From 3de7e152d7b6e62b8b2063287c90f76f0f348cdd Mon Sep 17 00:00:00 2001
From: Cody Tapscott <topolarity@tapscott.me>
Date: Tue, 3 Jun 2025 15:49:47 -0400
Subject: [PATCH] static_show: Print `primitive` types with
 `Base.reinterpret(...)`

---
 src/rtutils.c | 20 ++++++++++++++++++--
 test/show.jl  |  7 +++++--
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/src/rtutils.c b/src/rtutils.c
index e3672ab5d887e..41342e2f2ce2d 100644
--- a/src/rtutils.c
+++ b/src/rtutils.c
@@ -1348,8 +1348,18 @@ static size_t jl_static_show_x_(JL_STREAM *out, jl_value_t *v, jl_datatype_t *vt
         // typeof(v) isa DataType, so v is an *instance of* a type that is a Datatype,
         // meaning v is e.g. an instance of a struct. These are printed as a call to a
         // type constructor, such as e.g. `Base.UnitRange{Int64}(start=1, stop=2)`
+
         int istuple = jl_is_tuple_type(vt), isnamedtuple = jl_is_namedtuple_type(vt);
+        int isprimitivetype = jl_is_primitivetype(vt);
+
+        // In many cases, default constructors may not be available (e.g. primitive types
+        // never have them), so print these as "reinterpret(Foo, ...)" to make sure that
+        // these round-trip as expected.
+        int reinterpret = isprimitivetype;
+
         size_t tlen = jl_datatype_nfields(vt);
+        if (reinterpret)
+            n += jl_printf(out, "Base.reinterpret(");
         if (isnamedtuple) {
             if (tlen == 0)
                 n += jl_printf(out, "NamedTuple");
@@ -1357,7 +1367,10 @@ static size_t jl_static_show_x_(JL_STREAM *out, jl_value_t *v, jl_datatype_t *vt
         else if (!istuple) {
             n += jl_static_show_x(out, (jl_value_t*)vt, depth, ctx);
         }
-        n += jl_printf(out, "(");
+        if (reinterpret)
+            n += jl_printf(out, ", ");
+        if (!isprimitivetype)
+            n += jl_printf(out, "(");
         size_t nb = jl_datatype_size(vt);
         if (nb > 0 && tlen == 0) {
             uint8_t *data = (uint8_t*)v;
@@ -1405,7 +1418,10 @@ static size_t jl_static_show_x_(JL_STREAM *out, jl_value_t *v, jl_datatype_t *vt
                 n += jl_static_show_next_(out, next, v, depth, ctx);
             }
         }
-        n += jl_printf(out, ")");
+        if (!isprimitivetype)
+            n += jl_printf(out, ")");
+        if (reinterpret)
+            n += jl_printf(out, ")");
     }
     else {
         n += jl_printf(out, "<?#%p::", (void*)v);
diff --git a/test/show.jl b/test/show.jl
index 8abd99cf95455..6a1b6fdc12624 100644
--- a/test/show.jl
+++ b/test/show.jl
@@ -1520,7 +1520,7 @@ function static_shown(x)
 end
 
 # Test for PR 17803
-@test static_shown(Int128(-1)) == "Int128(0xffffffffffffffffffffffffffffffff)"
+@test static_shown(Int128(-1)) == "Base.reinterpret(Int128, 0xffffffffffffffffffffffffffffffff)"
 
 # PR #22160
 @test static_shown(:aa) == ":aa"
@@ -1618,9 +1618,12 @@ struct var"%X%" end  # Invalid name without '#'
             Val(1),       Val(Int8(1)),  Val(Int16(1)),  Val(Int32(1)),  Val(Int64(1)),  Val(Int128(1)),
             Val(UInt(1)), Val(UInt8(1)), Val(UInt16(1)), Val(UInt32(1)), Val(UInt64(1)), Val(UInt128(1)),
 
+            # Primitive types should round-trip via reinterpret(...)
+            Val(Char('u')), Val(Char('\0')),
+
             # BROKEN
             # Symbol("a\xffb"),
-            # User-defined primitive types
+            # User-defined primitive types with size not a power-of-two
             # Non-canonical NaNs
             # BFloat16
         )