wip: Document heuristics and disable them for libdir, if cross compiling

Author: amyspark

src/build.rs

@@ -1043,15 +1043,15 @@ pub fn cbuild(
 ) -> anyhow::Result<(Vec<CPackage>, CompileOptions)> {
     let rustc = config.load_global_rustc(Some(ws))?;
     let targets = args.targets()?;
-    let target = match targets.len() {
-        0 => rustc.host.to_string(),
-        1 => targets[0].to_string(),
+    let (target, is_target_overridden) = match targets.len() {
+        0 => (rustc.host.to_string(), false),
+        1 => (targets[0].to_string(), true),
         _ => {
             anyhow::bail!("Multiple targets not supported yet");
         }
     };
 
-    let rustc_target = target::Target::new(&target)?;
+    let rustc_target = target::Target::new(&target, is_target_overridden)?;
 
     let default_kind = || match (rustc_target.os.as_str(), rustc_target.env.as_str()) {
         ("none", _) | (_, "musl") => vec!["staticlib"],

src/cli.rs

@@ -20,25 +20,35 @@ struct Common {
     /// `bindir`, `datarootdir`, `includedir`, `libdir`
     ///
     /// If they are absolute the prefix is ignored.
+    /// 
+    /// [default = c:/ if Windows, /boot/system/non-packaged if Haiku, else /usr/local]
     #[clap(long = "prefix")]
-    prefix: PathBuf,
+    prefix: Option<PathBuf>,
     /// Path to directory for installing generated library files
+    /// 
+    /// [default = {prefix}/bin if Windows, {prefix}/lib/{target} if Debian and target is not set manually, else {prefix}/lib]
     #[clap(long = "libdir")]
-    libdir: PathBuf,
+    libdir: Option<PathBuf>,
     /// Path to directory for installing generated headers files
+    /// 
+    /// [default = {prefix}/include]
     #[clap(long = "includedir")]
-    includedir: PathBuf,
+    includedir: Option<PathBuf>,
     /// Path to directory for installing generated executable files
-    #[clap(long = "bindir", default_value = "bin")]
-    bindir: PathBuf,
+    /// 
+    /// [default = {prefix}/bin]
+    #[clap(long = "bindir")]
+    bindir: Option<PathBuf>,
     /// Path to directory for installing generated pkg-config .pc files
     ///
     /// [default: {libdir}/pkgconfig]
     #[clap(long = "pkgconfigdir")]
     pkgconfigdir: Option<PathBuf>,
     /// Path to directory for installing read-only data
+    /// 
+    /// [default = {prefix}/data if Haiku, else {prefix}/share]
     #[clap(long = "datarootdir")]
-    datarootdir: PathBuf,
+    datarootdir: Option<PathBuf>,
     /// Path to directory for installing read-only application-specific data
     ///
     /// [default: {datarootdir}]

src/target.rs

@@ -11,14 +11,15 @@ use crate::build::CApiConfig;
 /// It uses internally `rustc` to validate the string.
 #[derive(Clone, Debug)]
 pub struct Target {
+    pub is_target_overridden: bool,
     pub arch: String,
     // pub vendor: String,
     pub os: String,
     pub env: String,
 }
 
 impl Target {
-    pub fn new<T: AsRef<std::ffi::OsStr>>(target: T) -> Result<Self, anyhow::Error> {
+    pub fn new<T: AsRef<std::ffi::OsStr>>(target: T, is_target_overridden: bool) -> Result<Self, anyhow::Error> {
         let rustc = std::env::var("RUSTC").unwrap_or_else(|_| "rustc".into());
         let mut cmd = std::process::Command::new(rustc);
 
@@ -45,6 +46,7 @@ impl Target {
                 // vendor: match_re(vendor_re, s),
                 os: match_re(os_re, s),
                 env: match_re(env_re, s),
+                is_target_overridden,
             })
         } else {
             Err(anyhow!("Cannot run {:?}", cmd))
@@ -134,32 +136,35 @@ impl Target {
     }
 
     pub fn default_libdir(&self) -> PathBuf {
-        if self.is_debianlike() {
-            let pc = std::process::Command::new("dpkg-architecture")
-                .arg("-qDEB_HOST_MULTIARCH")
-                .output();
-            match pc {
-                std::io::Result::Ok(v) => {
-                    if v.status.success() {
-                        let archpath = String::from_utf8_lossy(&v.stdout);
-                        return format!("lib/{archpath}").into();
+        if self.is_target_overridden {
+            if self.is_debianlike() {
+                let pc = std::process::Command::new("dpkg-architecture")
+                    .arg("-qDEB_HOST_MULTIARCH")
+                    .output();
+                match pc {
+                    std::io::Result::Ok(v) => {
+                        if v.status.success() {
+                            let archpath = String::from_utf8_lossy(&v.stdout);
+                            return format!("lib/{archpath}").into();
+                        }
                     }
+                    std::io::Result::Err(_) => {}
                 }
-                std::io::Result::Err(_) => {}
             }
-        }
 
-        if self.is_freebsd() {
-            return "lib".into();
-        }
-        if consts::ARCH.eq_ignore_ascii_case(&self.arch)
-            && consts::OS.eq_ignore_ascii_case(&self.os)
-        {
-            let usr_lib64 = PathBuf::from("/usr/lib64");
-            if usr_lib64.exists() && !usr_lib64.is_symlink() {
-                return "lib64".into();
+            if self.is_freebsd() {
+                return "lib".into();
+            }
+            if consts::ARCH.eq_ignore_ascii_case(&self.arch)
+                && consts::OS.eq_ignore_ascii_case(&self.os)
+            {
+                let usr_lib64 = PathBuf::from("/usr/lib64");
+                if usr_lib64.exists() && !usr_lib64.is_symlink() {
+                    return "lib64".into();
+                }
             }
         }
+
         "lib".into()
     }