rustbuild: don't set cxx if not configured

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

src/bootstrap/builder.rs

@@ -1135,10 +1135,12 @@ impl<'a> Builder<'a> {
                     .env(format!("RANLIB_{}", target), ranlib);
             }
 
-            let cxx = ccacheify(&self.cxx(target));
-            cargo
-                .env(format!("CXX_{}", target), &cxx)
-                .env(format!("CXXFLAGS_{}", target), cflags);
+            if let Ok(cxx) = self.cxx(target) {
+                let cxx = ccacheify(&cxx);
+                cargo
+                    .env(format!("CXX_{}", target), &cxx)
+                    .env(format!("CXXFLAGS_{}", target), cflags);
+            }
         }
 
         if (cmd == "build" || cmd == "rustc")

src/bootstrap/cc_detect.rs

@@ -102,18 +102,25 @@ pub fn find(build: &mut Build) {
         let mut cfg = cc::Build::new();
         cfg.cargo_metadata(false).opt_level(2).warnings(false).debug(false).cpp(true)
             .target(&target).host(&build.build);
-        if let Some(cxx) = config.and_then(|c| c.cxx.as_ref()) {
+
+        let cxx_configured = if let Some(cxx) = config.and_then(|c| c.cxx.as_ref()) {
             cfg.compiler(cxx);
+            true
         } else {
-            set_compiler(&mut cfg, Language::CPlusPlus, target, config, build);
+            set_compiler(&mut cfg, Language::CPlusPlus, target, config, build)
+        };
+
+        if cxx_configured {
+            let compiler = cfg.get_compiler();
+            build.cxx.insert(target, compiler);
         }
-        let compiler = cfg.get_compiler();
-        build.cxx.insert(target, compiler);
 
         build.verbose(&format!("CC_{} = {:?}", &target, build.cc(target)));
         build.verbose(&format!("CFLAGS_{} = {:?}", &target, cflags));
-        build.verbose(&format!("CXX_{} = {:?}", &target, build.cxx(target)));
-        build.verbose(&format!("CXXFLAGS_{} = {:?}", &target, cflags));
+        if let Ok(cxx) = build.cxx(target) {
+            build.verbose(&format!("CXX_{} = {:?}", &target, cxx));
+            build.verbose(&format!("CXXFLAGS_{} = {:?}", &target, cflags));
+        }
         if let Some(ar) = ar {
             build.verbose(&format!("AR_{} = {:?}", &target, ar));
             build.ar.insert(target, ar);
@@ -125,7 +132,7 @@ fn set_compiler(cfg: &mut cc::Build,
                 compiler: Language,
                 target: Interned<String>,
                 config: Option<&Target>,
-                build: &Build) {
+                build: &Build) -> bool {
     match &*target {
         // When compiling for android we may have the NDK configured in the
         // config.toml in which case we look there. Otherwise the default
@@ -138,6 +145,7 @@ fn set_compiler(cfg: &mut cc::Build,
                                    .replace("thumbv7", "arm");
                 let compiler = format!("{}-{}", target, compiler.clang());
                 cfg.compiler(ndk.join("bin").join(compiler));
+                return true;
             }
         }
 
@@ -147,32 +155,35 @@ fn set_compiler(cfg: &mut cc::Build,
             let c = cfg.get_compiler();
             let gnu_compiler = compiler.gcc();
             if !c.path().ends_with(gnu_compiler) {
-                return
+                return false;
             }
 
             let output = output(c.to_command().arg("--version"));
             let i = match output.find(" 4.") {
                 Some(i) => i,
-                None => return,
+                None => return false,
             };
             match output[i + 3..].chars().next().unwrap() {
                 '0' ..= '6' => {}
-                _ => return,
+                _ => return false,
             }
             let alternative = format!("e{}", gnu_compiler);
             if Command::new(&alternative).output().is_ok() {
                 cfg.compiler(alternative);
+                return true;
             }
         }
 
         "mips-unknown-linux-musl" => {
             if cfg.get_compiler().path().to_str() == Some("gcc") {
                 cfg.compiler("mips-linux-musl-gcc");
+                return true;
             }
         }
         "mipsel-unknown-linux-musl" => {
             if cfg.get_compiler().path().to_str() == Some("gcc") {
                 cfg.compiler("mipsel-linux-musl-gcc");
+                return true;
             }
         }
 
@@ -181,12 +192,14 @@ fn set_compiler(cfg: &mut cc::Build,
                 let guess = root.join("bin/musl-gcc");
                 if guess.exists() {
                     cfg.compiler(guess);
+                    return true;
                 }
             }
         }
 
         _ => {}
     }
+    false
 }
 
 /// The target programming language for a native compiler.

src/bootstrap/compile.rs

@@ -782,7 +782,7 @@ pub fn build_codegen_backend(builder: &Builder<'_>,
                !target.contains("windows") &&
                !target.contains("apple") {
                 let file = compiler_file(builder,
-                                         builder.cxx(target),
+                                         builder.cxx(target).unwrap(),
                                          target,
                                          "libstdc++.a");
                 cargo.env("LLVM_STATIC_STDCPP", file);

src/bootstrap/lib.rs

@@ -815,8 +815,13 @@ impl Build {
     }
 
     /// Returns the path to the C++ compiler for the target specified.
-    fn cxx(&self, target: Interned<String>) -> &Path {
-        self.cxx[&target].path()
+    fn cxx(&self, target: Interned<String>) -> Result<&Path, String> {
+        match self.cxx.get(&target) {
+            Some(p) => Ok(p.path()),
+            None => Err(format!(
+                    "target `{}` is not configured as a host, only as a target",
+                    target))
+        }
     }
 
     /// Returns the path to the linker for the given target if it needs to be overridden.

src/bootstrap/native.rs

@@ -358,7 +358,7 @@ fn configure_cmake(builder: &Builder<'_>,
 
     let (cc, cxx) = match builder.config.llvm_clang_cl {
         Some(ref cl) => (cl.as_ref(), cl.as_ref()),
-        None => (builder.cc(target), builder.cxx(target)),
+        None => (builder.cc(target), builder.cxx(target).unwrap()),
     };
 
     // Handle msvc + ninja + ccache specially (this is what the bots use)

src/bootstrap/sanity.rs

@@ -146,7 +146,7 @@ pub fn check(build: &mut Build) {
 
     for host in &build.hosts {
         if !build.config.dry_run {
-            cmd_finder.must_have(build.cxx(*host));
+            cmd_finder.must_have(build.cxx(*host).unwrap());
         }
     }
 

src/bootstrap/test.rs

@@ -1211,7 +1211,7 @@ impl Step for Compiletest {
                 cmd.arg("--cc")
                     .arg(builder.cc(target))
                     .arg("--cxx")
-                    .arg(builder.cxx(target))
+                    .arg(builder.cxx(target).unwrap())
                     .arg("--cflags")
                     .arg(builder.cflags(target, GitRepo::Rustc).join(" "))
                     .arg("--llvm-components")