db.sqlite: fix thirdparty amalgamation not found on Linux (#26724)

* db.sqlite: fix thirdparty amalgamation not found on Linux

Make the thirdparty sqlite include path apply on all platforms,
not just Windows. On Linux, use pkg-config when the system library
is available, otherwise fall back to compiling the thirdparty
amalgamation. Update docs to reflect cross-platform support.

Closes #26723

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* db.sqlite: preserve -lsqlite3 fallback for systems without pkg-config

Keep the original -lsqlite3 fallback when pkg-config metadata is
missing, so environments with SQLite installed but no sqlite3.pc
file (e.g. default macOS SDK, some Linux/BSD setups) continue to
work without requiring the thirdparty amalgamation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* db.sqlite: prefer system sqlite via pkgconfig before thirdparty fallback

Restructure the flag chain so pkgconfig is checked first, then
Windows thirdparty, then -lsqlite3 fallback. This ensures the
system install is preferred when available.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Richard Wheeler <18647491+PythonWillRule@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

doc/docs.md

@@ -5622,9 +5622,22 @@ sql db {
 
 For more examples and the docs, see [vlib/orm](https://github.com/vlang/v/tree/master/vlib/orm).
 
-### Troubleshooting compilation problems with SQLite on Windows
-On Windows, if you get a compilation error, about a missing sqlite3.h file, you have to run:
-`v vlib/db/sqlite/install_thirdparty_sqlite.vsh` once, then retry your compilation.
+### Troubleshooting compilation problems with SQLite
+
+On **any platform** (Windows, Linux, macOS), you can run:
+
+`v vlib/db/sqlite/install_thirdparty_sqlite.vsh`
+
+This downloads the SQLite amalgamation source and places it in
+`v/thirdparty/sqlite`. V will then compile it automatically
+during your build.
+
+On **Linux**, you can also install the system development package
+instead:
+
+- Debian/Ubuntu: `sudo apt install -y libsqlite3-dev`
+- Fedora/RHEL: `sudo dnf -y install sqlite-devel`
+- Arch: `sudo pacman -S sqlite`
 
 ### Using the self contained SQLite module
 V also maintains a separate `sqlite` module, that wraps an SQLite amalgamation, but otherwise

vlib/db/sqlite/README.md

@@ -6,23 +6,20 @@ high-reliability, full-featured, SQL database engine."
 
 # Install SQLite Dependency
 
-Before you can use this module, you must first have the SQLite development
-library installed on your system.
+On **any platform** (Windows, Linux, macOS), you can run:
 
-**Fedora 31**:
+`v vlib/db/sqlite/install_thirdparty_sqlite.vsh`
 
-`sudo dnf -y install sqlite-devel`
+This downloads the SQLite amalgamation source and places it in
+`v/thirdparty/sqlite`. V will then compile it automatically
+during your build.
 
+On **Linux**, you can also install the system development package
+instead:
 
-**Ubuntu 20.04**:
-
-`sudo apt install -y libsqlite3-dev`
-
-
-**Windows**:
-- Download the source zip from [SQLite Downloads](https://sqlite.org/download.html)
-- Create a new `sqlite` subfolder inside `v/thirdparty`
-- Extract the zip into that folder
+- Debian/Ubuntu: `sudo apt install -y libsqlite3-dev`
+- Fedora/RHEL: `sudo dnf -y install sqlite-devel`
+- Arch: `sudo pacman -S sqlite`
 
 # Performance Tips
 

vlib/db/sqlite/sqlite.c.v

@@ -4,15 +4,16 @@ $if freebsd || openbsd {
 	#flag -I/usr/local/include
 	#flag -L/usr/local/lib
 }
-$if windows {
-	#flag windows -I@VEXEROOT/thirdparty/sqlite
+#flag -I@VEXEROOT/thirdparty/sqlite
+$if $pkgconfig('sqlite3') {
+	#pkgconfig sqlite3
+} $else $if windows {
 	#flag windows -L@VEXEROOT/thirdparty/sqlite
 	#flag windows @VEXEROOT/thirdparty/sqlite/sqlite3.o
-	#include "sqlite3.h" # The SQLite header file is missing. Please run vlib/db/sqlite/install_thirdparty_sqlite.vsh to download an SQLite amalgamation.
 } $else {
 	#flag -lsqlite3
-	#include "sqlite3.h" # The SQLite header file is missing. Please install its development package first.
 }
+#include "sqlite3.h" # The SQLite header file is missing. Please run vlib/db/sqlite/install_thirdparty_sqlite.vsh to download an SQLite amalgamation, or install its development package.
 
 // https://www.sqlite.org/rescode.html
 pub const sqlite_ok = 0