Rollup merge of #66025 - petrochenkov:lohi, r=eddyb

`Span` cannot represent `span.hi < span.lo`

So we can remove the corresponding checks from various code

Author: pietroalbini

src/librustc/ich/hcx.rs

@@ -309,11 +309,6 @@ impl<'a> HashStable<StableHashingContext<'a>> for Span {
         // position that belongs to it, as opposed to hashing the first
         // position past it.
         let span = self.data();
-
-        if span.hi < span.lo {
-            return std_hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
-        }
-
         let (file_lo, line_lo, col_lo) = match hcx.source_map()
                                                   .byte_pos_to_line_and_col(span.lo) {
             Some(pos) => pos,

src/librustc/ty/query/on_disk_cache.rs

@@ -796,11 +796,6 @@ where
         }
 
         let span_data = span.data();
-
-        if span_data.hi < span_data.lo {
-            return TAG_INVALID_SPAN.encode(self);
-        }
-
         let (file_lo, line_lo, col_lo) = match self.source_map
                                                    .byte_pos_to_line_and_col(span_data.lo) {
             Some(pos) => pos,

src/libsyntax/parse/lexer/mod.rs

@@ -68,7 +68,7 @@ impl<'a> StringReader<'a> {
         let end = sess.source_map().lookup_byte_offset(span.hi());
 
         // Make the range zero-length if the span is invalid.
-        if span.lo() > span.hi() || begin.sf.start_pos != end.sf.start_pos {
+        if begin.sf.start_pos != end.sf.start_pos {
             span = span.shrink_to_lo();
         }
 

src/libsyntax/source_map.rs

@@ -498,10 +498,6 @@ impl SourceMap {
     pub fn span_to_lines(&self, sp: Span) -> FileLinesResult {
         debug!("span_to_lines(sp={:?})", sp);
 
-        if sp.lo() > sp.hi() {
-            return Err(SpanLinesError::IllFormedSpan(sp));
-        }
-
         let lo = self.lookup_char_pos(sp.lo());
         debug!("span_to_lines: lo={:?}", lo);
         let hi = self.lookup_char_pos(sp.hi());
@@ -549,10 +545,6 @@ impl SourceMap {
     fn span_to_source<F>(&self, sp: Span, extract_source: F) -> Result<String, SpanSnippetError>
         where F: Fn(&str, usize, usize) -> Result<String, SpanSnippetError>
     {
-        if sp.lo() > sp.hi() {
-            return Err(SpanSnippetError::IllFormedSpan(sp));
-        }
-
         let local_begin = self.lookup_byte_offset(sp.lo());
         let local_end = self.lookup_byte_offset(sp.hi());
 
@@ -762,14 +754,14 @@ impl SourceMap {
 
     /// Finds the width of a character, either before or after the provided span.
     fn find_width_of_character_at_span(&self, sp: Span, forwards: bool) -> u32 {
-        // Disregard malformed spans and assume a one-byte wide character.
-        if sp.lo() >= sp.hi() {
-            debug!("find_width_of_character_at_span: early return malformed span");
+        let sp = sp.data();
+        if sp.lo == sp.hi {
+            debug!("find_width_of_character_at_span: early return empty span");
             return 1;
         }
 
-        let local_begin = self.lookup_byte_offset(sp.lo());
-        let local_end = self.lookup_byte_offset(sp.hi());
+        let local_begin = self.lookup_byte_offset(sp.lo);
+        let local_end = self.lookup_byte_offset(sp.hi);
         debug!("find_width_of_character_at_span: local_begin=`{:?}`, local_end=`{:?}`",
                local_begin, local_end);
 

src/libsyntax_pos/lib.rs

@@ -1512,7 +1512,6 @@ pub type FileLinesResult = Result<FileLines, SpanLinesError>;
 
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub enum SpanLinesError {
-    IllFormedSpan(Span),
     DistinctSources(DistinctSources),
 }