From 28a9ba136bce06b9d08e295735c32cd2f5132692 Mon Sep 17 00:00:00 2001
From: Alexander Esgen <alexander.esgen@tweag.io>
Date: Mon, 19 Jun 2023 22:19:20 +0200
Subject: [PATCH] Preserve necessary braces for final function arguments

---
 CHANGELOG.md                                  |  5 +++++
 data/examples/other/necessary-brackets-out.hs |  3 +++
 data/examples/other/necessary-brackets.hs     |  3 +++
 src/Ormolu/Printer/Meat/Declaration/Value.hs  | 15 ++++++++++++---
 4 files changed, 23 insertions(+), 3 deletions(-)
 create mode 100644 data/examples/other/necessary-brackets-out.hs
 create mode 100644 data/examples/other/necessary-brackets.hs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 82202a3b..ac1e77e6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Unreleased
+
+* Preserve necessary braces for final function arguments. [Issue
+  1044](https://github.com/tweag/ormolu/issues/1044).
+
 ## Ormolu 0.7.1.0
 
 * Include `base` fixity information when formatting a Haskell file that's
diff --git a/data/examples/other/necessary-brackets-out.hs b/data/examples/other/necessary-brackets-out.hs
new file mode 100644
index 00000000..0c5b439e
--- /dev/null
+++ b/data/examples/other/necessary-brackets-out.hs
@@ -0,0 +1,3 @@
+insertEmDash = Text.concat . map \case { x | x == "--" -> "—"; x -> x } . Text.groupBy ((==) `on` Char.isSpace)
+
+foo f a b c = f do { a } + f do { b } + f do c
diff --git a/data/examples/other/necessary-brackets.hs b/data/examples/other/necessary-brackets.hs
new file mode 100644
index 00000000..519701f6
--- /dev/null
+++ b/data/examples/other/necessary-brackets.hs
@@ -0,0 +1,3 @@
+insertEmDash = Text.concat . map \case{ x | x == "--" -> "—"; x -> x } . Text.groupBy ((==) `on` Char.isSpace)
+
+foo f a b c = f do {a} + f do {b} + f do {c}
diff --git a/src/Ormolu/Printer/Meat/Declaration/Value.hs b/src/Ormolu/Printer/Meat/Declaration/Value.hs
index b377e07e..a0507b84 100644
--- a/src/Ormolu/Printer/Meat/Declaration/Value.hs
+++ b/src/Ormolu/Printer/Meat/Declaration/Value.hs
@@ -489,9 +489,18 @@ p_stmts ::
 p_stmts isApp placer render es = do
   breakpoint
   ub <- layoutToBraces <$> getLayout
+  let p_stmtExt (relPos, stmt) =
+        ub' $ withSpacing (p_stmt' placer render) stmt
+        where
+          -- We need to set brace usage information for all but the last
+          -- statement (e.g.in the case of nested do blocks).
+          ub' = case relPos of
+            FirstPos -> ub
+            MiddlePos -> ub
+            LastPos -> id
+            SinglePos -> id
   inciApplicand isApp . located es $
-    sepSemi
-      (ub . withSpacing (p_stmt' placer render))
+    sepSemi p_stmtExt . attachRelativePos
 
 gatherStmt :: ExprLStmt GhcPs -> [[ExprLStmt GhcPs]]
 gatherStmt (L _ (ParStmt _ block _ _)) =
@@ -654,7 +663,7 @@ p_hsExpr' isApp s = \case
           located func (p_hsExpr' Applicand s)
           breakpoint
           sep breakpoint (located' p_hsExpr) initp
-        placeHanging placement . dontUseBraces $
+        placeHanging placement $
           located lastp p_hsExpr
   HsAppType _ e _ a -> do
     located e p_hsExpr