database/sql: wrap errors with %w in driverArgsConnLocked

Use fmt.Errorf %w verb to wrap errors in driverArgsConnLocked,
which allows for easier unwrapping and checking of error types.

Add tests in sql_test.go to ensure that Stmt.Exec and Stmt.Query
correctly wrap underlying Valuer errors, adhering to the new change.

Fixes #64707.

Change-Id: Id9f80e265735d0849ee7abba63e58e4c26e658ad
GitHub-Last-Rev: 0df367e0fb5b213513d4e0ab7f5a87984798f96d
GitHub-Pull-Request: golang/go#64728
Reviewed-on: https://go-review.googlesource.com/c/go/+/550116
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/database/sql/driver/types.go b/src/database/sql/driver/types.go
index 0380572ab1..a322f85277 100644
--- a/src/database/sql/driver/types.go
+++ b/src/database/sql/driver/types.go
@@ -34,6 +34,10 @@ type ValueConverter interface {
 
 // Valuer is the interface providing the Value method.
 //
+// Errors returned by the [Value] method are wrapped by the database/sql package.
+// This allows callers to use [errors.Is] for precise error handling after operations
+// like [database/sql.Query], [database/sql.Exec], or [database/sql.QueryRow].
+//
 // Types implementing Valuer interface are able to convert
 // themselves to a driver [Value].
 type Valuer interface {