From 2b6459cb789377a2559243f810f944b51aea0cd6 Mon Sep 17 00:00:00 2001
From: Omar Jatoi <git@omarjatoi.com>
Date: Sat, 7 Feb 2026 14:02:41 -0500
Subject: [PATCH] Fix parser warnings order

See https://github.com/haskell/cabal/issues/11269 for more information. This PR sorts the parse results by position so they're displayed in file order.

Resolves: #11269
---
 Cabal-syntax/src/Distribution/Fields/ParseResult.hs    | 10 ++++++----
 .../tests/ParserTests/regressions/common.format        |  4 ++--
 Cabal-tests/tests/ParserTests/regressions/elif.format  |  2 +-
 .../ParserTests/regressions/wl-pprint-indef.format     |  4 ++--
 changelog.d/issue-11269.md                             | 10 ++++++++++
 5 files changed, 21 insertions(+), 9 deletions(-)
 create mode 100644 changelog.d/issue-11269.md

diff --git a/Cabal-syntax/src/Distribution/Fields/ParseResult.hs b/Cabal-syntax/src/Distribution/Fields/ParseResult.hs
index 6c2dbe5e552..0abb2e3c54b 100644
--- a/Cabal-syntax/src/Distribution/Fields/ParseResult.hs
+++ b/Cabal-syntax/src/Distribution/Fields/ParseResult.hs
@@ -68,12 +68,14 @@ runParseResult pr = unPR pr emptyPRState initialCtx failure success
   where
     initialCtx = PRContext PUnknownSource
 
-    failure (PRState warns [] v) = (warns, Left (v, PErrorWithSource PUnknownSource (PError zeroPos "panic") :| []))
-    failure (PRState warns (err : errs) v) = (warns, Left (v, err :| errs))
+    failure (PRState warns [] v) = (sortWarns warns, Left (v, PErrorWithSource PUnknownSource (PError zeroPos "panic") :| []))
+    failure (PRState warns (err : errs) v) = (sortWarns warns, Left (v, err :| errs))
 
-    success (PRState warns [] _) x = (warns, Right x)
+    success (PRState warns [] _) x = (sortWarns warns, Right x)
     -- If there are any errors, don't return the result
-    success (PRState warns (err : errs) v) _ = (warns, Left (v, err :| errs))
+    success (PRState warns (err : errs) v) _ = (sortWarns warns, Left (v, err :| errs))
+
+    sortWarns = sortBy (comparing (pwarningPosition . pwarning))
 
 -- | Chain parsing operations that involve 'IO' actions.
 liftParseResult :: (a -> IO (ParseResult src b)) -> ParseResult src a -> IO (ParseResult src b)
diff --git a/Cabal-tests/tests/ParserTests/regressions/common.format b/Cabal-tests/tests/ParserTests/regressions/common.format
index 7fb317a16a5..6f46a4cbc04 100644
--- a/Cabal-tests/tests/ParserTests/regressions/common.format
+++ b/Cabal-tests/tests/ParserTests/regressions/common.format
@@ -1,6 +1,6 @@
-common.cabal:29:3: Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas
-common.cabal:20:3: Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas
 common.cabal:14:1: Ignoring section: common. You should set cabal-version: 2.2 or larger to use common stanzas.
+common.cabal:20:3: Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas
+common.cabal:29:3: Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas
 cabal-version:            >=1.10
 name:                     common
 version:                  0
diff --git a/Cabal-tests/tests/ParserTests/regressions/elif.format b/Cabal-tests/tests/ParserTests/regressions/elif.format
index 949d4432c1f..e55d76716c7 100644
--- a/Cabal-tests/tests/ParserTests/regressions/elif.format
+++ b/Cabal-tests/tests/ParserTests/regressions/elif.format
@@ -1,5 +1,5 @@
-elif.cabal:19:3: invalid subsection "else"
 elif.cabal:17:3: invalid subsection "elif". You should set cabal-version: 2.2 or larger to use elif-conditionals.
+elif.cabal:19:3: invalid subsection "else"
 cabal-version: >=1.10
 name:          elif
 version:       0
diff --git a/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.format b/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.format
index 1a16e964b06..7290991fc61 100644
--- a/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.format
+++ b/Cabal-tests/tests/ParserTests/regressions/wl-pprint-indef.format
@@ -1,6 +1,6 @@
-wl-pprint-indef.cabal:28:3: The field "mixins" is available only since the Cabal specification version 2.0. This field will be ignored.
-wl-pprint-indef.cabal:27:3: The field "signatures" is available only since the Cabal specification version 2.0. This field will be ignored.
 wl-pprint-indef.cabal:23:3: The field "mixins" is available only since the Cabal specification version 2.0. This field will be ignored.
+wl-pprint-indef.cabal:27:3: The field "signatures" is available only since the Cabal specification version 2.0. This field will be ignored.
+wl-pprint-indef.cabal:28:3: The field "mixins" is available only since the Cabal specification version 2.0. This field will be ignored.
 cabal-version: >=1.6
 name:          wl-pprint-indef
 version:       1.2
diff --git a/changelog.d/issue-11269.md b/changelog.d/issue-11269.md
new file mode 100644
index 00000000000..b1eebc203f7
--- /dev/null
+++ b/changelog.d/issue-11269.md
@@ -0,0 +1,10 @@
+---
+synopsis: Fix parse warnings being emitted in reverse order
+packages: [Cabal-syntax]
+prs: 11479
+issues: 11269
+---
+
+Parse warnings were prepended to the accumulator list, causing them to
+be emitted in reverse file order. They are now sorted so they come out
+in file order, consistent with GHC's behavior.