Implement __LINE__ magic macros

Fixes JuliaLang#8066

NEWS.md

@@ -58,6 +58,7 @@ New language features
  Default continues to be of length 1 ([#12385]).
  See http:https://docs.julialang.org/en/latest/manual/parallel-computing/#remoterefs-and-abstractchannels for details.
 
+ * `@__LINE__` special macro now available to reflect invocation source line number ([#12727]).
 
 Language changes
 ----------------

base/docs/helpdb.jl

@@ -2,6 +2,8 @@
 
 # Base.LinAlg.BLAS
 
+import .Docs: keywords
+
 doc"""
  ger!(alpha, x, y, A)
 
@@ -9537,12 +9539,20 @@ Returns an iterator over substrings of `s` that correspond to the extended graph
 """
 graphemes
 
-doc"""
+keywords[symbol("@__FILE__")] = doc"""
+
  @__FILE__() -> AbstractString
 
-`@__FILE__` expands to a string with the absolute path and file name of the script being run. Returns `nothing` if run from a REPL or an empty string if evaluated by `julia -e <expr>`.
+`@__FILE__` expands to a string with the absolute path and file name of the script being run.
+Returns `"none"` if run from a REPL or command-line context.
+"""
+
+keywords[symbol("@__LINE__")] = doc"""
+
+ @__LINE__() -> Int
+
+`@__LINE__` expands to the line number of the call-site.
 """
-:@__FILE__
 
 doc"""
  charwidth(c)

src/julia-parser.scm

@@ -2039,14 +2039,17 @@
  (with-space-sensitive
  (let* ((head (parse-unary-prefix s))
  (t (peek-token s)))
- (if (ts:space? s)
+ (cond
+ ((eqv? head '__LINE__) (input-port-line (ts:port s)))
+ ((ts:space? s)
  `(macrocall ,(macroify-name head)
- ,@(parse-space-separated-exprs s))
- (let ((call (parse-call-chain s head #t)))
- (if (and (pair? call) (eq? (car call) 'call))
+ ,@(parse-space-separated-exprs s)))
+ (else
+ (let ((call (parse-call-chain s head #t)))
+ (if (and (pair? call) (eq? (car call) 'call))
  `(macrocall ,(macroify-name (cadr call)) ,@(cddr call))
  `(macrocall ,(macroify-name call)
- ,@(parse-space-separated-exprs s))))))))
+ ,@(parse-space-separated-exprs s)))))))))
 
  ;; command syntax
  ((eqv? t #\`)

test/loading.jl

@@ -2,6 +2,8 @@
 
 using Base.Test
 
+@test @__LINE__ == 5
+
 include("test_sourcepath.jl")
 thefname = "the fname!//\\&\0\1*"
 @test include_string("include_string_test() = @__FILE__", thefname)() == Base.source_path()