Ability to collect Cargo directives instead of printing them directly

Author: kornelski

src/lib.rs

@@ -89,12 +89,14 @@ use std::env;
 use std::error;
 use std::ffi::{OsStr, OsString};
 use std::fmt;
+use std::fmt::Arguments;
 use std::fmt::Display;
 use std::io;
 use std::ops::{Bound, RangeBounds};
 use std::path::PathBuf;
 use std::process::{Command, Output};
 use std::str;
+use std::sync::Mutex;
 
 /// Wrapper struct to polyfill methods introduced in 1.57 (`get_envs`, `get_args` etc).
 /// This is needed to reconstruct the pkg-config command for output in a copy-
@@ -106,7 +108,7 @@ struct WrappedCommand {
     args: Vec<OsString>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Debug)]
 pub struct Config {
     statik: Option<bool>,
     min_version: Bound<String>,
@@ -116,6 +118,24 @@ pub struct Config {
     env_metadata: bool,
     print_system_libs: bool,
     print_system_cflags: bool,
+    /// If `Some`, cargo directives will be buffered instead of being printed directly
+    metadata_buffer: Option<Mutex<Vec<String>>>,
+}
+
+impl Clone for Config {
+    fn clone(&self) -> Config {
+        Config {
+            statik: self.statik,
+            min_version: self.min_version.clone(),
+            max_version: self.max_version.clone(),
+            extra_args: self.extra_args.clone(),
+            print_system_cflags: self.print_system_cflags,
+            print_system_libs: self.print_system_libs,
+            cargo_metadata: self.cargo_metadata,
+            env_metadata: self.env_metadata,
+            metadata_buffer: None,
+        }
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -463,6 +483,16 @@ impl Config {
             print_system_libs: true,
             cargo_metadata: true,
             env_metadata: true,
+            metadata_buffer: None,
+        }
+    }
+
+    /// Emit buffered metadata, if any
+    fn print_bufferred(&self) {
+        if let Some(mut buf) = self.metadata_buffer.as_ref().and_then(|m| m.lock().ok()) {
+            for line in buf.drain(..) {
+                println!("cargo:{}", line);
+            }
         }
     }
 
@@ -643,11 +673,19 @@ impl Config {
 
     fn env_var_os(&self, name: &str) -> Option<OsString> {
         if self.env_metadata {
-            println!("cargo:rerun-if-env-changed={}", name);
+            self.emit_cargo_directive(format_args!("rerun-if-env-changed={}", name));
         }
         env::var_os(name)
     }
 
+    fn emit_cargo_directive(&self, fmt: Arguments) {
+        if let Some(mut buf) = self.metadata_buffer.as_ref().and_then(|m| m.lock().ok()) {
+            buf.push(fmt.to_string());
+        } else {
+            println!("cargo:{}", fmt);
+        }
+    }
+
     fn is_static(&self, name: &str) -> bool {
         self.statik.unwrap_or_else(|| self.infer_static(name))
     }
@@ -733,7 +771,7 @@ impl Config {
 
     fn print_metadata(&self, s: &str) {
         if self.cargo_metadata {
-            println!("cargo:{}", s);
+            self.emit_cargo_directive(format_args!("{}", s));
         }
     }
 
@@ -765,6 +803,7 @@ impl Default for Config {
             print_system_libs: false,
             cargo_metadata: false,
             env_metadata: false,
+            metadata_buffer: None,
         }
     }
 }