Support K"gc_preserve"

Note that this lowering may change in JuliaLang/julia#59129

Author: mlechu

src/desugaring.jl

@@ -4537,6 +4537,15 @@ function expand_forms_2(ctx::DesugaringContext, ex::SyntaxTree, docs=nothing)
         ]
     elseif k == K"inert"
         ex
+    elseif k == K"gc_preserve"
+        s = ssavar(ctx, ex)
+        r = ssavar(ctx, ex)
+        @ast ctx ex [K"block"
+            [K"=" s [K"gc_preserve_begin" children(ex)[2:end]...]]
+            [K"=" r expand_forms_2(ctx, children(ex)[1])]
+            [K"gc_preserve_end" s]
+            r
+        ]
     elseif k == K"&"
         throw(LoweringError(ex, "invalid syntax"))
     elseif k == K"$"

src/kinds.jl

@@ -11,6 +11,7 @@ function _register_kinds()
             # Flag for @generated parts of a functon
             "generated"
             # Temporary rooting of identifiers (GC.@preserve)
+            "gc_preserve"
             "gc_preserve_begin"
             "gc_preserve_end"
             # A literal Julia value of any kind, as might be inserted into the

test/macros.jl

@@ -310,4 +310,13 @@ end
     MethodError: no method matching var"@sig_mismatch"(::JuliaLowering.MacroContext, ::JuliaLowering.SyntaxTree""")
 end
 
+@testset "old macros producing exotic expr heads" begin
+    @test JuliaLowering.include_string(test_mod, """
+    let # example from @preserve docstring
+        x = Ref{Int}(101)
+        p = Base.unsafe_convert(Ptr{Int}, x)
+        GC.@preserve x unsafe_load(p)
+     end""") === 101 # Expr(:gc_preserve)
+end
+
 end # module macros