add dlopen Cargo feature using dlib to load fontconfig at runtime

Fixes yeslogic#11

.travis.yml

@@ -13,7 +13,7 @@ rust:
   - nightly
   - beta
   - stable
-  - 1.38.0
+  - 1.46.0
 
 jobs:
   allow_failures:
@@ -24,3 +24,4 @@ before_install:
 
 script:
   - cargo test
+  - RUST_FONTCONFIG_DLOPEN=on cargo test

Cargo.toml

@@ -2,4 +2,4 @@
 members = [
     "fontconfig-sys",
     "fontconfig"
-]
+]

fontconfig-sys/Cargo.toml

@@ -1,6 +1,8 @@
 [package]
 name = "yeslogic-fontconfig-sys"
-version = "2.11.2"
+version = "3.0.0"
+edition = "2018"
+rust-version = "1.46"
 authors = [
     "Austin Bonander <[email protected]>",
     "The Servo Project Developers",
@@ -16,7 +18,6 @@ homepage = "https://github.com/yeslogic/fontconfig-rs"
 documentation = "https://docs.rs/crate/yeslogic-fontconfig-sys"
 repository = "https://github.com/yeslogic/fontconfig-rs"
 
-build = "build.rs"
 links = "fontconfig"
 
 [badges]
@@ -27,6 +28,13 @@ name = "fontconfig_sys"
 
 [dependencies]
 const-cstr = "0.3"
+dlib = "0.5.0"
+# This cannot be optional because build.rs can't conditionally enable it
+# when the RUST_FONTCONFIG_DLOPEN environment variable is set.
+lazy_static = "1.4.0"
+
+[features]
+dlopen = []
 
 [build-dependencies]
 pkg-config = "0.3"

fontconfig-sys/build.rs

@@ -1,5 +1,11 @@
 extern crate pkg_config;
 
 fn main() {
-    pkg_config::find_library("fontconfig").unwrap();
+    let dlopen = std::env::var("RUST_FONTCONFIG_DLOPEN").is_ok();
+    if dlopen {
+        println!("cargo:rustc-cfg=feature=\"dlopen\"");
+    }
+    if !(dlopen || cfg!(feature = "dlopen")) {
+        pkg_config::find_library("fontconfig").unwrap();
+    }
 }