bootstrap: add std_features config

bootstrap: add std_features  to config.example

fix: use BTreeSet for std-features; add unit tests

* fix formatting of string in front of std_features
* rename `std_features` to `std-features` in config.toml

fix: remove space before std-features in config.toml

fix: remove explicit .into_iter conversion

bootstrap: add details for rust.std-features in config.example.toml

Co-authored-by: Onur Özkan <onurozkan.dev@outlook.com>

fix: remove `Option<T>` from `rust_std_features`

fix: move default rust_std_features to config

fix: make std_features CI rustc incompatible

Author: shrirambalaji

Diff for: config.example.toml

@@ -759,6 +759,16 @@
 # Build compiler with the optimization enabled and -Zvalidate-mir, currently only for `std`
 #validate-mir-opts = 3
 
+# Configure `std` features used during bootstrap.
+# Default features will be expanded in the following cases:
+#  - If `rust.llvm-libunwind` or `target.llvm-libunwind` is enabled:
+#    - "llvm-libunwind" will be added for in-tree LLVM builds.
+#    - "system-llvm-libunwind" will be added for system LLVM builds.
+#  - If `rust.backtrace` is enabled, "backtrace" will be added.
+#  - If `rust.profiler` or `target.profiler` is enabled, "profiler" will be added.
+#  - If building for a zkvm target, "compiler-builtins-mem" will be added.
+#std-features = ["panic_unwind"]
+
 # =============================================================================
 # Options for specific targets
 #

Diff for: src/bootstrap/src/core/config/config.rs

@@ -4,7 +4,7 @@
 //! how the build runs.
 
 use std::cell::{Cell, RefCell};
-use std::collections::{HashMap, HashSet};
+use std::collections::{BTreeSet, HashMap, HashSet};
 use std::fmt::{self, Display};
 use std::io::IsTerminal;
 use std::path::{absolute, Path, PathBuf};
@@ -287,6 +287,7 @@ pub struct Config {
     pub rust_profile_generate: Option<String>,
     pub rust_lto: RustcLto,
     pub rust_validate_mir_opts: Option<u32>,
+    pub rust_std_features: BTreeSet<String>,
     pub llvm_profile_use: Option<String>,
     pub llvm_profile_generate: bool,
     pub llvm_libunwind_default: Option<LlvmLibunwind>,
@@ -1141,6 +1142,7 @@ define_config! {
         download_rustc: Option<StringOrBool> = "download-rustc",
         lto: Option<String> = "lto",
         validate_mir_opts: Option<u32> = "validate-mir-opts",
+        std_features: Option<BTreeSet<String>> = "std-features",
     }
 }
 
@@ -1634,6 +1636,7 @@ impl Config {
         let mut optimize = None;
         let mut omit_git_hash = None;
         let mut lld_enabled = None;
+        let mut std_features = None;
 
         let mut is_user_configured_rust_channel = false;
 
@@ -1692,6 +1695,7 @@ impl Config {
                 stack_protector,
                 strip,
                 lld_mode,
+                std_features: std_features_toml,
             } = rust;
 
             is_user_configured_rust_channel = channel.is_some();
@@ -1711,6 +1715,7 @@ impl Config {
             debuginfo_level_tools = debuginfo_level_tools_toml;
             debuginfo_level_tests = debuginfo_level_tests_toml;
             lld_enabled = lld_enabled_toml;
+            std_features = std_features_toml;
 
             optimize = optimize_toml;
             omit_git_hash = omit_git_hash_toml;
@@ -2091,6 +2096,9 @@ impl Config {
             );
         }
 
+        let default_std_features = BTreeSet::from([String::from("panic-unwind")]);
+        config.rust_std_features = std_features.unwrap_or(default_std_features);
+
         let default = debug == Some(true);
         config.rust_debug_assertions = debug_assertions.unwrap_or(default);
         config.rust_debug_assertions_std =
@@ -2990,6 +2998,7 @@ fn check_incompatible_options_for_ci_rustc(
         description,
         incremental,
         default_linker,
+        std_features,
 
