M10: Windows without the print DLLs still starts (#2630)

pdfcraft.exe and pdfcraft-cli.exe imported windows.data.pdf.dll and
prntvpt.dll at load time (through craft-print's printing), so a trimmed
Windows installation without them refused to start the program at all.
The executables now delay-load the two DLLs, and the spool adapters
check that they exist before calling in: without them the printer list
is empty and a print job fails with a message pointing to Save as PDF.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/pdfcraft-cli/build.rs

@@ -6,12 +6,25 @@
 //! cross-compile from macOS or Linux still links, unless `PDFCRAFT_REQUIRE_WINRES=1` turns it
 //! into an error (for release builds).
 
+/// The in-box DLLs only printing uses (Windows.Data.Pdf draws the job, prntvpt reads the
+/// driver's print capabilities). Trimmed Windows installations (NTLite) can lack them, and a
+/// load-time import of a missing DLL stops the program before `main` (#2630). Delay-loaded, they
+/// load on the first print; `pdfcraft_print::spool` checks they exist before calling in.
+/// Same list in `apps/pdfcraft{,-cli}/build.rs` and `crates/print/src/spool.rs`.
+const DELAY_LOADED: [&str; 2] = ["windows.data.pdf.dll", "prntvpt.dll"];
+
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-env-changed=PDFCRAFT_REQUIRE_WINRES");
     if std::env::var("CARGO_CFG_TARGET_OS").as_deref() != Ok("windows") {
         return;
     }
+    if std::env::var("CARGO_CFG_TARGET_ENV").as_deref() == Ok("msvc") {
+        for dll in DELAY_LOADED {
+            println!("cargo:rustc-link-arg-bins=/DELAYLOAD:{dll}");
+        }
+        println!("cargo:rustc-link-arg-bins=delayimp.lib");
+    }
     let mut res = winresource::WindowsResource::new();
     res.set("ProductName", "PdfCraft")
         .set("FileDescription", "PdfCraft command-line tool")

apps/pdfcraft/build.rs

@@ -9,6 +9,13 @@
 #[path = "src/windows_manifest.rs"]
 mod windows_manifest;
 
+/// The in-box DLLs only printing uses (Windows.Data.Pdf draws the job, prntvpt reads the
+/// driver's print capabilities). Trimmed Windows installations (NTLite) can lack them, and a
+/// load-time import of a missing DLL stops the program before `main` (#2630). Delay-loaded, they
+/// load on the first print; `pdfcraft_print::spool` checks they exist before calling in.
+/// Same list in `apps/pdfcraft{,-cli}/build.rs` and `crates/print/src/spool.rs`.
+const DELAY_LOADED: [&str; 2] = ["windows.data.pdf.dll", "prntvpt.dll"];
+
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=../../assets/app-icon/pdfcraft.ico");
@@ -18,6 +25,12 @@ fn main() {
     if std::env::var("CARGO_CFG_TARGET_OS").as_deref() != Ok("windows") {
         return;
     }
+    if std::env::var("CARGO_CFG_TARGET_ENV").as_deref() == Ok("msvc") {
+        for dll in DELAY_LOADED {
+            println!("cargo:rustc-link-arg-bins=/DELAYLOAD:{dll}");
+        }
+        println!("cargo:rustc-link-arg-bins=delayimp.lib");
+    }
     let mut res = winresource::WindowsResource::new();
     res.set_icon("../../assets/app-icon/pdfcraft.ico")
         .set_icon_with_id("../../assets/app-icon/pdfcraft-document.ico", "2")

crates/print/src/spool.rs

@@ -3,9 +3,46 @@
 
 pub use craft_print::{
     Duplex, HANDLED_OPTIONS, HAS_PRINTER_PREFERENCES, Job, Printer, PrinterOption, Scaling, lp_args, lpstat_command, parse_lpoptions, parse_lpstat,
-    parse_lpstat_e, parse_ppd, parse_windows_printers, ppd_text, printers, printers_parsed,
+    parse_lpstat_e, parse_ppd, parse_windows_printers, ppd_text, printers_parsed,
 };
 
