Auto merge of #13560 - heisen-li:build_flag, r=weihanglo

[fix]:Build script not rerun when target rustflags change

### What does this PR try to resolve?

Fixes #13003

src/cargo/core/compiler/fingerprint/mod.rs

@@ -1526,11 +1526,14 @@ See https://doc.rust-lang.org/cargo/reference/build-scripts.html#rerun-if-change
             .collect::<CargoResult<Vec<_>>>()?
     };
 
+    let rustflags = build_runner.bcx.rustflags_args(unit).to_vec();
+
     Ok(Fingerprint {
         local: Mutex::new(local),
         rustc: util::hash_u64(&build_runner.bcx.rustc().verbose_version),
         deps,
         outputs: if overridden { Vec::new() } else { vec![output] },
+        rustflags,
 
         // Most of the other info is blank here as we don't really include it
         // in the execution of the build script, but... this may be a latent

tests/testsuite/build_script.rs

@@ -5537,3 +5537,60 @@ fn test_old_syntax_with_old_msrv() {
     p.cargo("build -v").run();
     p.cargo("run -v").with_stdout("foo\n").run();
 }
+
+#[cargo_test]
+fn build_script_rerun_when_target_rustflags_change() {
+    let target = rustc_host();
+    let p = project()
+        .file(
+            "src/main.rs",
+            r#"
+            fn main() {
+                #[cfg(enable)]
+                println!("hello");
+            }
+            "#,
+        )
+        .file(
+            "build.rs",
+            r#"
+            use std::env;
+
+            fn main() {
+                if let Ok(rustflags) = env::var("CARGO_ENCODED_RUSTFLAGS") {
+                    if !rustflags.is_empty() {
+                        println!("cargo::rustc-cfg=enable")
+                    }
+                }
+            }
+            "#,
+        )
+        .build();
+
+    p.cargo("run --target")
+        .arg(&target)
+        .with_stderr(
+            "\
+[COMPILING] foo v0.0.1 ([..])
+[FINISHED] [..]
+[RUNNING] [..]
+",
+        )
+        .run();
+
+    p.cargo("run --target")
+        .arg(&target)
+        .env("RUSTFLAGS", "-C opt-level=3")
+        .with_stderr(
+            "\
+[COMPILING] foo v0.0.1 ([..])
+[FINISHED] [..]
+[RUNNING] [..]
+",
+        )
+        .with_stdout(
+            "\
+hello",
+        )
+        .run();
+}