test: show that -Awarnings fails target info probing

This will be resolved in the next commit

.github/workflows/main.yml

@@ -161,6 +161,7 @@ jobs:
     - run: rustup update --no-self-update stable
     - run: rustup update --no-self-update ${{ matrix.rust }} && rustup default ${{ matrix.rust }}
     - run: rustup target add ${{ matrix.other }}
+    - run: rustup target add wasm32-unknown-unknown
     - run: rustup target add aarch64-unknown-none # need this for build-std mock tests
       if: startsWith(matrix.rust, 'nightly')
     - run: rustup component add rustc-dev llvm-tools-preview rust-docs
@@ -225,6 +226,7 @@ jobs:
       - uses: actions/checkout@v4
       - run: rustup update --no-self-update stable && rustup default stable
       - run: rustup target add i686-unknown-linux-gnu
+      - run: rustup target add wasm32-unknown-unknown
       - run: sudo apt update -y && sudo apt install gcc-multilib libsecret-1-0 libsecret-1-dev -y
       - run: rustup component add rustfmt || echo "rustfmt not available"
       - run: cargo test -p cargo

tests/testsuite/cross_compile.rs

@@ -1260,3 +1260,38 @@ fn doctest_xcompile_linker() {
 "#]])
         .run();
 }
+
+#[cargo_test]
+fn always_emit_warnings_as_warnings_when_learning_target_info() {
+    if cross_compile::disabled() {
+        return;
+    }
+
+    let target = "wasm32-unknown-unknown";
+    if !cross_compile::requires_target_installed(target) {
+        return;
+    }
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                edition = "2015"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build -v --target")
+        .env("RUSTFLAGS", "-Awarnings")
+        .arg(target)
+        .with_status(101)
+        .with_stderr_data(str![[r#"
+[ERROR] output of --print=file-names missing when learning about target-specific information from rustc
+command was: `rustc - --crate-name ___ --print=file-names -Awarnings --target wasm32-unknown-unknown --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro --print=sysroot --print=split-debuginfo --print=crate-name --print=cfg`
+...
+"#]])
+        .run();
+}