feat: add TypedExpr::get_type (#5992)

# Description

## Problem

Part of #5668

## Summary

## Additional Context



## Documentation

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

# PR Checklist

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

---------

Co-authored-by: jfecher <[email protected]>

compiler/noirc_frontend/src/hir/comptime/interpreter/builtin.rs

@@ -189,6 +189,9 @@ impl<'local, 'context> Interpreter<'local, 'context> {
             "typed_expr_as_function_definition" => {
                 typed_expr_as_function_definition(interner, arguments, return_type, location)
             }
+            "typed_expr_get_type" => {
+                typed_expr_get_type(interner, arguments, return_type, location)
+            }
             "unresolved_type_is_field" => unresolved_type_is_field(interner, arguments, location),
             "zeroed" => zeroed(return_type),
             _ => {
@@ -1070,6 +1073,7 @@ fn trait_impl_trait_generic_args(
     Ok(Value::Slice(trait_generics, slice_type))
 }
 
+// fn as_function_definition(self) -> Option<FunctionDefinition>
 fn typed_expr_as_function_definition(
     interner: &NodeInterner,
     arguments: Vec<(Value, Location)>,
@@ -1087,6 +1091,28 @@ fn typed_expr_as_function_definition(
     option(return_type, option_value)
 }
 
+// fn get_type(self) -> Option<Type>
+fn typed_expr_get_type(
+    interner: &NodeInterner,
+    arguments: Vec<(Value, Location)>,
+    return_type: Type,
+    location: Location,
+) -> IResult<Value> {
+    let self_argument = check_one_argument(arguments, location)?;
+    let typed_expr = get_typed_expr(self_argument)?;
+    let option_value = if let TypedExpr::ExprId(expr_id) = typed_expr {
+        let typ = interner.id_type(expr_id);
+        if typ == Type::Error {
+            None
+        } else {
+            Some(Value::Type(typ))
+        }
+    } else {
+        None
+    };
+    option(return_type, option_value)
+}
+
 // fn is_field(self) -> bool
 fn unresolved_type_is_field(
     interner: &NodeInterner,

docs/docs/noir/standard_library/meta/typed_expr.md

@@ -6,8 +6,14 @@ title: TypedExpr
 
 ## Methods
 
-### as_function_definition
+### get_type
 
 #include_code as_function_definition noir_stdlib/src/meta/typed_expr.nr rust
 
-If this expression refers to a function definitions, returns it. Otherwise returns `Option::none()`.
+If this expression refers to a function definitions, returns it. Otherwise returns `Option::none()`.
+
+### get_type
+
+#include_code get_type noir_stdlib/src/meta/typed_expr.nr rust
+
+Returns the type of the expression, or `Option::none()` if there were errors when the expression was previously resolved.

noir_stdlib/src/meta/typed_expr.nr

@@ -1,8 +1,16 @@
+//! Contains methods on the built-in `TypedExpr` type for resolved and type-checked expressions.
 use crate::option::Option;
 
 impl TypedExpr {
+    /// If this expression refers to a function definitions, returns it. Otherwise returns `Option::none()`.
     #[builtin(typed_expr_as_function_definition)]
     // docs:start:as_function_definition
     comptime fn as_function_definition(self) -> Option<FunctionDefinition> {}
     // docs:end:as_function_definition
+
+    /// Returns the type of the expression, if the expression could be resolved without errors.
+    #[builtin(typed_expr_get_type)]
+    // docs:start:get_type
+    comptime fn get_type(self) -> Option<Type> {}
+    // docs:end:get_type
 }

test_programs/compile_success_empty/comptime_typed_expr/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "comptime_typed_expr"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.31.0"
+
+[dependencies]

test_programs/compile_success_empty/comptime_typed_expr/src/main.nr

@@ -0,0 +1,7 @@
+fn main() {
+    comptime
+    {
+        let expr = quote { [1, 3] }.as_expr().unwrap().resolve(Option::none());
+        assert_eq(expr.get_type().unwrap(), quote { [Field; 2] }.as_type());
+    }
+}