var"str" string macro for unparsable identifiers

NEWS.md

@@ -25,6 +25,7 @@ New library functions
 * `findfirst`, `findlast`, `findnext` and `findprev` now accept a character as first argument
   to search for that character in a string passed as the second argument ([#31664]).
 * New `findall(pattern, string)` method where `pattern` is a string or regex ([#31834]).
+* The `@var_str` string macro can create variable names which won't parse as normal julia syntax ([#32408]).
 
 Standard library changes
 ------------------------

base/exports.jl

@@ -959,6 +959,7 @@ export
     @gensym,
     @eval,
     @deprecate,
+    @var_str,
 
     # performance annotations
     @boundscheck,

base/expr.jl

@@ -427,3 +427,24 @@ macro generated(f)
         error("invalid syntax; @generated must be used with a function definition")
     end
 end
+
+"""
+    @var_str(str) -> Symbol
+
+Refer to a variable named `Symbol(str)`, even when `str` is not a valid name
+in normal Julia source code.
+
+This can help interoperability with programming languages which have different
+rules for the construction of valid identifiers. For example, to refer to the
+`R` variable `draw.segments`, you can use `var"draw.segments"` in your Julia
+code.
+
+`@var_str` is also used to `show` julia source code which has been macro
+expanded or otherwise contains variable names which can't be parsed normally.
+
+!!! compat "Julia 1.3"
+    This macro requires at least Julia 1.3.
+"""
+macro var_str(str)
+    esc(Symbol(str))
+end

doc/src/base/base.md

@@ -251,6 +251,7 @@ Base.@nospecialize
 Base.@specialize
 Base.gensym
 Base.@gensym
+Base.@var_str
 Base.@goto
 Base.@label
 Base.@simd

test/choosetests.jl

@@ -54,7 +54,7 @@ function choosetests(choices = [])
         "checked", "bitset", "floatfuncs", "precompile",
         "boundscheck", "error", "ambiguous", "cartesian", "osutils",
         "channels", "iostream", "secretbuffer", "specificity",
-        "reinterpretarray", "syntax", "logging", "missing", "asyncmap"
+        "reinterpretarray", "syntax", "logging", "missing", "asyncmap", "expr"
     ]
 
     tests = []

test/expr.jl

@@ -0,0 +1,5 @@
+@testset "var_str" begin
+    @test macroexpand(@__MODULE__, :(var"@foo")) == Symbol("@foo")
+    @test macroexpand(@__MODULE__, :(var"##")) == Symbol("##")
+    @test macroexpand(@__MODULE__, :(var"a-b")) == Symbol("a-b")
+end