Add the @public macro

.gitignore

@@ -0,0 +1 @@
+Manifest.toml

Project.toml

@@ -2,3 +2,13 @@ name = "Public"
 uuid = "431bcebd-1456-4ced-9d72-93c2757fff0b"
 authors = ["The Julia Project", "contributors"]
 version = "1.0.0-DEV"
+
+[compat]
+Test = "<0.0.1, 1"
+julia = "1"
+
+[extras]
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[targets]
+test = ["Test"]

README.md

@@ -0,0 +1,21 @@
+# Public.jl
+
+## Example usage
+
+```julia
+module HelloWorld
+
+using Public: @public
+
+@public f
+
+function f()
+    return "hello"
+end
+
+function g()
+    return "world"
+end
+
+end # module
+```

src/Public.jl

@@ -0,0 +1,82 @@
+module Public
+
+# Based on Compat.jl
+# License: MIT
+# https://github.com/JuliaLang/Compat.jl
+# https://github.com/JuliaLang/Compat.jl/blob/master/src/compatmacro.jl
+# https://github.com/JuliaLang/Compat.jl/blob/a62d95906f3c16c9fa0fe8369a6613dcfd2a4659/src/compatmacro.jl
+
+# https://github.com/JuliaLang/julia/pull/50105
+@static if Base.VERSION >= v"1.11.0-DEV.469"
+    macro public(symbols_expr::Union{Symbol, Expr})
+        symbols = _get_symbols(symbols_expr)
+        return esc(Expr(:public, symbols...))
+    end
+else
+    macro public(symbols_expr::Union{Symbol, Expr})
+        return nothing
+    end
+end
+
+_get_symbols(sym::Symbol) = [sym]
+
+function _get_symbols(expr::Expr)
+    # `expr` must either be a "valid macro expression" or a tuple expression.
+
+    # If `expr` is a "valid macro expression", then we simply return it:
+    if _is_valid_macro_expr(expr::Expr)
+        return [expr.args[1]]
+    end
+
+    # If `expr` is not a "valid macro expression", then we check to make sure
+    # that it is a tuple expression:
+    if expr.head != :tuple
+        msg = """
+            Invalid expression head `$(expr.head)` in expression `$(expr)`.
+            Try `@public foo, bar, @hello, @world`
+        """
+        throw(ArgumentError(msg))
+    end
+
+    # Now that we know that `expr` is a tuple expression, we iterate over
+    # each element of the tuple
+    num_symbols = length(expr.args)
+    symbols = Vector{Symbol}(undef, num_symbols)
+    for (i, arg) in enumerate(expr.args)
+    end
+    return symbols
+end
+
+# Return true if and only if `expr` is a valid macro call with no arguments.
+#
+# Example of "good" input: `@foo`
+function _is_valid_macro_expr(expr::Expr)
+    # `expr` must be a `:macrocall` expression:
+    Meta.isexpr(expr, :macrocall) || return false
+
+    # `expr` must have exactly two arguments:
+    (length(expr.args) == 2) || return false
+
+    # The first argument must be a Symbol:
+    (expr.args[1] isa Symbol) || return false
+
+    # The first argument must begin with `@`
+    arg1_str = string(expr.args[1])
+    (arg1_str[1] == '@') || return false
+
+    # The first argument must have length >= 2
+    # (because otherwise the first argument would just be `@`, which doesn't
+    # make sense)
+    (length(arg1_str) >= 2) || return false
+
+    # The second argument must be a `LineNumberNode`
+    (expr.args[2] isa LineNumberNode) || return false
+
+    return true
+end
+
+# TODO: figure out if we actually want to `export`,
+# or if we just want to mark as public.
+export @public
+
+end # module Public

test/runtests.jl

@@ -0,0 +1,55 @@
+import Public
+import Test
+
+using Test: @testset
+using Test: @test
+
+@testset "Public.jl package" begin
+    @testset "_is_valid_macro_expr" begin
+        good_exprs = [
+            :(@hello),
+            Meta.parse("@hello"),
+        ]
+        bad_exprs = [
+            Meta.parse("@foo bar"),
+            Meta.parse("@foo(bar)"),
+        ]
+        for expr in good_exprs
+            @testset let context = (; expr)
+                @test Public._is_valid_macro_expr(expr)
+            end
+
+        end
+        for expr in bad_exprs
+            @testset let context = (; expr)
+                @test !Public._is_valid_macro_expr(expr)
+            end
+        end
+    end
+end
+
+module TestModule1
+
+using Public: @public
+
+export f
+@public g
+
+function f end
+function g end
+function h end
+
+end # module TestModule1
+
+@test Base.isexported(TestModule1, :f)
+@test !Base.isexported(TestModule1, :g)
+@test !Base.isexported(TestModule1, :h)
+
+# @test Base.ispublic(TestModule1, :f)
+# @test !Base.ispublic(TestModule1, :h)
+
+@static if Base.VERSION >= v"1.11.0-DEV.469"
+    # @test Base.ispublic(TestModule1, :g)
+else
+    # @test !Base.ispublic(TestModule1, :g)
+end