add @locals macro for obtaining dictionary of local vars and values

NEWS.md

@@ -5,6 +5,8 @@ New language features
 ---------------------
 
   * An *exception stack* is maintained on each task to make exception handling more robust and enable root cause analysis using `catch_stack` ([#28878]).
+  * The experimental macro `Base.@locals` returns a dictionary of current local variable names
+    and values ([#29733]).
 
 Language changes
 ----------------

base/reflection.jl

@@ -250,6 +250,42 @@ macro isdefined(s::Symbol)
     return Expr(:isdefined, esc(s))
 end
 
+"""
+    @locals()
+
+Construct a dictionary of the names (as symbols) and values of all local
+variables defined as of the call site.
+
+# Examples
+```jldoctest
+julia> let x = 1, y = 2
+           Base.@locals
+       end
+Dict{Symbol,Any} with 2 entries:
+  :y => 2
+  :x => 1
+
+julia> function f(x)
+           local y
+           show(Base.@locals); println()
+           for i = 1:1
+               show(Base.@locals); println()
+           end
+           y = 2
+           show(Base.@locals); println()
+           nothing
+       end;
+
+julia> f(42)
+Dict{Symbol,Any}(:x=>42)
+Dict{Symbol,Any}(:i=>1,:x=>42)
+Dict{Symbol,Any}(:y=>2,:x=>42)
+```
+"""
+macro locals()
+    return Expr(:locals)
+end
+
 """
     objectid(x)
 

src/julia-syntax.scm

@@ -2442,6 +2442,27 @@
          (if (not (memq (cadr e) env))
              (error "no outer local variable declaration exists for \"for outer\""))
          '(null))
+        ((eq? (car e) 'locals)
+         (let* ((names (filter (lambda (v)
+                                 (and (not (gensym? v))
+                                      (not (length= (string-split (string v) "#") 2))
+                                      (let ((r (assq v renames)))
+                                        (or (atom? r)
+                                            (let ((mapping (cdr r)))
+                                              (not (and (pair? mapping)
+                                                        (eq? (car mapping) 'outerref))))))))
+                               env))
+                (names (delete-duplicates
+                        (filter (lambda (v) (not (eq? v '||)))
+                                (map unmangled-name names))))
+                (d (make-ssavalue)))
+           `(block (= ,d (call (call (core apply_type) (top Dict) (core Symbol) (core Any))))
+                   ,@(map (lambda (v)
+                            (let ((var (resolve-scopes- v env implicitglobals lam renames newlam sp)))
+                              `(if (isdefined ,var)
+                                   (call (top setindex!) ,d ,var (quote ,v)))))
+                          names)
+                   ,d)))
         ((eq? (car e) 'lambda)
          (let* ((lv   (lam:vars e))
                 (env  (append lv env))
@@ -2494,6 +2515,7 @@
                 (new-renames (append (map cons need-rename renamed) ;; map from definition name -> gensym name
                                      (map cons need-rename-def renamed-def)
                                      (map (lambda (g) (cons g `(outerref ,g))) new-iglo)
+                                     (map (lambda (g) (cons g `(outerref ,g))) glob)
                                      (filter (lambda (ren) ;; old renames list, with anything in vars removed
                                                (let ((var (car ren)))
                                                  (not (or (memq var all-vars) ;; remove anything new

test/reflection.jl

@@ -813,3 +813,36 @@ f20872(::Val, ::Val) = false
 module M29962 end
 # make sure checking if a binding is deprecated does not resolve it
 @test !Base.isdeprecated(M29962, :sin) && !Base.isbindingresolved(M29962, :sin)
+
+# @locals
+using Base: @locals
+let
+    local x, y
+    global z
+    @test isempty(keys(@locals))
+    x = 1
+    @test @locals() == Dict{Symbol,Any}(:x=>1)
+    y = ""
+    @test @locals() == Dict{Symbol,Any}(:x=>1,:y=>"")
+    for i = 8:8
+        @test @locals() == Dict{Symbol,Any}(:x=>1,:y=>"",:i=>8)
+    end
+    for i = 42:42
+        local x
+        @test @locals() == Dict{Symbol,Any}(:y=>"",:i=>42)
+    end
+    @test @locals() == Dict{Symbol,Any}(:x=>1,:y=>"")
+    x = (y,)
+    @test @locals() == Dict{Symbol,Any}(:x=>("",),:y=>"")
+end
+
+function _test_at_locals1(::Any, ::Any)
+    x = 1
+    @test @locals() == Dict{Symbol,Any}(:x=>1)
+end
+_test_at_locals1(1,1)
+function _test_at_locals2(a::Any, ::Any)
+    x = 2
+    @test @locals() == Dict{Symbol,Any}(:x=>2,:a=>a)
+end
+_test_at_locals2(1,1)