+/// Windows: the in-box DLLs printing draws and describes jobs with. The executables delay-load
+/// them (`apps/pdfcraft{,-cli}/build.rs`, the same list) so a Windows installation without them
+/// still starts (#2630); a call into a missing delay-loaded DLL would end the process, so
+/// printing checks for them first.
+#[cfg(windows)]
+pub(crate) const PRINT_DLLS: [&str; 2] = ["windows.data.pdf.dll", "prntvpt.dll"];
+
+/// The first print DLL missing from `system32`, if any.
+#[cfg(windows)]
+pub(crate) fn missing_print_dll_in(system32: &std::path::Path) -> Option<&'static str> {
+    PRINT_DLLS.into_iter().find(|dll| !system32.join(dll).is_file())
+}
+
+/// The first print DLL this Windows installation lacks. `None` when all are there, and when the
+/// system folder is unknown (the loader then decides, as before).
+fn missing_print_dll() -> Option<&'static str> {
+    #[cfg(windows)]
+    {
+        let root = std::env::var_os("SystemRoot").or_else(|| std::env::var_os("windir"))?;
+        missing_print_dll_in(&std::path::Path::new(&root).join("System32"))
+    }
+    #[cfg(not(windows))]
+    None
+}
+
+fn unavailable(dll: &str) -> crate::PrintError {
+    crate::PrintError::Spool(format!("printing needs {dll}, which this Windows installation lacks; use Save as PDF instead"))
+}
+
+/// The system's printers; none on a Windows installation without the print DLLs.
+pub fn printers() -> Vec<Printer> {
+    if missing_print_dll().is_some() {
+        return Vec::new();
+    }
+    craft_print::printers()
+}
+
 /// The driver's job options for a printer (CUPS: its PPD, with the queue's current defaults);
 /// empty when it has none or on other platforms. Reads files and runs `lpoptions`, so call it
 /// when the user asks, not every frame.
@@ -144,12 +181,18 @@ pub(crate) fn printer_options_via_within(
 }
 
 pub fn submit(pdf: &[u8], job: &Job) -> Result<String, crate::PrintError> {
+    if let Some(dll) = missing_print_dll() {
+        return Err(unavailable(dll));
+    }
     craft_print::submit(pdf, job).map_err(|e| crate::PrintError::Spool(e.to_string()))
 }
 
 /// [`submit`], told `(sent, sheets)` as each sheet reaches the spooler (Windows; CUPS takes the
 /// whole PDF at once and reports nothing).
 pub fn submit_with_progress(pdf: &[u8], job: &Job, progress: &mut dyn FnMut(usize, usize)) -> Result<String, crate::PrintError> {
+    if let Some(dll) = missing_print_dll() {
+        return Err(unavailable(dll));
+    }
     craft_print::submit_with_progress(pdf, job, progress).map_err(|e| crate::PrintError::Spool(e.to_string()))
 }
 

crates/print/src/tests.rs

@@ -1144,3 +1144,23 @@ fn contents_pieces_join_with_a_space_across_a_trailing_comment() {
     let printed_ctrl = impose(&with_newline, &settings(vec![0], Layout::Size(SizeMode::Actual))).unwrap();
     assert_eq!(form_strings(printed_ctrl), [b"HIDDEN".to_vec(), b"SHOWN".to_vec()]);
 }
+
+/// #2630: a Windows installation without the print DLLs is told so, before anything calls into
+/// a delay-loaded DLL that is not there.
+#[cfg(windows)]
+#[test]
+fn missing_print_dlls_are_named() {
+    use crate::spool::{PRINT_DLLS, missing_print_dll_in};
+    let dir = std::env::temp_dir().join(format!("pdfcraft-print-dlls-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    assert_eq!(missing_print_dll_in(&dir), Some(PRINT_DLLS[0]));
+    std::fs::write(dir.join(PRINT_DLLS[0]), b"").unwrap();
+    assert_eq!(missing_print_dll_in(&dir), Some(PRINT_DLLS[1]));
+    std::fs::write(dir.join(PRINT_DLLS[1]), b"").unwrap();
+    assert_eq!(missing_print_dll_in(&dir), None);
+    let _ = std::fs::remove_dir_all(&dir);
+    // This machine's own Windows has them.
+    let system32 = std::path::Path::new(&std::env::var_os("SystemRoot").unwrap()).join("System32");
+    assert_eq!(missing_print_dll_in(&system32), None);
+}