add ability to evaluate ssavalues and locals (#395)

* add ability to evaluate ssavalues and locals

* fix for 1.0

* add some docs

src/utils.jl

@@ -493,6 +493,9 @@ julia> JuliaInterpreter.locals(frame)
  #self# = capture
  x = Core.Box(2)
 ```
+
+"Special" values like SSA values and slots (shown in lowered code as e.g. `%3` and `@_4`
+respectively) can be evaluated using the syntax `var"%3"` and `var"@_4"` respectively.
 """
 function eval_code end
 
@@ -508,9 +511,13 @@ function eval_code(frame::Frame, expr)
     end
     # see https://github.com/JuliaLang/julia/issues/31255 for the Symbol("") check
     vars = filter(v -> v.name != Symbol(""), locals(frame))
+    defined_ssa = findall(x -> x!=0, [isassigned(data.ssavalues, i) for i in 1:length(data.ssavalues)])
+    defined_locals = findall(x -> x isa Some, data.locals)
     res = gensym()
     eval_expr = Expr(:let,
-        Expr(:block, map(x->Expr(:(=), x...), [(v.name, maybe_quote(v.value isa Core.Box ? v.value.contents : v.value)) for v in vars])...),
+                     Expr(:block, map(x->Expr(:(=), x...), [(v.name, maybe_quote(v.value isa Core.Box ? v.value.contents : v.value)) for v in vars])...,
+                     map(x->Expr(:(=), x...), [(Symbol("%$i"), data.ssavalues[i]) for i in defined_ssa])...,
+                     map(x->Expr(:(=), x...), [(Symbol("@_$i"), data.locals[i].value) for i in defined_locals])...),
         Expr(:block,
             Expr(:(=), res, expr),
             Expr(:tuple, res, Expr(:tuple, [v.name for v in vars]...))

test/eval_code.jl

@@ -73,3 +73,14 @@ fr, bp = debug_command(fr, :c)
 @test eval_code(fr, "garbage") == ones(10)
 eval_code(fr, "non_accessible_variable = 5.0")
 @test eval_code(fr, "non_accessible_variable") == 5.0
+
+if VERSION >= v"1.4" # for var"" syntax
+    # Evaluating SSAValues
+    f(x) = x^2
+    frame = JuliaInterpreter.enter_call(f, 5)
+    JuliaInterpreter.step_expr!(frame)
+    JuliaInterpreter.step_expr!(frame)
+    # This could change with changes to Julia lowering
+    @test eval_code(frame, "var\"%2\"") == Val(2)
+    @test eval_code(frame, "var\"@_1\"") == f
+end