feat(toolchain): support default toolchain aliases by 14elias · Pull Request #5071 · rust-lang/rustup

14elias · 2026-09-12T05:32:28Z

Related to #5025.

this change Allows default to be used as a toolchain alias and resolve it to the configured default toolchain.
This makes default usable consistently across the supported override mechanisms, including +default, RUSTUP_TOOLCHAIN=default, directory overrides, and rust-toolchain files.
For example, when the configured default toolchain is stable: +default, RUSTUP_TOOLCHAIN=default all resolve to the configured stable toolchain.
A toolchain file containing:
[toolchain]
channel = "default"
also resolves to the configured default toolchain.

Tests

+default resolution.
RUSTUP_TOOLCHAIN=default.
rust-toolchain.toml using channel = "default".

rami3l · 2026-09-14T06:52:29Z

                    Some(ResolvableToolchainName::Official(t)) => Some(t),
                    // Default is custom, presumably from a prior install. Do nothing.
                    Some(ResolvableToolchainName::Custom(_)) => None,
+                    // The configured default cannot itself be the default alias.


I think this change is redundant now.

View changes since the review

rami3l · 2026-09-14T06:56:31Z

+}
+
+impl Display for ToolchainAlias {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {


Suggest importing std::fmt.

View changes since the review

the existing code uses this pattern that's why i used that but i can import std::fmt and change in all the places if you want.

rami3l · 2026-09-14T06:57:17Z

+        if value == "default" {
+            Ok(Self::Default)
+        } else {
+            Err(InvalidName::ToolchainName(value.into()))
+        }


Suggest using match instead of if here so that we can easily add more variants (with exhaustiveness check).

View changes since the review

rami3l · 2026-09-14T06:57:58Z

+/// An alias for a toolchain name.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub enum ToolchainAlias {
+    Default,


Suggest adding a docstring explaining the precise semantics of each variant.

View changes since the review

///Refers to rustup's configured default toolchain.
///Parsed from the literal string "default". is this docstring good at representing the variant

@14elias I think just keeping the first line would be fine. Also could you write your comments, PR descriptions etc in proper formatted markdown? It's not super easy to read to me in its current state.

rami3l · 2026-09-14T07:01:11Z

+    type Err = InvalidName;
+
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        if let Ok(candidate) = validate_name(value)


This check makes no sense because it overlaps with the latter check. Note that your aliases are a predetermined set of strings.

View changes since the review

i kept validate_name() in ToolchainOverride::from_str() because it allow input +default/ as +stable/ . but if aliases should only accept exact names then checking if the value is alias is enough.

rami3l · 2026-09-14T07:12:10Z

+impl ToolchainOverride<ResolvableToolchainName> {
+    pub fn resolve(self, cfg: &Cfg<'_>) -> anyhow::Result<ResolvableToolchainName> {
+        match self {
+            Self::Alias(ToolchainAlias::Default) => cfg
+                .get_default_resolvable()?
+                .ok_or_else(|| no_toolchain_error(cfg.process)),
+            Self::Explicit(r) => Ok(r),
+        }
+    }
+}
+
+impl ToolchainOverride<ResolvableLocalToolchainName> {
+    pub fn resolve(self, cfg: &Cfg<'_>) -> anyhow::Result<ResolvableLocalToolchainName> {
+        match self {
+            Self::Alias(ToolchainAlias::Default) => {
+                let default = cfg
+                    .get_default_resolvable()?
+                    .ok_or_else(|| no_toolchain_error(cfg.process))?;
+                Ok(ResolvableLocalToolchainName::Named(default))
+            }
+            Self::Explicit(r) => Ok(r),
+        }
+    }
+}
+
+impl ToolchainOverride<MaybeResolvableToolchainName> {
+    pub fn resolve(self, cfg: &Cfg<'_>) -> anyhow::Result<MaybeResolvableToolchainName> {
+        match self {
+            Self::Alias(ToolchainAlias::Default) => {
+                let default = cfg
+                    .get_default_resolvable()?
+                    .ok_or_else(|| anyhow::anyhow!("no default toolchain is configured"))?;
+                Ok(MaybeResolvableToolchainName::Some(default))
+            }
+            Self::Explicit(r) => Ok(r),
+        }
+    }
+}


It should be able to replace all this with a single, generic impl block with an appropriate use of the From trait. Suggest adding the necessary From implementations if needed.