         // Rest of the options can simply be ignored.
         debug: _,
@@ -3051,6 +3060,7 @@ fn check_incompatible_options_for_ci_rustc(
     err!(current_rust_config.default_linker, default_linker);
     err!(current_rust_config.stack_protector, stack_protector);
     err!(current_rust_config.lto, lto);
+    err!(current_rust_config.std_features, std_features);
 
     warn!(current_rust_config.channel, channel);
     warn!(current_rust_config.description, description);

Diff for: src/bootstrap/src/core/config/tests.rs

@@ -1,3 +1,4 @@
+use std::collections::BTreeSet;
 use std::env;
 use std::fs::{remove_file, File};
 use std::io::Write;
@@ -326,3 +327,24 @@ fn verbose_tests_default_value() {
     let config = Config::parse(Flags::parse(&["build".into(), "compiler".into(), "-v".into()]));
     assert_eq!(config.verbose_tests, true);
 }
+
+#[test]
+fn parse_rust_std_features() {
+    let config = parse("rust.std-features = [\"panic-unwind\", \"backtrace\"]");
+    let expected_features: BTreeSet<String> =
+        ["panic-unwind", "backtrace"].into_iter().map(|s| s.to_string()).collect();
+    assert_eq!(config.rust_std_features, expected_features);
+}
+
+#[test]
+fn parse_rust_std_features_empty() {
+    let config = parse("rust.std-features = []");
+    let expected_features: BTreeSet<String> = BTreeSet::new();
+    assert_eq!(config.rust_std_features, expected_features);
+}
+
+#[test]
+#[should_panic]
+fn parse_rust_std_features_invalid() {
+    parse("rust.std-features = \"backtrace\"");
+}

Diff for: src/bootstrap/src/lib.rs

@@ -17,7 +17,7 @@
 //! also check out the `src/bootstrap/README.md` file for more information.
 
 use std::cell::{Cell, RefCell};
-use std::collections::{HashMap, HashSet};
+use std::collections::{BTreeSet, HashMap, HashSet};
 use std::fmt::Display;
 use std::fs::{self, File};
 use std::path::{Path, PathBuf};
@@ -661,28 +661,31 @@ impl Build {
         &self.config.rust_info
     }
 
-    /// Gets the space-separated set of activated features for the standard
-    /// library.
+    /// Gets the space-separated set of activated features for the standard library.
+    /// This can be configured with the `std-features` key in config.toml.
     fn std_features(&self, target: TargetSelection) -> String {
-        let mut features = " panic-unwind".to_string();
+        let mut features: BTreeSet<&str> =
+            self.config.rust_std_features.iter().map(|s| s.as_str()).collect();
 
         match self.config.llvm_libunwind(target) {
-            LlvmLibunwind::InTree => features.push_str(" llvm-libunwind"),
-            LlvmLibunwind::System => features.push_str(" system-llvm-libunwind"),
-            LlvmLibunwind::No => {}
-        }
+            LlvmLibunwind::InTree => features.insert("llvm-libunwind"),
+            LlvmLibunwind::System => features.insert("system-llvm-libunwind"),
+            LlvmLibunwind::No => false,
+        };
+
         if self.config.backtrace {
-            features.push_str(" backtrace");
+            features.insert("backtrace");
         }
         if self.config.profiler_enabled(target) {
-            features.push_str(" profiler");
+            features.insert("profiler");
         }
         // Generate memcpy, etc.  FIXME: Remove this once compiler-builtins
         // automatically detects this target.
         if target.contains("zkvm") {
-            features.push_str(" compiler-builtins-mem");
+            features.insert("compiler-builtins-mem");
         }
-        features
+
+        features.into_iter().collect::<Vec<_>>().join(" ")
     }
 
     /// Gets the space-separated set of activated features for the compiler.