Fix to allow named tuple unpacking in let syntax left hand side

Author: c42f

JuliaLowering/src/desugaring.jl

@@ -1843,19 +1843,21 @@ end
 #-------------------------------------------------------------------------------
 # Expand for loops
 
+# Extract the variable names assigned to from a "fancy assignment left hand
+# side" such as nested tuple destructuring.
 function foreach_lhs_var(f::Function, ex)
     k = kind(ex)
     if k == K"Identifier" || k == K"BindingId"
         f(ex)
-    elseif k == K"Placeholder"
-        # Ignored
-    elseif k == K"tuple"
+    elseif k == K"::" && numchildren(ex) == 2
+        foreach_lhs_var(f, ex[1])
+    elseif k == K"tuple" || k == K"parameters"
         for e in children(ex)
             foreach_lhs_var(f, e)
         end
-    else
-        TODO(ex, "LHS vars")
     end
+    # k == K"Placeholder" ignored, along with everything else - we assume
+    # validation is done elsewhere.
 end
 
 function expand_for(ctx, ex)
@@ -1874,7 +1876,6 @@ function expand_for(ctx, ex)
         lhs = iterspec[1]
         if kind(lhs) != K"outer"
             foreach_lhs_var(lhs) do var
-                @chk kind(var) == K"Identifier"
                 push!(copied_vars, @ast ctx var [K"=" var var])
             end
         end

JuliaLowering/test/loops.jl

@@ -45,11 +45,8 @@ let
 end
 """) == [2,4]
 
-# TODO: Test soft scope rules
-
 end
 
-
 @testset "for loops" begin
 
 test_mod = Module()
@@ -144,6 +141,19 @@ let
 end
 """) == 2
 
+# Fancy for loop left hand side - unpacking and scoping
+@test JuliaLowering.include_string(test_mod, """
+let
+    a = []
+    i = 100
+    j = 200
+    for (i,j) in [('a', 'b'), (1,2)]
+        push!(a, (i,j))
+    end
+    (a, i, j)
+end
+""") == ([('a', 'b'), (1,2)], 100, 200)
+
 end
 
 
@@ -162,6 +172,7 @@ end
 """) == [(1,3), (1,4), (2,3), (2,4)]
 
 @testset "break/continue" begin
+
 @test JuliaLowering.include_string(test_mod, """
 let
     a = []
@@ -198,6 +209,8 @@ let
     a
 end
 """) == [(1,2), (1,4), (2,2), (2,4)]
+
+
 end
 
 

JuliaLowering/test/loops_ir.jl

@@ -72,6 +72,47 @@ end
 16  (goto label₇)
 17  (return core.nothing)
 
+########################################
+# Syntax sugar for nested for loop
+for x in xs, y in ys
+    x = 10 # Copy of x; does not overwrite x iteration var
+end
+#---------------------
+1   TestMod.xs
+2   (= slot₂/next (call top.iterate %₁))
+3   slot₂/next
+4   (call core.=== %₃ core.nothing)
+5   (call top.not_int %₄)
+6   (gotoifnot %₅ label₃₄)
+7   slot₂/next
+8   (= slot₃/x (call core.getfield %₇ 1))
+9   (call core.getfield %₇ 2)
+10  TestMod.ys
+11  (= slot₁/next (call top.iterate %₁₀))
+12  slot₁/next
+13  (call core.=== %₁₂ core.nothing)
+14  (call top.not_int %₁₃)
+15  (gotoifnot %₁₄ label₂₈)
+16  slot₃/x
+17  (= slot₄/x %₁₆)
+18  slot₁/next
+19  (= slot₅/y (call core.getfield %₁₈ 1))
+20  (call core.getfield %₁₈ 2)
+21  (= slot₄/x 10)
+22  (= slot₁/next (call top.iterate %₁₀ %₂₀))
+23  slot₁/next
+24  (call core.=== %₂₃ core.nothing)
+25  (call top.not_int %₂₄)
+26  (gotoifnot %₂₅ label₂₈)
+27  (goto label₁₆)
+28  (= slot₂/next (call top.iterate %₁ %₉))
+29  slot₂/next
+30  (call core.=== %₂₉ core.nothing)
+31  (call top.not_int %₃₀)
+32  (gotoifnot %₃₁ label₃₄)
+33  (goto label₇)
+34  (return core.nothing)
+
 ########################################
 # Error: break outside for/while
 break

JuliaLowering/test/scopes_ir.jl

@@ -40,6 +40,16 @@ end
 7   (= slot₃/y (call core.getfield %₆ 1))
 8   (return core.nothing)
 
+########################################
+# let syntax with named tuple on lhs creates locals for the unpacked vars
+let (; x,y) = rhs
+end
+#---------------------
+1   TestMod.rhs
+2   (= slot₁/x (call top.getproperty %₁ :x))
+3   (= slot₂/y (call top.getproperty %₁ :y))
+4   (return core.nothing)
+
 ########################################
 # Let syntax with the same name creates nested bindings
 let x = f(x), x = g(x)