Fix diagnostics covering trailing text

Diagnostics may sometimes cover trailing text which wasn't consumed. For example,
`parseatom(")")` doesn't consume the errant trailing ')', but the
diagnostic refers to this character. In this case, `SourceFile` needs to
cover the location of the diagnostic in addition to any text which is
consumed.

As part of this, mark `sourcetext(::ParseStream)` as deprecated, in
favour of constructing a `SourceFile` to wrap things up more neatly.

Also fix a bug in `highlight()` for empty `SourceFile`s.

src/parse_stream.jl

@@ -331,7 +331,7 @@ function Base.show(io::IO, mime::MIME"text/plain", stream::ParseStream)
 end
 
 function show_diagnostics(io::IO, stream::ParseStream)
-    show_diagnostics(io, stream.diagnostics, sourcetext(stream))
+    show_diagnostics(io, stream.diagnostics, SourceFile(stream))
 end
 
 # We manage a pool of stream positions as parser working space
@@ -1078,17 +1078,8 @@ function build_tree(make_node::Function, ::Type{NodeType}, stream::ParseStream;
     end
 end
 
-"""
-    sourcetext(stream::ParseStream; steal_textbuf=true)
-
-Return the source text being parsed by this `ParseStream` as a UTF-8 encoded
-string.
-
-If `steal_textbuf==true`, this is permitted to steal the content of the
-stream's text buffer. Note that this leaves the `ParseStream` in an invalid
-state for further parsing.
-"""
 function sourcetext(stream::ParseStream; steal_textbuf=false)
+    Base.depwarn("Use of `sourcetext(::ParseStream)` is deprecated. Use `SourceFile(stream)` instead", :sourcetext)
     root = stream.text_root
     # The following kinda works but makes the return type of this method type
     # unstable. (Also codeunit(root) == UInt8 doesn't imply UTF-8 encoding?)
@@ -1109,7 +1100,19 @@ function sourcetext(stream::ParseStream; steal_textbuf=false)
 end
 
 function SourceFile(stream::ParseStream; kws...)
-    return SourceFile(sourcetext(stream); first_index=first_byte(stream), kws...)
+    fbyte = first_byte(stream)
+    lbyte = maximum((last_byte(d) for d in stream.diagnostics);
+                    init=last_byte(stream))
+    # See also sourcetext()
+    srcroot = stream.text_root
+    str = if srcroot isa String
+        SubString(srcroot, fbyte, thisind(srcroot, lbyte))
+    elseif srcroot isa SubString{String}
+        SubString(srcroot, fbyte, thisind(srcroot, lbyte))
+    else
+        SubString(String(stream.textbuf[fbyte:lbyte]))
+    end
+    return SourceFile(str; first_index=first_byte(stream), kws...)
 end
 
 """

src/parser.jl

@@ -3561,7 +3561,8 @@ function parse_atom(ps::ParseState, check_identifiers=true)
         msg = leading_kind == K"EndMarker" ?
               "premature end of input" :
               "unexpected `$(untokenize(leading_kind))`"
-        bump_invisible(ps, K"error", error=msg)
+        emit_diagnostic(ps, error=msg)
+        bump_invisible(ps, K"error")
     else
         bump(ps, error="invalid syntax atom")
     end

src/source_files.jl

@@ -219,7 +219,9 @@ function highlight(io::IO, source::SourceFile, range::UnitRange;
         print(io, source[x:p-1])
         _printstyled(io, hitext; bgcolor=color)
         print(io, source[q+1:d])
-        source[thisind(source, d)] == '\n' || print(io, "\n")
+        if d >= firstindex(source) && source[thisind(source, d)] != '\n'
+            print(io, "\n")
+        end
         _print_marker_line(io, source[a:p-1], hitext, true, true, marker_line_color, note, notecolor)
     else
         # x   --------------

test/diagnostics.jl

@@ -1,6 +1,6 @@
-function diagnostic(str; only_first=false, allow_multiple=false)
+function diagnostic(str; only_first=false, allow_multiple=false, rule=:all)
     stream = ParseStream(str)
-    parse!(stream)
+    parse!(stream, rule=rule)
     if allow_multiple
         stream.diagnostics
     else
@@ -52,7 +52,11 @@ end
         Diagnostic(6, 5, :error, "invalid macro name")
 
 	@test diagnostic("a, , b") ==
-        Diagnostic(4, 3, :error, "unexpected `,`")
+        Diagnostic(4, 4, :error, "unexpected `,`")
+    @test diagnostic(")", allow_multiple=true) == [
+        Diagnostic(1, 1, :error, "unexpected `)`")
+        Diagnostic(1, 1, :error, "extra tokens after end of expression")
+    ]
 
     @test diagnostic("if\nfalse\nend") ==
         Diagnostic(3, 3, :error, "missing condition in `if`")
@@ -99,6 +103,11 @@ end
 
     @test diagnostic("\"\$(x,y)\"") ==
         Diagnostic(3, 7, :error, "invalid interpolation syntax")
+
+    @test diagnostic("", rule=:statement) ==
+        Diagnostic(1, 0, :error, "premature end of input")
+    @test diagnostic("", rule=:atom) ==
+        Diagnostic(1, 0, :error, "premature end of input")
 end
 
 @testset "parser warnings" begin

test/source_files.jl

@@ -115,6 +115,9 @@ end
     @test sprint(highlight, SourceFile("a\nα"), 1:4) == "┌\na\nα\n┘"
     @test sprint(highlight, SourceFile("a\nb\nα"), 3:3) == "a\nb\n╙\nα"
 
+    # empty files
+    @test sprint(highlight, SourceFile(""), 1:0) == "└"
+
     # Multi-line ranges
     @test sprint(highlight, src, 1:7) == """
         ┌───