Allow cross-compilation if pkg-config is customized

src/lib.rs

@@ -64,6 +64,7 @@
 #![doc(html_root_url = "https://docs.rs/pkg-config/0.3")]
 
 #[allow(unused_imports)] // Required for Rust <1.23
+#[allow(deprecated)]
 use std::ascii::AsciiExt;
 use std::collections::HashMap;
 use std::env;
@@ -76,15 +77,6 @@ use std::path::{PathBuf, Path};
 use std::process::{Command, Output};
 use std::str;
 
-pub fn target_supported() -> bool {
-    let target = env::var("TARGET").unwrap_or_else(|_| String::new());
-    let host = env::var("HOST").unwrap_or_else(|_| String::new());
-
-    // Only use pkg-config in host == target situations by default (allowing an
-    // override).
-    (host == target || env::var_os("PKG_CONFIG_ALLOW_CROSS").is_some())
-}
-
 #[derive(Clone)]
 pub struct Config {
     statik: Option<bool>,
@@ -310,7 +302,7 @@ impl Config {
         let abort_var_name = format!("{}_NO_PKG_CONFIG", envify(name));
         if self.env_var_os(&abort_var_name).is_some() {
             return Err(Error::EnvNoPkgConfig(abort_var_name))
-        } else if !target_supported() {
+        } else if !self.target_supported() {
             return Err(Error::CrossCompilation);
         }
 
@@ -325,6 +317,31 @@ impl Config {
         Ok(library)
     }
 
+    pub fn target_supported(&self) -> bool {
+        let target = env::var("TARGET").unwrap_or_default();
+        let host = env::var("HOST").unwrap_or_default();
+
+        // Only use pkg-config in host == target situations by default (allowing an
+        // override).
+        if host == target {
+            return true;
+        }
+
+        // pkg-config may not be aware of cross-compilation, and require
+        // a wrapper script that sets up platform-specific prefixes.
+        match self.targetted_env_var("PKG_CONFIG_ALLOW_CROSS") {
+            // don't use pkg-config if explicitly disabled
+            Ok(ref val) if val == "0" => false,
+            Ok(_) => true,
+            Err(_) => {
+                // if not disabled, and pkg-config is customized,
+                // then assume it's prepared for cross-compilation
+                self.targetted_env_var("PKG_CONFIG").is_ok() ||
+                self.targetted_env_var("PKG_CONFIG_SYSROOT_DIR").is_ok()
+            },
+        }
+    }
+
     /// Deprecated in favor of the top level `get_variable` function
     #[doc(hidden)]
     pub fn get_variable(package: &str, variable: &str) -> Result<String, String> {

tests/test.rs

@@ -16,6 +16,7 @@ fn reset() {
         if k.contains("DYNAMIC") ||
            k.contains("STATIC") ||
            k.contains("PKG_CONFIG_ALLOW_CROSS") ||
+           k.contains("PKG_CONFIG_SYSROOT_DIR") ||
            k.contains("FOO_NO_PKG_CONFIG") {
             env::remove_var(&k);
         }
@@ -51,6 +52,30 @@ fn cross_enabled() {
     find("foo").unwrap();
 }
 
+#[test]
+fn cross_enabled_if_customized() {
+    let _g = LOCK.lock();
+    reset();
+    env::set_var("TARGET", "foo");
+    env::set_var("HOST", "bar");
+    env::set_var("PKG_CONFIG_SYSROOT_DIR", "/tmp/cross-test");
+    find("foo").unwrap();
+}
+
+#[test]
+fn cross_disabled_if_customized() {
+    let _g = LOCK.lock();
+    reset();
+    env::set_var("TARGET", "foo");
+    env::set_var("HOST", "bar");
+    env::set_var("PKG_CONFIG_ALLOW_CROSS", "0");
+    env::set_var("PKG_CONFIG_SYSROOT_DIR", "/tmp/cross-test");
+    match find("foo") {
+        Err(Error::CrossCompilation) => {},
+        _ => panic!("expected CrossCompilation failure"),
+    }
+}
+
 #[test]
 fn package_disabled() {
     let _g = LOCK.lock();