Fix parse tree regression handling while loop body implicit returns. (F…

…uelLabs#2414)

Take the following code as an example:

```rust
fn main() -> u64 {
    while true {
        true
    }
}
```

We were converting the body of the while to:

`CodeBlock { contents: [Expression(Literal { value: Boolean(true) })]}`

After these changes, we now convert this to:

`CodeBlock { contents: [ImplicitReturnExpression(Literal { value:
Boolean(true) })]}`

After which the existing sema checking code can correctly issue errors.

Closes FuelLabs#2401.

sway-core/src/convert_parse_tree.rs

@@ -593,7 +593,7 @@ fn item_fn_to_function_declaration(
         purity: get_attributed_purity(ec, attributes)?,
         name: item_fn.fn_signature.name,
         visibility: pub_token_opt_to_visibility(item_fn.fn_signature.visibility),
-        body: braced_code_block_contents_to_code_block(ec, item_fn.body, false)?,
+        body: braced_code_block_contents_to_code_block(ec, item_fn.body)?,
         parameters: fn_args_to_function_parameters(
             ec,
             item_fn.fn_signature.arguments.into_inner(),
@@ -919,7 +919,6 @@ fn type_field_to_enum_variant(
 fn braced_code_block_contents_to_code_block(
     ec: &mut ErrorContext,
     braced_code_block_contents: Braces<CodeBlockContents>,
-    is_while_loop_body: bool,
 ) -> Result<CodeBlock, ErrorEmitted> {
     let whole_block_span = braced_code_block_contents.span();
     let code_block_contents = braced_code_block_contents.into_inner();
@@ -930,11 +929,7 @@ fn braced_code_block_contents_to_code_block(
             contents.extend(ast_nodes);
         }
         if let Some(expr) = code_block_contents.final_expr_opt {
-            let final_ast_node = expr_to_ast_node(
-                ec,
-                *expr,
-                !is_while_loop_body, // end_of_non_while_loop_body_block
-            )?;
+            let final_ast_node = expr_to_ast_node(ec, *expr, false)?;
             contents.push(final_ast_node);
         }
         contents
@@ -1119,7 +1114,7 @@ fn path_type_to_call_path(
 fn expr_to_ast_node(
     ec: &mut ErrorContext,
     expr: Expr,
-    end_of_non_while_loop_body_block: bool,
+    is_statement: bool,
 ) -> Result<AstNode, ErrorEmitted> {
     let span = expr.span();
     let ast_node = match expr {
@@ -1141,9 +1136,7 @@ fn expr_to_ast_node(
         } => AstNode {
             content: AstNodeContent::WhileLoop(WhileLoop {
                 condition: expr_to_expression(ec, *condition)?,
-                body: braced_code_block_contents_to_code_block(
-                    ec, block, true, // is_while_loop_body
-                )?,
+                body: braced_code_block_contents_to_code_block(ec, block)?,
             }),
             span,
         },
@@ -1184,7 +1177,7 @@ fn expr_to_ast_node(
         },
         expr => {
             let expression = expr_to_expression(ec, expr)?;
-            if end_of_non_while_loop_body_block {
+            if !is_statement {
                 AstNode {
                     content: AstNodeContent::ImplicitReturnExpression(expression),
                     span,
@@ -1903,7 +1896,7 @@ fn statement_to_ast_nodes(
     let ast_nodes = match statement {
         Statement::Let(statement_let) => statement_let_to_ast_nodes(ec, statement_let)?,
         Statement::Item(item) => item_to_ast_nodes(ec, item)?,
-        Statement::Expr { expr, .. } => vec![expr_to_ast_node(ec, expr, false)?],
+        Statement::Expr { expr, .. } => vec![expr_to_ast_node(ec, expr, true)?],
     };
     Ok(ast_nodes)
 }
@@ -2169,7 +2162,7 @@ fn braced_code_block_contents_to_expression(
 ) -> Result<Expression, ErrorEmitted> {
     let span = braced_code_block_contents.span();
     Ok(Expression::CodeBlock {
-        contents: braced_code_block_contents_to_code_block(ec, braced_code_block_contents, false)?,
+        contents: braced_code_block_contents_to_code_block(ec, braced_code_block_contents)?,
         span,
     })
 }
@@ -2187,7 +2180,7 @@ fn if_expr_to_expression(
     } = if_expr;
     let then_block_span = then_block.span();
     let then_block = Expression::CodeBlock {
-        contents: braced_code_block_contents_to_code_block(ec, then_block, false)?,
+        contents: braced_code_block_contents_to_code_block(ec, then_block)?,
         span: then_block_span.clone(),
     };
     let else_block = match else_opt {
@@ -2578,7 +2571,7 @@ fn match_branch_to_match_branch(
             MatchBranchKind::Block { block, .. } => {
                 let span = block.span();
                 Expression::CodeBlock {
-                    contents: braced_code_block_contents_to_code_block(ec, block, false)?,
+                    contents: braced_code_block_contents_to_code_block(ec, block)?,
                     span,
                 }
             }

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

@@ -0,0 +1,4 @@
+[[package]]
+name = 'while_implicit_ret'
+source = 'root'
+dependencies = []

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

@@ -0,0 +1,6 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "while_implicit_ret"
+implicit-std = false

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

@@ -0,0 +1,7 @@
+script;
+
+fn main() -> u64 {
+    while true {
+        true
+    }
+}

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

@@ -0,0 +1,4 @@
+category = "fail"
+
+# unordered: $()Implicit return must match up with block's type.
+# unordered: $()A while loop's loop body cannot implicitly return a value. Try assigning it to a mutable variable declared outside of the loop instead.