability: Applicability) {
         let mut remove_span = item;
-        let hi = cx.sess().source_map().next_point(remove_span).hi();
-        let fmpos = cx.sess().source_map().lookup_byte_offset(hi);
+        let fmpos = cx.sess().source_map().lookup_byte_offset(remove_span.hi());
 
         if let Some(ref src) = fmpos.sf.src {
             let non_whitespace_offset = src[fmpos.pos.to_usize()..].find(|c| c != ' ' && c != '\t' && c != '\n');