Use shorter and more robust l-value and r-value tracking for underscore replacement (#169)

* Use more robust l-value and r-value tracking and add test

* Simplify

* Add tests

* Skip a test on 1.0 because the test itself fails to parse

Author: LilithHafner

src/macro_tools.jl

@@ -1,21 +1,21 @@
 """
-    substitute_underscores(expr, var) -> new, changed
+    substitute_underscores(expr, var, right=false) -> new, changed
 
 Replace all occurrences of `_` in `expr` with `var` and return the new expression and a Bool
 indicating whether the expression was changed.
+
+If `right` is `true`, then expr is in an approximation of r-value position
 """
-substitute_underscores(f::Symbol, var::Symbol) = f === :_ ? (var, true) : (f, false)
-substitute_underscores(f, ::Symbol) = f, false
-function substitute_underscores(ex::Expr, var::Symbol)
+substitute_underscores(ex, var::Symbol) = substitute_underscores(ex, var, true)
+substitute_underscores(s::Symbol, var::Symbol, right) = right && s === :_ ? (var, true) : (s, false)
+substitute_underscores(s, ::Symbol, _) = s, false
+function substitute_underscores(ex::Expr, var::Symbol, right)
     changed = false
     args = similar(ex.args)
-    i = firstindex(args)
-    if ex.head in (:(=), :->, :function)
-        args[i] = ex.args[i]
-        i += 1
-    end
-    for i in i:lastindex(args)
-        args[i], c = substitute_underscores(ex.args[i], var)
+    for i in eachindex(args)
+        force_left = (i == 1 && ex.head in (:(=), :->, :function))
+        force_right = ex.head == :(::) && i == 2 || ex.head in (:ref, :.)
+        args[i], c = substitute_underscores(ex.args[i], var, force_right || right && !force_left)
         changed |= c
     end
     changed ? exprarray(ex.head, args) : ex, changed

test/runtests.jl

@@ -492,6 +492,25 @@ else
         @testset "Issue #156, compat with old constructor" begin
             @test Chairmarks.Sample(0,fill(NaN, 8)...) isa Chairmarks.Sample
         end
+
+        @testset "Issue #167, r-value and l-value detection" begin
+            @b [0] _[1] = 5 seconds=.01
+            @b 1 [0][_] = 5 seconds=.01
+            @b 1 [0][_] seconds=.01
+            @b Int 0::_ seconds=.01
+            @b Int x::_ = 5 seconds=.01
+            @b Int x::_ = 5.0 seconds=.01
+            @test_throws InexactError @b Int x::_ = 5.5
+            @b 1,2 (_, _) = _ seconds=.01
+            @test_throws BoundsError @b 2 (_, _) = _
+            @b 10 for _ in 1:_ rand(10)[_] = 5.0 end seconds=.01
+            @static if VERSION >= v"1.6"
+                mutable struct T167 # Type definition not allowed inside a local scope in Julia 1.0
+                    x::Int
+                end
+                @b T167(5) _.x = 7
+            end
+        end
     end
 
     @testset "Statistics Extension" begin