fix generated_body_to_codeinfo to avoid string (which is not always defined)

Fixes a discrepancy between the code in C before #57230 and in Julia
afterwards, making sure to sequence these definitions correctly. Not
sure how to write a reliable test since it is specific to when this
generated function is defined relative to the helpers used by this
thunk, but the issue/fix is visible with:

```
$ ./julia -e 'code_lowered(ntuple, (Returns{Nothing}, Val{1000000}))'
```

Author: vtjnash

base/Base_compiler.jl

@@ -158,6 +158,31 @@ if false
     println(io::IO, x...) = Core.println(io, x...)
 end
 
+## Load essential files and libraries
+include("essentials.jl")
+
+# Because lowering inserts direct references, it is mandatory for this binding
+# to exist before we start inferring code.
+function string end
+import Core: String
+
+# For OS specific stuff
+# We need to strcat things here, before strings are really defined
+function strcat(x::String, y::String)
+    out = ccall(:jl_alloc_string, Ref{String}, (Int,), Core.sizeof(x) + Core.sizeof(y))
+    gc_x = @_gc_preserve_begin(x)
+    gc_y = @_gc_preserve_begin(y)
+    gc_out = @_gc_preserve_begin(out)
+    out_ptr = unsafe_convert(Ptr{UInt8}, out)
+    unsafe_copyto!(out_ptr, unsafe_convert(Ptr{UInt8}, x), Core.sizeof(x))
+    unsafe_copyto!(out_ptr + Core.sizeof(x), unsafe_convert(Ptr{UInt8}, y), Core.sizeof(y))
+    @_gc_preserve_end(gc_x)
+    @_gc_preserve_end(gc_y)
+    @_gc_preserve_end(gc_out)
+    return out
+end
+
+
 """
     time_ns()::UInt64
 
@@ -172,8 +197,6 @@ const _DOCS_ALIASING_WARNING = """
     Behavior can be unexpected when any mutated argument shares memory with any other argument.
 """
 
-## Load essential files and libraries
-include("essentials.jl")
 include("ctypes.jl")
 include("gcutils.jl")
 include("generator.jl")
@@ -284,7 +307,6 @@ include("rounding.jl")
 include("float.jl")
 
 # Lazy strings
-import Core: String
 include("strings/lazy.jl")
 
 function cld end
@@ -321,22 +343,6 @@ using .Order
 include("coreir.jl")
 include("invalidation.jl")
 
-# Because lowering inserts direct references, it is mandatory for this binding
-# to exist before we start inferring code.
-function string end
-
-# For OS specific stuff
-# We need to strcat things here, before strings are really defined
-function strcat(x::String, y::String)
-    out = ccall(:jl_alloc_string, Ref{String}, (Csize_t,), Core.sizeof(x) + Core.sizeof(y))
-    GC.@preserve x y out begin
-        out_ptr = unsafe_convert(Ptr{UInt8}, out)
-        unsafe_copyto!(out_ptr, unsafe_convert(Ptr{UInt8}, x), Core.sizeof(x))
-        unsafe_copyto!(out_ptr + Core.sizeof(x), unsafe_convert(Ptr{UInt8}, y), Core.sizeof(y))
-    end
-    return out
-end
-
 BUILDROOT::String = ""
 DATAROOT::String = ""
 const DL_LOAD_PATH = String[]

base/essentials.jl

@@ -723,6 +723,8 @@ cconvert(::Type{<:Ptr}, x) = x # but defer the conversion to Ptr to unsafe_conve
 unsafe_convert(::Type{T}, x::T) where {T} = x # unsafe_convert (like convert) defaults to assuming the convert occurred
 unsafe_convert(::Type{T}, x::T) where {T<:Ptr} = x  # to resolve ambiguity with the next method
 unsafe_convert(::Type{P}, x::Ptr) where {P<:Ptr} = convert(P, x)
+unsafe_convert(::Type{Ptr{UInt8}}, s::String) = ccall(:jl_string_ptr, Ptr{UInt8}, (Any,), s)
+unsafe_convert(::Type{Ptr{Int8}}, s::String) = ccall(:jl_string_ptr, Ptr{Int8}, (Any,), s)
 
 """
     reinterpret(::Type{Out}, x::In)

base/expr.jl

@@ -1672,7 +1672,8 @@ function generated_body_to_codeinfo(ex::Expr, defmod::Module, isva::Bool)
     ci = ccall(:jl_expand, Any, (Any, Any), ex, defmod)
     if !isa(ci, CodeInfo)
         if isa(ci, Expr) && ci.head === :error
-            error("syntax: $(ci.args[1])")
+            msg = ci.args[1]
+            error(msg isa String ? strcat("syntax: ", msg) : msg)
         end
         error("The function body AST defined by this @generated function is not pure. This likely means it contains a closure, a comprehension or a generator.")
     end

base/pointer.jl

@@ -59,8 +59,6 @@ cconvert(::Type{Ptr{UInt8}}, s::AbstractString) = String(s)
 cconvert(::Type{Ptr{Int8}}, s::AbstractString) = String(s)
 unsafe_convert(::Type{Ptr{UInt8}}, x::Symbol) = ccall(:jl_symbol_name, Ptr{UInt8}, (Any,), x)
 unsafe_convert(::Type{Ptr{Int8}}, x::Symbol) = ccall(:jl_symbol_name, Ptr{Int8}, (Any,), x)
-unsafe_convert(::Type{Ptr{UInt8}}, s::String) = ccall(:jl_string_ptr, Ptr{UInt8}, (Any,), s)
-unsafe_convert(::Type{Ptr{Int8}}, s::String) = ccall(:jl_string_ptr, Ptr{Int8}, (Any,), s)
 
 cconvert(::Type{<:Ptr}, a::Array) = getfield(a, :ref)
 unsafe_convert(::Type{Ptr{S}}, a::AbstractArray{T}) where {S,T} = convert(Ptr{S}, unsafe_convert(Ptr{T}, a))