View changes since the review

rami3l · 2026-09-14T07:15:45Z

+
+/// A wrapper for types that can be overridden by an alias.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub enum ToolchainOverride<T> {


Since the uses of this type are always of the form ToolchainOverride<xxxToolchain>, suggest renaming this to just Override.

View changes since the review

rami3l · 2026-09-14T07:17:37Z

+/// A wrapper for types that can be overridden by an alias.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub enum ToolchainOverride<T> {
+    Alias(ToolchainAlias),


Suggest using the same part of speech (preferably adjective) for all variants. In this case I'd suggest Aliased to mirror Explicit.

View changes since the review

rami3l · 2026-09-14T07:18:10Z

-        match toolchain.to_owned() {
+        let toolchain = toolchain.resolve(cfg)?;
+
+        match toolchain {


Suggest inlining this temporary variable toolchain.

View changes since the review

rami3l · 2026-09-14T07:19:49Z

-                ActiveSource::CommandLine,
-            )),
+            Some(name) => {
+                let name = name.resolve(&cfg)?;


Suggest inlining this temporary variable name.

View changes since the review

rami3l · 2026-09-14T07:40:30Z

@@ -5,7 +5,7 @@
    command::run_command_for_dir,


The category specified in the commit message is wrong. It should look more like feat(toolchain): or similar. Same thing for the title of this PR.

View changes since the review

rami3l · 2026-09-14T10:18:30Z

@@ -1,2 +1,2 @@
 use std::{path::PathBuf, process::ExitStatus, str::FromStr};



Besides, if you have used LLM/agents to draft this PR, please properly disclose the fact in the PR description according to our contribution guidelines. Otherwise, I may close this PR without any prior warnings.

View changes since the review

sorry for the confusion or inconvenience caused, but i did not used AI agent or LLM to write the code, or draft this PR description. i used LLM to brainstorm how to solve the problem specifically after you suggested me to create new data type instead of mixing the alias Default variant to the real tool chain variants and also i used github copilot to check if i applied ToolchainOverride consistently across the relevant functions and return types and i tested everything by myself, but i will add the tools i used for help when i update the PR description. thanks for checking.

i also used github copilot to help me with tests i mean the role is not like writing the tests it is just like discussing the edge cases and checking what i write and telling me to update the parts i have to modify and what i have to cover. that is how i use AI

rustbot · 2026-09-14T20:06:54Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

rami3l requested changes Sep 12, 2026

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Comment thread src/cli/rustup_mode.rs Outdated

Comment thread src/cli/rustup_mode.rs Outdated

14elias force-pushed the feat/add_default branch from 7b83b06 to d168934 Compare September 13, 2026 03:23

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14elias force-pushed the feat/add_default branch from d168934 to 8982db1 Compare September 13, 2026 03:34

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14elias force-pushed the feat/add_default branch from 8982db1 to de81ab2 Compare September 13, 2026 04:15

rami3l requested changes Sep 14, 2026

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rami3l reviewed Sep 14, 2026

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14elias changed the title ~~test: support default toolchain aliases~~ feat(toolchain): support default toolchain aliases Sep 14, 2026

feat(toolchain):support default toolchain aliases

802fa8e

14elias force-pushed the feat/add_default branch from de81ab2 to 802fa8e Compare September 14, 2026 20:06

		@@ -1,2 +1,2 @@
		use std::{path::PathBuf, process::ExitStatus, str::FromStr};

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