From 1c958e85251c83e4ca24c2a7490a4b9e8458f07b Mon Sep 17 00:00:00 2001
From: Ilja Heitlager <iheitlager@schubergphilis.com>
Date: Mon, 31 Aug 2026 11:39:45 +0200
Subject: [PATCH] perf: leak names in
 BtreeError::InvalidRootPage/MasterEntryNotFound

Replaces the owned `String` in these two cold sqlite_master
corruption/lookup variants with a leaked `&'static str`, removing their
drop glue. This is intentional: both variants are only constructed on
rare error paths (corrupt rootpage, missing schema entry during
delete), so leaking the handful of bytes is a deliberate trade against
the drop cost these variants otherwise impose on every
Result<_, BtreeError> in TableCursor::seek's hot per-page binary
search.

std::mem::needs_drop::<BtreeError>() still returns true overall
because BtreeError::Pager(PagerError) transitively owns a
`path: String` (PagerError::HotJournal/Wal) -- fixing that is a
separate, out-of-scope change (see PR description).

Refs: follow-up to #677, closes #679
---
 src/btree/error.rs  | 19 ++++++++++++-------
 src/btree/master.rs |  6 +++---
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/btree/error.rs b/src/btree/error.rs
index d2660ec3..28100efb 100644
--- a/src/btree/error.rs
+++ b/src/btree/error.rs
@@ -131,17 +131,25 @@ pub enum BtreeError {
     KeyNotFound,
 
     /// A `sqlite_master` entry names a rootpage number outside the valid page range.
+    ///
+    /// `name` is leaked (via [`Box::leak`]) rather than owned as a `String`:
+    /// this is a cold, rare corruption-detection path, and leaking here keeps
+    /// `BtreeError` itself free of drop glue (`needs_drop::<BtreeError>() ==
+    /// false`), which matters because it is constructed on the hot
+    /// `TableCursor::seek` path (see #679).
     InvalidRootPage {
         /// Name of the offending `sqlite_master` entry.
-        name: String,
+        name: &'static str,
         /// Out-of-range rootpage value.
         rootpage: i64,
     },
 
     /// A delete targeted a `sqlite_master` entry that does not exist.
+    ///
+    /// `name` is leaked for the same reason as [`BtreeError::InvalidRootPage`].
     MasterEntryNotFound {
         /// Name of the entry that could not be found.
-        name: String,
+        name: &'static str,
     },
 
     /// An internal invariant was violated; the message describes what was expected.
@@ -369,17 +377,14 @@ mod tests {
         );
         assert_eq!(
             BtreeError::InvalidRootPage {
-                name: "t".to_string(),
+                name: "t",
                 rootpage: -1
             }
             .to_string(),
             "sqlite_master entry \"t\" has out-of-range rootpage -1"
         );
         assert_eq!(
-            BtreeError::MasterEntryNotFound {
-                name: "t".to_string()
-            }
-            .to_string(),
+            BtreeError::MasterEntryNotFound { name: "t" }.to_string(),
             "cannot delete sqlite_master entry \"t\": no such entry"
         );
         assert_eq!(
diff --git a/src/btree/master.rs b/src/btree/master.rs
index 5e9cf618..6ff8fdb3 100644
--- a/src/btree/master.rs
+++ b/src/btree/master.rs
@@ -168,7 +168,7 @@ pub fn delete_master_row(
         header.text_encoding,
     )?
     .ok_or_else(|| BtreeError::MasterEntryNotFound {
-        name: name.to_string(),
+        name: Box::leak(name.to_string().into_boxed_str()),
     })?;
     super::delete_row(pager, header, SQLITE_MASTER_ROOT_PAGE, rowid)
 }
@@ -225,12 +225,12 @@ fn find_master_rootpage(
         if let (Some(Value::Text(n)), Some(Value::Integer(rp))) = (values.get(1), values.get(3)) {
             if n.as_ref() == name {
                 let rootpage = u32::try_from(*rp).map_err(|_| BtreeError::InvalidRootPage {
-                    name: name.to_string(),
+                    name: Box::leak(name.to_string().into_boxed_str()),
                     rootpage: *rp,
                 })?;
                 if rootpage == 0 {
                     return Err(BtreeError::InvalidRootPage {
-                        name: name.to_string(),
+                        name: Box::leak(name.to_string().into_boxed_str()),
                         rootpage: *rp,
                     });
                 }