fix: canonicalize toolchains_dir when checking if inside a toolchain

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+- Fix detection of being inside a toolchain directory on Windows when the path is reported with a lowercase drive letter (#199).
+
 # 4.2.1 - 2026-03-18
 
 - Fix combining `elan override` with new path-based toolchains.

CLAUDE.md

@@ -0,0 +1,145 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**elan** is a toolchain version manager for the Lean theorem prover, forked from rustup. It manages multiple Lean installations and automatically selects the correct version based on `lean-toolchain` files in projects. The binary is a chimera that changes behavior based on its invocation name:
+- `elan`/`elan-init`: Main CLI application and installer
+- `lean`, `lake`, etc.: Proxies that delegate to the correct toolchain version
+
+## Build Commands
+
+### Basic Build
+```bash
+cargo build
+# Output: target/debug/elan-init
+```
+
+### Release Build
+```bash
+cargo build --release
+# Output: target/release/elan-init
+```
+
+### Cross-compilation (used in CI)
+```bash
+cargo install cross --locked
+cross build --release --target <TARGET>
+# Examples: x86_64-unknown-linux-musl, aarch64-apple-darwin, x86_64-pc-windows-msvc
+```
+
+### Testing
+```bash
+cargo test --release --target <TARGET>
+```
+
+### Windows Build Requirements
+- 64-bit developer command prompt
+- Windows version of perl.exe from https://strawberryperl.com/ (must be first in PATH, not Git's perl)
+
+## Architecture
+
+### Binary Dispatch (src/elan-cli/main.rs)
+The main entry point determines behavior by examining arg0:
+- `elan` → `elan_mode::main()` - CLI commands
+- `elan-init` / `elan-setup*` → `setup_mode::main()` - Installation
+- `elan-gc-*` → `self_update::complete_windows_uninstall()` - Windows cleanup
+- Any other name → `proxy_mode::main()` - Tool proxying (lean, lake, etc.)
+
+Recursion guard via `LEAN_RECURSION_COUNT` environment variable prevents infinite proxy loops.
+
+### Workspace Structure
+This is a Cargo workspace with four crates:
+- `elan` (src/elan/lib.rs): Core library with config, toolchain resolution, and installation logic
+- `elan-init` (src/elan-cli/): Main binary and CLI implementation
+- `elan-dist` (src/elan-dist/): Distribution management, manifests, and component installation
+- `elan-utils` (src/elan-utils/): Shared utilities
+- `download` (src/download/): HTTP download functionality (curl-backend or reqwest-backend)
+
+### Key Concepts
+
+**Toolchain Resolution** (src/elan/toolchain.rs, src/elan/config.rs):
+- Toolchain descriptors can be:
+  - `Remote`: Downloaded from GitHub releases (e.g., `leanprover/lean4:v4.0.0`)
+  - `Local`: Custom linked toolchains
+- Resolution hierarchy checks (in order):
+  1. `ELAN_TOOLCHAIN` environment variable
+  2. Directory override (`elan override set`)
+  3. `lean-toolchain` file in current/parent directories
+  4. `leanpkg.toml` file (legacy)
+  5. Inside a toolchain directory itself
+  6. Default toolchain from settings
+
+**Proxy Mode** (src/elan-cli/proxy_mode.rs):
+When elan is called as `lean`, `lake`, etc., it:
+1. Checks for `+toolchain` as first argument for explicit toolchain selection
+2. Resolves which toolchain to use for current directory
+3. Executes the real binary from that toolchain's directory
+
+**Configuration** (src/elan/config.rs):
+- ELAN_HOME: `~/.elan` (configurable)
+- Settings file: `~/.elan/settings.toml` (default toolchain, overrides)
+- Toolchains directory: `~/.elan/toolchains/`
+- Temporary directory: `~/.elan/tmp/`
+
+### CLI Commands (src/elan-cli/elan_mode.rs)
+Main commands implemented:
+- `show`: Display active and installed toolchains
+- `install/uninstall`: Manage toolchains
+- `default`: Set default toolchain
+- `override set/unset/list`: Per-directory toolchain overrides
+- `toolchain link`: Create custom toolchain from local directory
+- `toolchain gc`: Garbage-collect unused toolchains
+- `run`: Run command with specific toolchain
+- `which`: Show path to binary
+- `doc/man`: Open documentation
+- `self update/uninstall`: Manage elan itself
+- `completions`: Generate shell completions
+
+### Download Backend
+Two features control HTTP backend (default: curl-backend):
+- `curl-backend`: Uses libcurl
+- `reqwest-backend`: Pure Rust alternative
+
+### Feature Flags
+- `no-self-update`: Disable self-update functionality (for package managers)
+- `msi-installed`: Changes self-update/uninstall behavior for Windows MSI installations
+
+## Installation Flow
+1. `elan-init.sh` or `elan-init.ps1` downloads and runs `elan-init` binary
+2. Setup mode installs to `~/.elan`, adds to PATH via shell config
+3. Creates symlinks: `elan`, `lean`, `lake` → `elan-init`
+4. Downloads default toolchain on first use
+
+## Commit Messages
+
+Write the subject as `<type>: <summary> (#<PR or issue>)` (e.g. `fix: path-based toolchain as override (#195)`). A body is optional; when present, separate it from the subject with a blank line and write each paragraph as one long line — do not hard-wrap inside a paragraph. Blank lines between paragraphs are fine.
+
+## Changelog
+
+User-facing fixes and features must add a bullet to `CHANGELOG.md` in the same commit. Add to (or create) the top `# Unreleased` section — at release time it becomes `# X.Y.Z - YYYY-MM-DD`. Pure internal refactors, test-only changes, and `chore:` commits don't need an entry.
+
+## Testing Strategy
+No unit tests (marked `test = false` in Cargo.toml). Integration testing via:
+- CI runs build, test, and install test on all platforms
+- Install test: runs `elan-init -y`, creates new lake project, builds it
+
+## Development Notes
+
+### Rustup Legacy
+This codebase is a fork of rustup with terminology changes:
+- rustup → elan
+- cargo → lake
+- rust(c) → lean
+- CARGO_HOME merged with RUSTUP_HOME
+
+### Toolchain Naming
+Toolchains follow pattern: `[origin/][owner/repo:]release`
+- Default origin: `leanprover/lean4` (becomes `leanprover/lean4-nightly` for nightly builds)
+- Nightly releases: `nightly-YYYY-MM-DD`
+- Stable releases: `vX.Y.Z` or `X.Y.Z` (auto-prefixed with `v`)
+- Special channels: `stable`, `beta`, `nightly`, `lean-toolchain` (resolve to latest local)
+
+### NixOS Support
+Toolchains require patching on NixOS - handled by Nixpkgs version. See `fetch_nixos_patch.sh`.

