fix(ssa): Accurate constant type for slice dummy data in flattening (#…

…4661)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

We were not accurately constructing the type for slice dummy data. We
were always making slice dummy data a `Field` but this could lead to
errors when eventually merging this value with a different numeric type.

## Additional Context



## Documentation\*

Check one:
- [ ] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [ ] I have tested the changes locally.
- [ ] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_evaluator/src/ssa/opt/flatten_cfg/value_merger.rs

@@ -234,9 +234,9 @@ impl<'a> ValueMerger<'a> {
     /// such as with dynamic indexing of non-homogenous slices.
     fn make_slice_dummy_data(&mut self, typ: &Type) -> ValueId {
         match typ {
-            Type::Numeric(_) => {
+            Type::Numeric(numeric_type) => {
                 let zero = FieldElement::zero();
-                self.dfg.make_constant(zero, Type::field())
+                self.dfg.make_constant(zero, Type::Numeric(*numeric_type))
             }
             Type::Array(element_types, len) => {
                 let mut array = im::Vector::new();

test_programs/execution_success/regression_sha256_slice/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "regression_sha256_slice"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.26.0"
+
+[dependencies]

test_programs/execution_success/regression_sha256_slice/Prover.toml

@@ -0,0 +1 @@
+x = ["5", "10"]

test_programs/execution_success/regression_sha256_slice/src/main.nr

@@ -0,0 +1,12 @@
+use dep::std;
+
+fn main(x: [u8; 2]) {
+    let mut y = x.as_slice();
+    let digest1 = std::hash::sha256_slice(y);
+    let mut v = y;
+    if x[0] != 0 {
+        v = y.push_back(x[0]);
+    }
+    let digest2 = std::hash::sha256_slice(v);
+    assert(digest1 != digest2);
+}