feat(config): Add ChangeId enum for suppressing warnings

Introduces the `ChangeId` enum to allow suppressing `change_id` warnings.
Now, `ChangeId` supports both numeric values and the string literal `"ignore"`.
Numeric values behave as expected, while `"ignore"` is used to suppress warning messages.

src/bootstrap/src/bin/main.rs

@@ -11,8 +11,8 @@ use std::str::FromStr;
 use std::{env, process};
 
 use bootstrap::{
-    Build, CONFIG_CHANGE_HISTORY, Config, Flags, Subcommand, debug, find_recent_config_change_ids,
-    human_readable_changes, t,
+    Build, CONFIG_CHANGE_HISTORY, ChangeId, Config, Flags, Subcommand, debug,
+    find_recent_config_change_ids, human_readable_changes, t,
 };
 #[cfg(feature = "tracing")]
 use tracing::instrument;
@@ -155,51 +155,53 @@ fn check_version(config: &Config) -> Option<String> {
     let latest_change_id = CONFIG_CHANGE_HISTORY.last().unwrap().change_id;
     let warned_id_path = config.out.join("bootstrap").join(".last-warned-change-id");
 
-    if let Some(mut id) = config.change_id {
-        if id == latest_change_id {
-            return None;
+    let mut id = match config.change_id {
+        Some(ChangeId::Id(id)) if id == latest_change_id => return None,
+        Some(ChangeId::Ignore) => return None,
+        Some(ChangeId::Id(id)) => id,
+        None => {
+            msg.push_str("WARNING: The `change-id` is missing in the `bootstrap.toml`. This means that you will not be able to track the major changes made to the bootstrap configurations.\n");
+            msg.push_str("NOTE: to silence this warning, ");
+            msg.push_str(&format!(
+                "add `change-id = {latest_change_id}` at the top of `bootstrap.toml`"
+            ));
+            return Some(msg);
         }
-
-        // Always try to use `change-id` from .last-warned-change-id first. If it doesn't exist,
-        // then use the one from the bootstrap.toml. This way we never show the same warnings
-        // more than once.
-        if let Ok(t) = fs::read_to_string(&warned_id_path) {
-            let last_warned_id = usize::from_str(&t)
-                .unwrap_or_else(|_| panic!("{} is corrupted.", warned_id_path.display()));
-
-            // We only use the last_warned_id if it exists in `CONFIG_CHANGE_HISTORY`.
-            // Otherwise, we may retrieve all the changes if it's not the highest value.
-            // For better understanding, refer to `change_tracker::find_recent_config_change_ids`.
-            if CONFIG_CHANGE_HISTORY.iter().any(|config| config.change_id == last_warned_id) {
-                id = last_warned_id;
-            }
-        };
-
-        let changes = find_recent_config_change_ids(id);
-
-        if changes.is_empty() {
-            return None;
-        }
-
-        msg.push_str("There have been changes to x.py since you last updated:\n");
-        msg.push_str(&human_readable_changes(&changes));
-
-        msg.push_str("NOTE: to silence this warning, ");
-        msg.push_str(&format!(
-            "update `bootstrap.toml` to use `change-id = {latest_change_id}` instead"
-        ));
-
-        if io::stdout().is_terminal() {
-            t!(fs::write(warned_id_path, latest_change_id.to_string()));
-        }
-    } else {
-        msg.push_str("WARNING: The `change-id` is missing in the `bootstrap.toml`. This means that you will not be able to track the major changes made to the bootstrap configurations.\n");
-        msg.push_str("NOTE: to silence this warning, ");
-        msg.push_str(&format!(
-            "add `change-id = {latest_change_id}` at the top of `bootstrap.toml`"
-        ));
     };
 
+    // Always try to use `change-id` from .last-warned-change-id first. If it doesn't exist,
+    // then use the one from the bootstrap.toml. This way we never show the same warnings
+    // more than once.
+    if let Ok(t) = fs::read_to_string(&warned_id_path) {
+        let last_warned_id = usize::from_str(&t)
+            .unwrap_or_else(|_| panic!("{} is corrupted.", warned_id_path.display()));
+
+        // We only use the last_warned_id if it exists in `CONFIG_CHANGE_HISTORY`.
+        // Otherwise, we may retrieve all the changes if it's not the highest value.
+        // For better understanding, refer to `change_tracker::find_recent_config_change_ids`.
+        if CONFIG_CHANGE_HISTORY.iter().any(|config| config.change_id == last_warned_id) {
+            id = last_warned_id;
+        }
+    };
+
+    let changes = find_recent_config_change_ids(id);
+
+    if changes.is_empty() {
+        return None;
+    }
+
+    msg.push_str("There have been changes to x.py since you last updated:\n");
+    msg.push_str(&human_readable_changes(&changes));
+
+    msg.push_str("NOTE: to silence this warning, ");
+    msg.push_str(&format!(
+        "update `bootstrap.toml` to use `change-id = {latest_change_id}` instead"
+    ));
+
+    if io::stdout().is_terminal() {
+        t!(fs::write(warned_id_path, latest_change_id.to_string()));
+    }
+
     Some(msg)
 }
 

