Add error for duplicate struct field initialization (#6401)

## Description

Fixes #6378

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

Co-authored-by: Sophie Dankel <[email protected]>

sway-core/src/semantic_analysis/ast_node/expression/typed_expression/struct_instantiation.rs

@@ -1,3 +1,5 @@
+use std::collections::BTreeSet;
+
 use itertools::Itertools;
 use sway_error::{
     error::{CompileError, StructFieldUsageContext},
@@ -140,6 +142,18 @@ pub(crate) fn struct_instantiation(
         });
     }
 
+    // Check that there are no duplicate fields.
+    let mut seen_fields: BTreeSet<Ident> = BTreeSet::new();
+    for field in fields.iter() {
+        if let Some(duplicate) = seen_fields.get(&field.name) {
+            handler.emit_err(CompileError::StructFieldDuplicated {
+                field_name: field.name.clone(),
+                duplicate: duplicate.clone(),
+            });
+        }
+        seen_fields.insert(field.name.clone());
+    }
+
     // Check that there are no extra fields.
     for field in fields.iter() {
         if !struct_fields.iter().any(|x| x.name == field.name) {

sway-error/src/error.rs

@@ -368,6 +368,8 @@ pub enum CompileError {
         struct_is_empty: bool,
         usage_context: StructFieldUsageContext,
     },
+    #[error("Field \"{field_name}\" has multiple definitions.")]
+    StructFieldDuplicated { field_name: Ident, duplicate: Ident },
     #[error("No method named \"{method_name}\" found for type \"{type_name}\".")]
     MethodNotFound {
         method_name: Ident,
@@ -1071,6 +1073,7 @@ impl Spanned for CompileError {
             StructCannotBeInstantiated { span, .. } => span.clone(),
             StructFieldIsPrivate { field_name, .. } => field_name.span(),
             StructFieldDoesNotExist { field_name, .. } => field_name.span(),
+            StructFieldDuplicated { field_name, .. } => field_name.span(),
             MethodNotFound { span, .. } => span.clone(),
             ModuleNotFound { span, .. } => span.clone(),
             TupleElementAccessOnNonTuple { span, .. } => span.clone(),
@@ -2061,6 +2064,24 @@ impl ToDiagnostic for CompileError {
                 },
                 help: vec![],
             },
+            StructFieldDuplicated { field_name, duplicate } => Diagnostic {
+                reason: Some(Reason::new(code(1), "Struct field has multiple definitions".to_string())),
+                issue: Issue::error(
+                    source_engine,
+                    field_name.span(),
+                    format!("Field \"{field_name}\" has multiple definitions.")
+                ),
+                hints: {
+                    vec![
+                        Hint::info(
+                            source_engine,
+                            duplicate.span(),
+                            "Field definition duplicated here.".into(),
+                        )
+                   ]
+                },
+                help: vec![],
+            },
             NotIndexable { actually, span } => Diagnostic {
                 reason: Some(Reason::new(code(1), "Type is not indexable".to_string())),
                 issue: Issue::error(

test/src/e2e_vm_tests/test_programs/should_fail/duplicate_struct_field/Forc.lock

@@ -0,0 +1,8 @@
+[[package]]
+name = "core"
+source = "path+from-root-62266B0554A16849"
+
+[[package]]
+name = "duplicate_struct_field"
+source = "member"
+dependencies = ["core"]

test/src/e2e_vm_tests/test_programs/should_fail/duplicate_struct_field/Forc.toml

@@ -0,0 +1,9 @@
+[project]
+name = "duplicate_struct_field"
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+implicit-std = false
+
+[dependencies]
+core = { path = "../../../../../../sway-lib-core" }

test/src/e2e_vm_tests/test_programs/should_fail/duplicate_struct_field/json_abi_oracle.json

@@ -0,0 +1,35 @@
+{
+  "configurables": [],
+  "functions": [
+    {
+      "attributes": null,
+      "inputs": [],
+      "name": "bar",
+      "output": {
+        "name": "",
+        "type": 0,
+        "typeArguments": null
+      }
+    },
+    {
+      "attributes": null,
+      "inputs": [],
+      "name": "baz",
+      "output": {
+        "name": "",
+        "type": 0,
+        "typeArguments": null
+      }
+    }
+  ],
+  "loggedTypes": [],
+  "messagesTypes": [],
+  "types": [
+    {
+      "components": [],
+      "type": "()",
+      "typeId": 0,
+      "typeParameters": null
+    }
+  ]
+}

test/src/e2e_vm_tests/test_programs/should_fail/duplicate_struct_field/src/main.sw

@@ -0,0 +1,12 @@
+script;
+
+struct S {
+    x: u64,
+}
+
+pub fn main() {
+    let _ = S{
+        x:1,
+        x: "a",
+    };
+}

test/src/e2e_vm_tests/test_programs/should_fail/duplicate_struct_field/test.toml

@@ -0,0 +1,4 @@
+category = "fail"
+
+# check: $()Struct field has multiple definitions
+# check: $()Field "x" has multiple definitions.