Make trivial interpolations like :($x) work

Perhaps surprisingly this is a special case because there's no enclosing
expression.

src/macro_expansion.jl

@@ -25,6 +25,9 @@ end
 # Expansion of quoted expressions
 function collect_unquoted!(ctx, unquoted, ex, depth)
     if kind(ex) == K"$" && depth == 0
+        # children(ex) is usually length 1, but for double interpolation it may
+        # be longer and the children may contain K"..." expressions. Wrapping
+        # in a tuple groups the arguments together correctly in those cases.
         push!(unquoted, @ast ctx ex [K"tuple" children(ex)...])
     else
         inner_depth = kind(ex) == K"quote" ? depth + 1 :

src/runtime.jl

@@ -62,9 +62,6 @@ function _interpolate_ast(ctx::InterpolationContext, ex, depth)
 end
 
 function interpolate_ast(ex, values...)
-    if kind(ex) == K"$"
-        TODO(ex, "\$ in interpolate_ast")
-    end
     # Construct graph for interpolation context. We inherit this from the macro
     # context where possible by detecting it using __macro_ctx__. This feels
     # hacky though.
@@ -88,7 +85,17 @@ function interpolate_ast(ex, values...)
     # We must copy the AST into our context to use it as the source reference
     # of generated expressions.
     ex1 = copy_ast(ctx, ex)
-    _interpolate_ast(ctx, ex1, 0)
+    if kind(ex1) == K"$"
+        @assert length(values) == 1
+        vs = values[1]
+        if length(vs) > 1
+            # :($($(xs...))) where xs is more than length 1
+            throw(LoweringError(ex1, "More than one value in bare `\$` expression"))
+        end
+        _interpolated_value(ctx, ex1, only(vs))
+    else
+        _interpolate_ast(ctx, ex1, 0)
+    end
 end
 
 # Construct new bare module including only the "default names"

test/demo.jl

@@ -260,7 +260,11 @@ src = """
 """
 
 src = """
-x = :hi
+begin
+    a = 1
+    xs = [:(a),]
+    x = :(:(\$(\$(xs...))))
+end
 """
 
 ex = parsestmt(SyntaxTree, src, filename="foo.jl")

test/loops.jl

@@ -45,11 +45,11 @@ let
 end
 """) == [2,4]
 
-@test_throws JuliaLowering.LoweringError JuliaLowering.include_string(test_mod, """
+@test_throws LoweringError JuliaLowering.include_string(test_mod, """
 break
 """)
 
-@test_throws JuliaLowering.LoweringError JuliaLowering.include_string(test_mod, """
+@test_throws LoweringError JuliaLowering.include_string(test_mod, """
 continue
 """)
 

test/quoting.jl

@@ -57,6 +57,16 @@ let
 end
 """))
 
+# Test that trivial interpolation without any nesting works.
+ex = JuliaLowering.include_string(test_mod, """
+let
+    x = 123
+    :(\$x)
+end
+""")
+@test kind(ex) == K"Value"
+@test ex.value == 123
+
 # interpolations at multiple depths
 ex = JuliaLowering.include_string(test_mod, """
 let
@@ -102,4 +112,24 @@ ex2 = JuliaLowering.eval(test_mod, ex)
 @test JuliaLowering.include_string(test_mod, ":x") isa Symbol
 @test JuliaLowering.include_string(test_mod, ":(x)") isa SyntaxTree
 
+# Double interpolation
+ex = JuliaLowering.include_string(test_mod, """
+let
+    args = (:(xxx),)
+    :(:(\$\$(args...)))
+end
+""")
+Base.eval(test_mod, :(xxx = 111))
+ex2 = JuliaLowering.eval(test_mod, ex)
+@test kind(ex2) == K"Value"
+@test ex2.value == 111
+
+double_interp_ex = JuliaLowering.include_string(test_mod, """
+let
+    args = (:(x), :(y))
+    :(:(\$\$(args...)))
+end
+""")
+@test_throws LoweringError JuliaLowering.eval(test_mod, double_interp_ex)
+
 end

test/runtests.jl

@@ -292,12 +292,12 @@ end == [
 ]
 
 
-@test_throws JuliaLowering.LoweringError JuliaLowering.include_string(test_mod, """
+@test_throws LoweringError JuliaLowering.include_string(test_mod, """
 macro mmm(a; b=2)
 end
 """)
 
-@test_throws JuliaLowering.LoweringError JuliaLowering.include_string(test_mod, """
+@test_throws LoweringError JuliaLowering.include_string(test_mod, """
 macro A.b(ex)
 end
 """)

test/utils.jl

@@ -10,7 +10,7 @@ using JuliaLowering:
     Kind, SourceRef, SyntaxTree, NodeId,
     makenode, makeleaf, setattr!, sethead!,
     haschildren, numchildren, children,
-    @ast, flattened_provenance, showprov
+    @ast, flattened_provenance, showprov, LoweringError
 
 function _ast_test_graph()
     graph = SyntaxGraph()