Remove an unused StableHash impl.

compiler/rustc_middle/src/ich/impls_syntax.rs

@@ -4,7 +4,7 @@
 use rustc_ast as ast;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hir as hir;
-use rustc_span::{SourceFile, Symbol, sym};
+use rustc_span::{Symbol, sym};
 use smallvec::SmallVec;
 
 use super::StableHashingContext;
@@ -54,56 +54,6 @@ fn is_ignored_attr(name: Symbol) -> bool {
     IGNORED_ATTRIBUTES.contains(&name)
 }
 
-impl<'a> HashStable<StableHashingContext<'a>> for SourceFile {
-    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let SourceFile {
-            name: _, // We hash the smaller stable_id instead of this
-            stable_id,
-            cnum,
-            // Do not hash the source as it is not encoded
-            src: _,
-            ref src_hash,
-            // Already includes src_hash, this is redundant
-            checksum_hash: _,
-            external_src: _,
-            start_pos: _,
-            normalized_source_len: _,
-            unnormalized_source_len: _,
-            lines: _,
-            ref multibyte_chars,
-            ref normalized_pos,
-        } = *self;
-
-        stable_id.hash_stable(hcx, hasher);
-
-        src_hash.hash_stable(hcx, hasher);
-
-        {
-            // We are always in `Lines` form by the time we reach here.
-            assert!(self.lines.read().is_lines());
-            let lines = self.lines();
-            // We only hash the relative position within this source_file
-            lines.len().hash_stable(hcx, hasher);
-            for &line in lines.iter() {
-                line.hash_stable(hcx, hasher);
-            }
-        }
-
-        // We only hash the relative position within this source_file
-        multibyte_chars.len().hash_stable(hcx, hasher);
-        for &char_pos in multibyte_chars.iter() {
-            char_pos.hash_stable(hcx, hasher);
-        }
-
-        normalized_pos.len().hash_stable(hcx, hasher);
-        for &char_pos in normalized_pos.iter() {
-            char_pos.hash_stable(hcx, hasher);
-        }
-
-        cnum.hash_stable(hcx, hasher);
-    }
-}
-
 impl<'tcx> HashStable<StableHashingContext<'tcx>> for rustc_feature::Features {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'tcx>, hasher: &mut StableHasher) {
         // Unfortunately we cannot exhaustively list fields here, since the