src/bootstrap/src/core/config/config.rs

@@ -193,7 +193,7 @@ pub enum GccCiMode {
 /// `bootstrap.example.toml`.
 #[derive(Default, Clone)]
 pub struct Config {
-    pub change_id: Option<usize>,
+    pub change_id: Option<ChangeId>,
     pub bypass_bootstrap_lock: bool,
     pub ccache: Option<String>,
     /// Call Build::ninja() instead of this.
@@ -700,14 +700,32 @@ pub(crate) struct TomlConfig {
     profile: Option<String>,
 }
 
+/// This enum is used for deserializing change IDs from TOML, allowing both numeric values and the string `"ignore"`.
+#[derive(Clone, Debug, PartialEq)]
+pub enum ChangeId {
+    Ignore,
+    Id(usize),
+}
+
 /// Since we use `#[serde(deny_unknown_fields)]` on `TomlConfig`, we need a wrapper type
 /// for the "change-id" field to parse it even if other fields are invalid. This ensures
 /// that if deserialization fails due to other fields, we can still provide the changelogs
 /// to allow developers to potentially find the reason for the failure in the logs..
 #[derive(Deserialize, Default)]
 pub(crate) struct ChangeIdWrapper {
-    #[serde(alias = "change-id")]
-    pub(crate) inner: Option<usize>,
+    #[serde(alias = "change-id", default, deserialize_with = "deserialize_change_id")]
+    pub(crate) inner: Option<ChangeId>,
+}
+
+fn deserialize_change_id<'de, D: Deserializer<'de>>(
+    deserializer: D,
+) -> Result<Option<ChangeId>, D::Error> {
+    let value = toml::Value::deserialize(deserializer)?;
+    Ok(match value {
+        toml::Value::String(s) if s == "ignore" => Some(ChangeId::Ignore),
+        toml::Value::Integer(i) => Some(ChangeId::Id(i as usize)),
+        _ => return Err(serde::de::Error::custom("expected \"ignore\" or an integer")),
+    })
 }
 
 /// Describes how to handle conflicts in merging two [`TomlConfig`]
@@ -1351,10 +1369,11 @@ impl Config {
         toml::from_str(&contents)
             .and_then(|table: toml::Value| TomlConfig::deserialize(table))
             .inspect_err(|_| {
-                if let Ok(Some(changes)) = toml::from_str(&contents)
-                    .and_then(|table: toml::Value| ChangeIdWrapper::deserialize(table))
-                    .map(|change_id| change_id.inner.map(crate::find_recent_config_change_ids))
+                if let Ok(ChangeIdWrapper { inner: Some(ChangeId::Id(id)) }) =
+                    toml::from_str::<toml::Value>(&contents)
+                        .and_then(|table: toml::Value| ChangeIdWrapper::deserialize(table))
                 {
+                    let changes = crate::find_recent_config_change_ids(id);
                     if !changes.is_empty() {
                         println!(
                             "WARNING: There have been changes to x.py since you last updated:\n{}",

src/bootstrap/src/core/config/tests.rs

@@ -10,6 +10,7 @@ use serde::Deserialize;
 
 use super::flags::Flags;
 use super::{ChangeIdWrapper, Config, RUSTC_IF_UNCHANGED_ALLOWED_PATHS};
+use crate::ChangeId;
 use crate::core::build_steps::clippy::{LintConfig, get_clippy_rules_in_order};
 use crate::core::build_steps::llvm;
 use crate::core::build_steps::llvm::LLVM_INVALIDATION_PATHS;
@@ -171,7 +172,7 @@ runner = "x86_64-runner"
             )
         },
     );
-    assert_eq!(config.change_id, Some(1), "setting top-level value");
+    assert_eq!(config.change_id, Some(ChangeId::Id(1)), "setting top-level value");
     assert_eq!(
         config.rust_lto,
         crate::core::config::RustcLto::Fat,
@@ -311,7 +312,7 @@ fn parse_change_id_with_unknown_field() {
     "#;
 
     let change_id_wrapper: ChangeIdWrapper = toml::from_str(config).unwrap();
-    assert_eq!(change_id_wrapper.inner, Some(3461));
+    assert_eq!(change_id_wrapper.inner, Some(ChangeId::Id(3461)));
 }
 
 #[test]

src/bootstrap/src/lib.rs

@@ -45,8 +45,8 @@ mod core;
 mod utils;
 
 pub use core::builder::PathSet;
-pub use core::config::Config;
 pub use core::config::flags::{Flags, Subcommand};
+pub use core::config::{ChangeId, Config};
 
 #[cfg(feature = "tracing")]
 use tracing::{instrument, span};