[librsvg/rustify-rsvg-convert: 69/78] rsvg-convert: Figure out support for Cairo surface backends

[Sven Neumann <sneumann src gnome org>]

commit 75219746cfd73a950d870a506c7da1a6b8017b64
Author: Sven Neumann <sven svenfoo org>
Date:   Tue Jan 26 23:03:17 2021 +0100

    rsvg-convert: Figure out support for Cairo surface backends
    
    Use pkg-config to figure out at compile-time what surface backends
    are supported by cairo. Change rsvg-convert to only allow supported
    output formats.

 build.rs                | 27 +++++++++++++++++++++++++--
 src/bin/rsvg-convert.rs | 15 ++++++++++++++-
 2 files changed, 39 insertions(+), 3 deletions(-)
---
diff --git a/build.rs b/build.rs
index 3a73d6bd..52081685 100644
--- a/build.rs
+++ b/build.rs
@@ -8,15 +8,20 @@ use std::process;
 
 use pkg_config::{Config, Error};
 
+const CAIRO_REQUIRED_VERSION: &str = "1.16";
+const PANGO_REQUIRED_VERSION: &str = "1.38";
+const LIBXML_REQUIRED_VERSION: &str = "2.9.0";
+
 fn main() {
     find_libxml2();
     check_for_pangoft2();
+    check_for_cairo_surface_backends();
     generate_srgb_tables();
     write_version();
 }
 
 fn find_libxml2() {
-    if let Err(s) = find("libxml-2.0", "2.9.0", &["xml2"]) {
+    if let Err(s) = find("libxml-2.0", LIBXML_REQUIRED_VERSION, &["xml2"]) {
         let _ = writeln!(io::stderr(), "{}", s);
         process::exit(1);
     }
@@ -73,7 +78,7 @@ fn find(package_name: &str, version: &str, shared_libs: &[&str]) -> Result<(), E
 
 fn check_for_pangoft2() {
     if pkg_config::Config::new()
-        .atleast_version("1.38")
+        .atleast_version(PANGO_REQUIRED_VERSION)
         .probe("pangoft2")
         .is_ok()
     {
@@ -81,6 +86,24 @@ fn check_for_pangoft2() {
     }
 }
 
+fn check_for_cairo_surface_backend(backend: &str) {
+    let pkg_name = ["cairo", backend].join("-");
+    if pkg_config::Config::new()
+        .atleast_version(CAIRO_REQUIRED_VERSION)
+        .probe(&pkg_name)
+        .is_ok()
+    {
+        println!("cargo:rustc-cfg=have_cairo_{}", backend);
+    }
+}
+
+fn check_for_cairo_surface_backends() {
+    let backends = ["pdf", "ps", "svg", "xml"];
+    for name in &backends {
+        check_for_cairo_surface_backend(name);
+    }
+}
+
 /// Converts an sRGB color value to a linear sRGB color value (undoes the gamma correction).
 ///
 /// The input and the output are supposed to be in the [0, 1] range.
diff --git a/src/bin/rsvg-convert.rs b/src/bin/rsvg-convert.rs
index a467175a..23202cd6 100644
--- a/src/bin/rsvg-convert.rs
+++ b/src/bin/rsvg-convert.rs
@@ -309,6 +309,7 @@ impl std::fmt::Display for Output {
 }
 
 arg_enum! {
+    // Keep this enum in sync with supported_formats in parse_args()
     #[derive(Clone, Copy, Debug)]
     enum Format {
         Png,
@@ -459,6 +460,18 @@ impl Converter {
 }
 
 fn parse_args() -> Result<Converter, clap::Error> {
+    let supported_formats = vec![
+        "Png",
+        #[cfg(have_cairo_pdf)]
+        "Pdf",
+        #[cfg(have_cairo_ps)]
+        "Ps",
+        #[cfg(have_cairo_ps)]
+        "Eps",
+        #[cfg(have_cairo_svg)]
+        "Svg",
+    ];
+
     let app = clap::App::new("rsvg-convert")
         .version(concat!("version ", crate_version!()))
         .about("Convert SVG files to other image formats")
@@ -534,7 +547,7 @@ fn parse_args() -> Result<Converter, clap::Error> {
                 .short("f")
                 .long("format")
                 .takes_value(true)
-                .possible_values(&Format::variants())
+                .possible_values(supported_formats.as_slice())
                 .case_insensitive(true)
                 .default_value("png")
                 .help("Output format"),