Fix collapsed if stmt formatting when block begins with empty line

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed LuaJIT suffixes `LL`/`ULL` causing a panic when running in `--verify` mode ([#750](https://github.com/JohnnyMorganz/StyLua/issues/750))
+- Fixed incorrect formatting of conditionals when `collapse_simple_statement` is enabled and the block begins with an empty line ([#744](https://github.com/JohnnyMorganz/StyLua/issues/744))
 
 ## [0.18.1] - 2023-07-15
 

src/formatters/stmt.rs

@@ -468,8 +468,12 @@ pub fn format_if(ctx: &Context, if_node: &If, shape: Shape) -> If {
         // Rather than deferring to `format_block()`, since we know that there is only a single Stmt or LastStmt in the block, we can format it immediately
         // We need to modify the formatted LastStmt, since it will have automatically added leading/trailing trivia we don't want
         // We assume that there is only a laststmt present in the block - the callee of this function should have already checked for this
-        let stmt_leading_trivia = FormatTriviaType::Append(vec![Token::new(TokenType::spaces(1))]);
-        let stmt_trailing_trivia = FormatTriviaType::Append(vec![Token::new(TokenType::spaces(1))]);
+        // INVARIANT: this stmt has no leading/trailing comments, as this is checked in `is_if_guard`
+        // This means we can replace trivia completely
+        debug_assert!(!trivia_util::contains_comments(if_node.block()));
+        let stmt_leading_trivia = FormatTriviaType::Replace(vec![Token::new(TokenType::spaces(1))]);
+        let stmt_trailing_trivia =
+            FormatTriviaType::Replace(vec![Token::new(TokenType::spaces(1))]);
 
         let block = if let Some(stmt) = if_node.block().stmts().next() {
             let stmt = format_stmt_no_trivia(ctx, stmt, singleline_shape)

tests/inputs-collapse-single-statement/simple-conditional-2.lua

@@ -0,0 +1,6 @@
+-- https://github.com/JohnnyMorganz/StyLua/issues/744
+
+if tabnr ~= finaltab then
+
+	stack:push('%T')
+end

tests/snapshots/tests__collapse_single_statement@simple-conditional-2.lua.snap

@@ -0,0 +1,8 @@
+---
+source: tests/tests.rs
+expression: "format_code(&contents,\n        Config::default().with_collapse_simple_statement(CollapseSimpleStatement::Always),\n        None, OutputVerification::None).unwrap()"
+---
+-- https://github.com/JohnnyMorganz/StyLua/issues/744
+
+if tabnr ~= finaltab then stack:push("%T") end
+