Add a build option to specify the bootstrap cache

Setting the bootstrap cache path to an external location can help to
speed up builds in cases where the build directory is not kept between
builds, e.g. in CI or other automated build systems.

5 files changed, 18 insertions, 9 deletions

diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 04146eb78d7..6e49bcc9744 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -557,7 +557,9 @@ class RustBuild(object):
                 shutil.rmtree(bin_root)
 
             key = self.stage0_compiler.date
-            cache_dst = os.getenv('RUSTC_BOOTSTRAP_CACHE', os.path.join(self.build_dir, "cache"))
+            cache_dst = (self.get_toml('bootstrap-cache-path', 'build') or
+                os.path.join(self.build_dir, "cache"))
+
             rustc_cache = os.path.join(cache_dst, key)
             if not os.path.exists(rustc_cache):
                 os.makedirs(rustc_cache)
diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index 8b65e8ff9c3..4257c0f7991 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -149,6 +149,7 @@ v("default-linker", "rust.default-linker", "the default linker")
 # (others are conditionally saved).
 o("manage-submodules", "build.submodules", "let the build manage the git submodules")
 o("full-bootstrap", "build.full-bootstrap", "build three compilers instead of two (not recommended except for testing reproducible builds)")
+o("bootstrap-cache-path", "build.bootstrap-cache-path", "use provided path for the bootstrap cache")
 o("extended", "build.extended", "build an extended rust tool set")
 
 v("tools", None, "List of extended tools will be installed")
diff --git a/src/bootstrap/src/core/config/config.rs b/src/bootstrap/src/core/config/config.rs
index 875a4efae02..326f8f57173 100644
--- a/src/bootstrap/src/core/config/config.rs
+++ b/src/bootstrap/src/core/config/config.rs
@@ -161,6 +161,7 @@ pub struct Config {
     pub vendor: bool,
     pub target_config: HashMap<TargetSelection, Target>,
     pub full_bootstrap: bool,
+    pub bootstrap_cache_path: Option<PathBuf>,
     pub extended: bool,
     pub tools: Option<HashSet<String>>,
     pub sanitizers: bool,
@@ -827,6 +828,7 @@ define_config! {
         locked_deps: Option<bool> = "locked-deps",
         vendor: Option<bool> = "vendor",
         full_bootstrap: Option<bool> = "full-bootstrap",
+        bootstrap_cache_path: Option<PathBuf> = "bootstrap-cache-path",
         extended: Option<bool> = "extended",
         tools: Option<HashSet<String>> = "tools",
         verbose: Option<usize> = "verbose",
@@ -1389,6 +1391,7 @@ impl Config {
             locked_deps,
             vendor,
             full_bootstrap,
+            bootstrap_cache_path,
             extended,
             tools,
             verbose,
@@ -1477,6 +1480,7 @@ impl Config {
         config.reuse = reuse.map(PathBuf::from);
         config.submodules = submodules;
         config.android_ndk = android_ndk;
+        config.bootstrap_cache_path = bootstrap_cache_path;
         set(&mut config.low_priority, low_priority);
         set(&mut config.compiler_docs, compiler_docs);
         set(&mut config.library_docs_private_items, library_docs_private_items);
diff --git a/src/bootstrap/src/core/download.rs b/src/bootstrap/src/core/download.rs
index db83d8a214f..27829eab937 100644
--- a/src/bootstrap/src/core/download.rs
+++ b/src/bootstrap/src/core/download.rs
@@ -578,10 +578,8 @@ impl Config {
             return;
         }
 
-        let cache_dst = match env::var_os("RUSTC_BOOTSTRAP_CACHE") {
-            Some(v) => PathBuf::from(v),
-            None => self.out.join("cache"),
-        };
+        let cache_dst =
+            self.bootstrap_cache_path.as_ref().cloned().unwrap_or_else(|| self.out.join("cache"));
 
         let cache_dir = cache_dst.join(key);
         if !cache_dir.exists() {
@@ -709,10 +707,9 @@ download-rustc = false
         let llvm_assertions = self.llvm_assertions;
 
         let cache_prefix = format!("llvm-{llvm_sha}-{llvm_assertions}");
-        let cache_dst = match env::var_os("RUSTC_BOOTSTRAP_CACHE") {
-            Some(v) => PathBuf::from(v),
-            None => self.out.join("cache"),
-        };
+        let cache_dst =
+            self.bootstrap_cache_path.as_ref().cloned().unwrap_or_else(|| self.out.join("cache"));
+
         let rustc_cache = cache_dst.join(cache_prefix);
         if !rustc_cache.exists() {
             t!(fs::create_dir_all(&rustc_cache));
diff --git a/src/bootstrap/src/utils/change_tracker.rs b/src/bootstrap/src/utils/change_tracker.rs
index 9a50ad4437e..5ff367ea3ad 100644
--- a/src/bootstrap/src/utils/change_tracker.rs
+++ b/src/bootstrap/src/utils/change_tracker.rs
@@ -136,4 +136,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Info,
         summary: "`x install` now skips providing tarball sources (under 'build/dist' path) to speed up the installation process.",
     },
+    ChangeInfo {
+        change_id: 121976,
+        severity: ChangeSeverity::Info,
+        summary: "A new `boostrap-cache-path` option has been introduced. Set it in your config.toml to use a different path for the download cache.",
+    },
 ];