From ece334b53284c2718515d35a81862712c9df06df Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Sun, 14 Jul 2024 13:42:12 +0200
Subject: [PATCH 1/3] tests/functional/repl: Characterize side effecting print
 behavior

Reported on matrix by aleksana:
https://matrix.to/#/!VRULIdgoKmKPzJZzjj:nixos.org/$7wZp5lUDTd-_u6MYo8kWWcysjtqTiQqP8dLI0RDNVVM?via=nixos.org&via=matrix.org&via=nixos.dev
---
 .../repl/pretty-print-idempotent.expected     | 33 +++++++++++++++++++
 .../repl/pretty-print-idempotent.in           |  9 +++++
 .../repl/pretty-print-idempotent.nix          | 19 +++++++++++
 3 files changed, 61 insertions(+)
 create mode 100644 tests/functional/repl/pretty-print-idempotent.expected
 create mode 100644 tests/functional/repl/pretty-print-idempotent.in
 create mode 100644 tests/functional/repl/pretty-print-idempotent.nix

diff --git a/tests/functional/repl/pretty-print-idempotent.expected b/tests/functional/repl/pretty-print-idempotent.expected
new file mode 100644
index 000000000..e74239564
--- /dev/null
+++ b/tests/functional/repl/pretty-print-idempotent.expected
@@ -0,0 +1,33 @@
+Nix <nix version>
+Type :? for help.
+Added <number omitted> variables.
+
+{
+  homepage = "https://example.com";
+}
+
+{ homepage = "https://example.com"; }
+
+{
+  layerOne = { ... };
+}
+
+{
+  layerOne = { ... };
+}
+
+[
+  "https://example.com"
+]
+
+[ "https://example.com" ]
+
+[
+  [ ... ]
+]
+
+[
+  [ ... ]
+]
+
+
diff --git a/tests/functional/repl/pretty-print-idempotent.in b/tests/functional/repl/pretty-print-idempotent.in
new file mode 100644
index 000000000..5f865316f
--- /dev/null
+++ b/tests/functional/repl/pretty-print-idempotent.in
@@ -0,0 +1,9 @@
+:l pretty-print-idempotent.nix
+oneDeep
+oneDeep
+twoDeep
+twoDeep
+oneDeepList
+oneDeepList
+twoDeepList
+twoDeepList
diff --git a/tests/functional/repl/pretty-print-idempotent.nix b/tests/functional/repl/pretty-print-idempotent.nix
new file mode 100644
index 000000000..68929f387
--- /dev/null
+++ b/tests/functional/repl/pretty-print-idempotent.nix
@@ -0,0 +1,19 @@
+{
+  oneDeep = {
+    homepage = "https://" + "example.com";
+  };
+  twoDeep = {
+    layerOne = {
+      homepage = "https://" + "example.com";
+    };
+  };
+
+  oneDeepList = [
+    ("https://" + "example.com")
+  ];
+  twoDeepList = [
+    [
+      ("https://" + "example.com")
+    ]
+  ];
+}

From a0635a80b2c3bc89baffd64b1d91d7efa2d2fd3a Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Sun, 14 Jul 2024 14:28:21 +0200
Subject: [PATCH 2/3] printAttrs: Force item before determining whether to
 print multi-line

---
 src/libexpr/print.cc                                   | 6 ++++++
 tests/functional/repl/pretty-print-idempotent.expected | 4 +---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index 2f377e588..6167abee8 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -299,6 +299,9 @@ private:
             output << ANSI_NORMAL;
     }
 
+    /**
+     * @note This may force items.
+     */
     bool shouldPrettyPrintAttrs(AttrVec & v)
     {
         if (!options.shouldPrettyPrint() || v.empty()) {
@@ -315,6 +318,9 @@ private:
             return true;
         }
 
+        // It is ok to force the item(s) here, because they will be printed anyway.
+        state.forceValue(*item, item->determinePos(noPos));
+
         // Pretty-print single-item attrsets only if they contain nested
         // structures.
         auto itemType = item->type();
diff --git a/tests/functional/repl/pretty-print-idempotent.expected b/tests/functional/repl/pretty-print-idempotent.expected
index e74239564..949d7a0e6 100644
--- a/tests/functional/repl/pretty-print-idempotent.expected
+++ b/tests/functional/repl/pretty-print-idempotent.expected
@@ -2,9 +2,7 @@ Nix <nix version>
 Type :? for help.
 Added <number omitted> variables.
 
-{
-  homepage = "https://example.com";
-}
+{ homepage = "https://example.com"; }
 
 { homepage = "https://example.com"; }
 

From da3eff60bc35763270f57c3cc17e613a19513709 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Sun, 14 Jul 2024 14:31:20 +0200
Subject: [PATCH 3/3] printList: Force item before determining whether to print
 multi-line

---
 src/libexpr/print.cc                                   | 6 ++++++
 tests/functional/repl/pretty-print-idempotent.expected | 4 +---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index 6167abee8..bc17d6bfe 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -377,6 +377,9 @@ private:
         }
     }
 
+    /**
+     * @note This may force items.
+     */
     bool shouldPrettyPrintList(std::span<Value * const> list)
     {
         if (!options.shouldPrettyPrint() || list.empty()) {
@@ -393,6 +396,9 @@ private:
             return true;
         }
 
+        // It is ok to force the item(s) here, because they will be printed anyway.
+        state.forceValue(*item, item->determinePos(noPos));
+
         // Pretty-print single-item lists only if they contain nested
         // structures.
         auto itemType = item->type();
diff --git a/tests/functional/repl/pretty-print-idempotent.expected b/tests/functional/repl/pretty-print-idempotent.expected
index 949d7a0e6..f38b9b569 100644
--- a/tests/functional/repl/pretty-print-idempotent.expected
+++ b/tests/functional/repl/pretty-print-idempotent.expected
@@ -14,9 +14,7 @@ Added <number omitted> variables.
   layerOne = { ... };
 }
 
-[
-  "https://example.com"
-]
+[ "https://example.com" ]
 
 [ "https://example.com" ]