From cddacacb46dba3dab26dfaae65f82d4ac0737cde Mon Sep 17 00:00:00 2001
From: Mac Malone <tydeu@hatpress.net>
Date: Wed, 11 Feb 2026 18:33:09 -0500
Subject: [PATCH] feat: lake: `lake cache clean` (#12444)

This PR adds the Lake CLI command `lake cache clean`, which deletes the
Lake cache directory.
---
 src/lake/Lake/CLI/Help.lean       | 14 +++++++++++++-
 src/lake/Lake/CLI/Main.lean       | 15 +++++++++++++++
 src/lake/Lake/Load/Workspace.lean |  3 ++-
 tests/lake/tests/cache/test.sh    |  7 ++++++-
 4 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/lake/Lake/CLI/Help.lean b/src/lake/Lake/CLI/Help.lean
index ac8cc264f9..f43578d337 100644
--- a/src/lake/Lake/CLI/Help.lean
+++ b/src/lake/Lake/CLI/Help.lean
@@ -355,8 +355,9 @@ USAGE:
   lake cache <COMMAND>
 
 COMMANDS:
-  get [<mappings>]      download artifacts into the Lake cache
+  get [<mappings>]      download artifacts into the local Lake cache
   put <mappings>        upload artifacts to a remote cache
+  clean                 removes ALL froms the local Lake cache
 
 See `lake cache help <command>` for more information on a specific command."
 
@@ -448,6 +449,16 @@ derived from the package's current Git revision (and prefixed by the
 full scope). As such, the command will warn if the work tree currently
 has changes."
 
+def helpCacheClean :=
+"Removes ALL files from the local Lake cache
+
+USAGE:
+  lake cache clean
+
+Deletes the configured Lake cache directory. If a workspace configuration
+exists, this will delete the cache directory it uses. Otherwise, it will
+delete the default Lake cache directory for the system."
+
 def helpScriptCli :=
 "Manage Lake scripts
 
@@ -578,6 +589,7 @@ public def helpScript : (cmd : String) → String
 public def helpCache : (cmd : String) → String
 | "get"                 => helpCacheGet
 | "put"                 => helpCachePut
+| "clean"               => helpCacheClean
 | _                     => helpCacheCli
 
 public def help : (cmd : String) → String
diff --git a/src/lake/Lake/CLI/Main.lean b/src/lake/Lake/CLI/Main.lean
index 6b7b5c00b1..db10c07b8e 100644
--- a/src/lake/Lake/CLI/Main.lean
+++ b/src/lake/Lake/CLI/Main.lean
@@ -537,6 +537,20 @@ protected def add : CliM PUnit := do
   let map ← CacheMap.load file
   ws.lakeCache.writeMap scope map opts.service?
 
+protected def clean : CliM PUnit := do
+  processOptions lakeOption
+  let opts ← getThe LakeOptions
+  noArgsRem do
+  let cfg ← mkLoadConfig opts
+  let dir ← id do
+    if (← configFileExists cfg.configFile) then
+      return (← loadWorkspaceRoot cfg).lakeCache.dir
+    else if let some cache := cfg.lakeEnv.lakeCache? then
+      return cache.dir
+    else
+      error "no cache to delete; no workspace configuration found and no system cache detected"
+  IO.FS.removeDirAll dir
+
 protected def help : CliM PUnit := do
   IO.println <| helpCache <| ← takeArgD ""
 
@@ -546,6 +560,7 @@ def cacheCli : (cmd : String) → CliM PUnit
 | "add"   => cache.add
 | "get"   => cache.get
 | "put"   => cache.put
+| "clean" => cache.clean
 | "help"  => cache.help
 | cmd     => throw <| CliError.unknownCommand cmd
 
diff --git a/src/lake/Lake/Load/Workspace.lean b/src/lake/Lake/Load/Workspace.lean
index 8b8cc73843..3ee261edb1 100644
--- a/src/lake/Lake/Load/Workspace.lean
+++ b/src/lake/Lake/Load/Workspace.lean
@@ -23,10 +23,11 @@ open Lean
 namespace Lake
 
 /--
+**For internal use only.**
 Load a `Workspace` for a Lake package by elaborating its configuration file.
 Does not resolve dependencies.
 -/
-private def loadWorkspaceRoot (config : LoadConfig) : LogIO Workspace := do
+public def loadWorkspaceRoot (config : LoadConfig) : LogIO Workspace := do
   Lean.searchPathRef.set config.lakeEnv.leanSearchPath
   let (root, env?) ← loadPackageCore "[root]" {config with pkgIdx := 0}
   let root := {root with outputsRef? := ← CacheRef.mk}
diff --git a/tests/lake/tests/cache/test.sh b/tests/lake/tests/cache/test.sh
index ba010accb9..e7da511892 100755
--- a/tests/lake/tests/cache/test.sh
+++ b/tests/lake/tests/cache/test.sh
@@ -180,8 +180,13 @@ test_lines 3 .lake/outputs.jsonl
 test_run build Test:static -o .lake/outputs.jsonl
 test_lines 6 .lake/outputs.jsonl
 
-# Verify all artifacts end up in the cache directory with `restoreAllArtifacts`
+# Verify that `lake cache clean` deletes the cache directory
+test_exp -d "$CACHE_DIR"
 test_cmd cp -r "$CACHE_DIR" .lake/cache-backup
+test_run cache clean
+test_exp ! -d "$CACHE_DIR"
+
+# Verify all artifacts end up in the cache directory with `restoreAllArtifacts`
 test_cmd rm -rf "$CACHE_DIR" .lake/build
 test_run build -R -KrestoreAll=true \
   test:exe Test:static Test:shared +Test:o.export +Test:o.noexport +Module