[core] codegen: Implement construction of unsized ndarrays

Partially based on f731e604: core/ndstrides: add more ScalarOrNDArray
and NDArrayObject utils.

nac3core/src/codegen/types/ndarray/mod.rs

@@ -1,7 +1,7 @@
 use inkwell::{
     context::{AsContextRef, Context},
     types::{AnyTypeEnum, BasicType, BasicTypeEnum, IntType, PointerType},
-    values::{IntValue, PointerValue},
+    values::{BasicValue, IntValue, PointerValue},
     AddressSpace,
 };
 use itertools::Itertools;
@@ -116,6 +116,19 @@ impl<'ctx> NDArrayType<'ctx> {
         NDArrayType { ty: llvm_ndarray, dtype, ndims, llvm_usize }
     }
 
+    /// Creates an instance of [`NDArrayType`] with `ndims` of 0.
+    #[must_use]
+    pub fn new_unsized<G: CodeGenerator + ?Sized>(
+        generator: &G,
+        ctx: &'ctx Context,
+        dtype: BasicTypeEnum<'ctx>,
+    ) -> Self {
+        let llvm_usize = generator.get_size_type(ctx);
+        let llvm_ndarray = Self::llvm_type(ctx, llvm_usize);
+
+        NDArrayType { ty: llvm_ndarray, dtype, ndims: Some(0), llvm_usize }
+    }
+
     /// Creates an [`NDArrayType`] from a [unifier type][Type].
     #[must_use]
     pub fn from_unifier_type<G: CodeGenerator + ?Sized>(
@@ -343,6 +356,34 @@ impl<'ctx> NDArrayType<'ctx> {
         ndarray
     }
 
+    /// Create an unsized ndarray to contain `value`.
+    #[must_use]
+    pub fn construct_unsized<G: CodeGenerator + ?Sized>(
+        &self,
+        generator: &mut G,
+        ctx: &mut CodeGenContext<'ctx, '_>,
+        value: &impl BasicValue<'ctx>,
+        name: Option<&'ctx str>,
+    ) -> NDArrayValue<'ctx> {
+        let value = value.as_basic_value_enum();
+
+        assert_eq!(value.get_type(), self.dtype);
+        assert!(self.ndims.is_none_or(|ndims| ndims == 0));
+
+        // We have to put the value on the stack to get a data pointer.
+        let data = ctx.builder.build_alloca(value.get_type(), "construct_unsized").unwrap();
+        ctx.builder.build_store(data, value).unwrap();
+        let data = ctx
+            .builder
+            .build_pointer_cast(data, ctx.ctx.i8_type().ptr_type(AddressSpace::default()), "")
+            .unwrap();
+
+        let ndarray = Self::new_unsized(generator, ctx.ctx, value.get_type())
+            .construct_uninitialized(generator, ctx, name);
+        ctx.builder.build_store(ndarray.ptr_to_data(ctx), data).unwrap();
+        ndarray
+    }
+
     /// Converts an existing value into a [`NDArrayValue`].
     #[must_use]
     pub fn map_value(