From eff0f8f1d5a19f11e8f8302d70a527475b5e80b4 Mon Sep 17 00:00:00 2001
From: loicb <me@loicb.dev>
Date: Tue, 1 Sep 2026 09:42:15 +0800
Subject: [PATCH] fix(io): spit truncates on write and honours :append (#32)

file-mode returned FileMode/OpenOrCreate for every write, so an existing
file was opened at position 0 without truncating, and :append was ignored.
A plain write now opens with FileMode/Create and :append with
FileMode/Append, matching JVM Clojure.
---
 CHANGES_FLYBOT.md                             | 10 +++++++++
 Clojure/Clojure.Source/clojure/clr/io.clj     |  7 +++---
 .../clojure/test_clojure/clr/io.clj           | 22 +++++++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/CHANGES_FLYBOT.md b/CHANGES_FLYBOT.md
index facb6e322..502d0c275 100644
--- a/CHANGES_FLYBOT.md
+++ b/CHANGES_FLYBOT.md
@@ -9,6 +9,16 @@ still under Backports.
 upstream commit it came from. *(partial)* means only some hunks of that commit
 were taken.
 
+# Changes to ClojureCLR in Version 1.11.0-flybot4 (unreleased)
+
+## Fixes
+
+* [#32](https://github.com/flybot-sg/clojure-clr/pull/32) `file-mode` opens a
+  plain write with `FileMode/Create` and `:append` with `FileMode/Append`
+  instead of `FileMode/OpenOrCreate` for every write, so `spit` and `writer`
+  truncate the file they overwrite and `:append` appends, like JVM Clojure,
+  instead of writing at position 0 and dropping the option
+
 # Changes to ClojureCLR in Version 1.11.0-flybot3
 
 ## Fixes
diff --git a/Clojure/Clojure.Source/clojure/clr/io.clj b/Clojure/Clojure.Source/clojure/clr/io.clj
index 54fc21f23..a8d0d493f 100644
--- a/Clojure/Clojure.Source/clojure/clr/io.clj
+++ b/Clojure/Clojure.Source/clojure/clr/io.clj
@@ -219,9 +219,10 @@
   
 (defn- ^FileMode file-mode [mode opts]
   (or (:file-mode opts)
-      (if (= mode :read)
-          FileMode/Open
-          FileMode/OpenOrCreate)))
+      (cond
+        (= mode :read) FileMode/Open
+        (:append opts) FileMode/Append
+        :else          FileMode/Create)))
   
 (defn- ^FileShare file-share [opts]
   (or (:file-share opts) FileShare/None))
diff --git a/Clojure/Clojure.Tests/clojure/test_clojure/clr/io.clj b/Clojure/Clojure.Tests/clojure/test_clojure/clr/io.clj
index 1fa7087ff..ba722a322 100644
--- a/Clojure/Clojure.Tests/clojure/test_clojure/clr/io.clj
+++ b/Clojure/Clojure.Tests/clojure/test_clojure/clr/io.clj
@@ -62,6 +62,28 @@
               (platform-newlines "WARNING: (slurp f enc) is deprecated, use (slurp f :encoding enc).\n")
               (with-out-str
                 (is (= content (slurp f utf16))))))))))
+
+(deftest test-spit-truncates
+  (with-temp-file [f]
+    (spit f "DATA-PRESENT")
+    (spit f "AB")
+    (is (= "AB" (slurp f))))
+  (with-temp-file [f]
+    (spit f "DATA-PRESENT")
+    (spit f nil)
+    (is (= "" (slurp f)))))
+
+(deftest test-spit-append
+  (with-temp-file [f]
+    (spit f "AAA")
+    (spit f "BBB" :append true)
+    (is (= "AAABBB" (slurp f)))))
+
+(deftest test-spit-file-mode-overrides
+  (with-temp-file [f]
+    (spit f "AAA")
+    (spit f "BBB" :file-mode FileMode/Append)
+    (is (= "AAABBB" (slurp f)))))
   
 (deftest test-streams-defaults
   (let [f (temp-file "test-reader-writer")