Rollup merge of #74643 - petrochenkov:noenvrerun, r=Mark-Simulacrum

build: Remove unnecessary `cargo:rerun-if-env-changed` annotations

... and a couple of related cleanups.

rustc and cargo now track the majority of env var dependencies automatically (rust-lang/cargo#8421), so the annotations are no longer necessary.

Author: Manishearth

src/build_helper/lib.rs

@@ -1,3 +1,5 @@
+use std::ffi::{OsStr, OsString};
+use std::fmt::Display;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Stdio};
 use std::time::{SystemTime, UNIX_EPOCH};
@@ -28,6 +30,14 @@ macro_rules! t {
     };
 }
 
+/// Reads an environment variable and adds it to dependencies.
+/// Supposed to be used for all variables except those set for build scripts by cargo
+/// https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-build-scripts
+pub fn tracked_env_var_os<K: AsRef<OsStr> + Display>(key: K) -> Option<OsString> {
+    println!("cargo:rerun-if-env-changed={}", key);
+    env::var_os(key)
+}
+
 // Because Cargo adds the compiler's dylib path to our library search path, llvm-config may
 // break: the dylib path for the compiler, as of this writing, contains a copy of the LLVM
 // shared library, which means that when our freshly built llvm-config goes to load it's
@@ -37,10 +47,8 @@ macro_rules! t {
 // perfect -- we might actually want to see something from Cargo's added library paths -- but
 // for now it works.
 pub fn restore_library_path() {
-    println!("cargo:rerun-if-env-changed=REAL_LIBRARY_PATH_VAR");
-    println!("cargo:rerun-if-env-changed=REAL_LIBRARY_PATH");
-    let key = env::var_os("REAL_LIBRARY_PATH_VAR").expect("REAL_LIBRARY_PATH_VAR");
-    if let Some(env) = env::var_os("REAL_LIBRARY_PATH") {
+    let key = tracked_env_var_os("REAL_LIBRARY_PATH_VAR").expect("REAL_LIBRARY_PATH_VAR");
+    if let Some(env) = tracked_env_var_os("REAL_LIBRARY_PATH") {
         env::set_var(&key, &env);
     } else {
         env::remove_var(&key);

src/libprofiler_builtins/Cargo.toml

@@ -1,6 +1,5 @@
 [package]
 authors = ["The Rust Project Developers"]
-build = "build.rs"
 name = "profiler_builtins"
 version = "0.0.0"
 edition = "2018"

src/libprofiler_builtins/build.rs

@@ -9,6 +9,8 @@ fn main() {
     let target = env::var("TARGET").expect("TARGET was not set");
     let cfg = &mut cc::Build::new();
 
+    // FIXME: `rerun-if-changed` directives are not currently emitted and the build script
+    // will not rerun on changes in these source files or headers included into them.
     let mut profile_sources = vec![
         "GCDAProfiling.c",
         "InstrProfiling.c",

src/librustc_ast/build.rs

@@ -3,7 +3,6 @@ authors = ["The Rust Project Developers"]
 name = "rustc_attr"
 version = "0.0.0"
 edition = "2018"
-build = "build.rs"
 
 [lib]
 name = "rustc_attr"