src/elan/config.rs

@@ -224,7 +224,9 @@ impl Cfg {
 
             dir = d.parent();
 
-            if dir == Some(&self.toolchains_dir) {
+            // NOTE: `dir` is already canonicalized, so `==` should be good here
+            let toolchains_dir = utils::canonicalize_path(&self.toolchains_dir, &|n| notify(n.into()));
+            if dir == Some(&*toolchains_dir) {
                 if let Some(last) = d.file_name() {
                     if let Some(last) = last.to_str() {
                         return Ok(Some((
@@ -368,3 +370,48 @@ impl Cfg {
         toolchain.open_docs(relative)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs;
+    use tempfile::TempDir;
+
+    fn make_cfg(elan_dir: PathBuf, toolchains_dir: PathBuf) -> Cfg {
+        Cfg {
+            settings_file: SettingsFile::new(elan_dir.join("settings.toml")),
+            temp_cfg: temp::Cfg::new(elan_dir.join("tmp"), Box::new(|_| {})),
+            elan_dir,
+            toolchains_dir,
+            env_override: None,
+            notify_handler: Arc::new(|_| {}),
+        }
+    }
+
+    // Regression test for #161: on Windows, `cwd` can come back with a
+    // lowercase `c:` while `self.toolchains_dir` (built from env vars) has
+    // `C:`, so the raw equality check failed and elan didn't recognize the
+    // user was inside a toolchain. We simulate the same canonical-vs-raw
+    // mismatch on Linux by giving `toolchains_dir` extra `..` components.
+    #[test]
+    fn detects_inside_toolchain_dir_when_toolchains_dir_path_is_not_canonical() {
+        let elan = TempDir::new().unwrap();
+        let tc_dir = elan
+            .path()
+            .join("toolchains")
+            .join("leanprover--lean4---v4.0.0");
+        fs::create_dir_all(&tc_dir).unwrap();
+
+        let toolchains_dir = elan.path().join("toolchains").join("..").join("toolchains");
+        let cfg = make_cfg(elan.path().to_path_buf(), toolchains_dir);
+
+        let result = cfg
+            .find_override_from_dir_walk(&tc_dir, &Settings::default())
+            .unwrap();
+
+        match result {
+            Some((_, OverrideReason::InToolchainDirectory(_))) => {}
+            other => panic!("expected InToolchainDirectory, got {other:?}"),
+        }
+    }
+}