Make @__DIR__ return pwd() when being run without a file (#21759)

NEWS.md

@@ -17,6 +17,10 @@ This section lists changes that do not have deprecation warnings.
   * `ntuple(f, n::Integer)` throws `ArgumentError` if `n` is negative.
     Previously an empty tuple was returned ([#21697]).
 
+  * `@__DIR__` returns the current working directory rather than `nothing` when not run
+    from a file ([#21759]).
+
+
 Library improvements
 --------------------
 

base/loading.jl

@@ -529,7 +529,7 @@ end
 
 function source_dir()
     p = source_path(nothing)
-    p === nothing ? p : dirname(p)
+    p === nothing ? pwd() : dirname(p)
 end
 
 """
@@ -545,7 +545,7 @@ macro __FILE__() source_path() end
     @__DIR__ -> AbstractString
 
 `@__DIR__` expands to a string with the directory part of the absolute path of the file
-containing the macro. Returns `nothing` if run from a REPL or an empty string if
+containing the macro. Returns the current working directory if run from a REPL or if
 evaluated by `julia -e <expr>`.
 """
 macro __DIR__() source_dir() end

test/loading.jl

@@ -14,6 +14,12 @@ include_string_test_func = include_string("include_string_test() = @__FILE__", t
 
 @test isdir(@__DIR__)
 @test @__DIR__() == dirname(@__FILE__)
+let exename = `$(Base.julia_cmd()) --precompiled=yes --startup-file=no`
+    wd = sprint(show, pwd())
+    @test readchomp(`$exename -E "@__DIR__" -i`) == wd
+    @test readchomp(`$exename -E "cd(()->eval(:(@__DIR__)), tempdir())" -i`) != wd
+    @test readchomp(`$exename -E "@__DIR__"`) == wd # non-interactive
+end
 
 # Issue #5789 and PR #13542:
 mktempdir() do dir