Switch noshift substring constructor to unsafe_substring

Author: jakobnissen

src/JuliaSyntaxHighlighting.jl

@@ -460,8 +460,19 @@ function highlight!(str::AnnotatedString; syntax_errors::Bool = false)
     str
 end
 
+# The undocumented :noshift constructor was removed between Julia 1.12 and Julia 1.13.
+@static if isdefined(Base, :unsafe_substring)
+    function plain_string(s::SubString{<:AnnotatedString})
+        @inbounds Base.unsafe_substring(s.string, s.offset + 1, s.ncodeunits)
+    end
+else
+    function plain_string(s::SubString{AnnotatedString{S}}) where S
+        SubString{S}(s.string.string, s.offset, s.ncodeunits, Val(:noshift))
+    end
+end
+
 function highlight!(str::SubString{AnnotatedString{S}}; syntax_errors::Bool = false) where {S}
-    plainstr = SubString{S}(str.string.string, str.offset, str.ncodeunits, Val(:noshift))
+    plainstr = plain_string(str)
     for ann in _hl_annotations(plainstr, parseall(GreenNode, plainstr, ignore_errors=true); syntax_errors)
         annotate!(str, ann.region, ann.label, ann.value)
     end