From b2bc801cd061304cbeaec6b368ea89b96f439d69 Mon Sep 17 00:00:00 2001
From: Andrea Luzzardi <aluzzardi@gmail.com>
Date: Wed, 24 Feb 2021 15:38:03 -0800
Subject: [PATCH] fix caching issues with Local

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>
---
 dagger/pipeline.go | 33 ++++++++++++++++++++++++++-------
 dagger/solver.go   |  4 ++++
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/dagger/pipeline.go b/dagger/pipeline.go
index 84d31681..2a2e17f8 100644
--- a/dagger/pipeline.go
+++ b/dagger/pipeline.go
@@ -253,14 +253,33 @@ func (p *Pipeline) Local(ctx context.Context, op *compiler.Value) error {
 			return err
 		}
 	}
+	// FIXME: Remove the `Copy` and use `Local` directly.
+	//
+	// Copy'ing is a costly operation which should be unnecessary.
+	// However, for a mysterious reason, `llb.Local` is returning a different
+	// digest at every run, therefore invalidating the cache.
+	//
+	// By wrapping `llb.Local` inside `llb.Copy`, we get the same digest for
+	// the same content.
+	p.fs = p.fs.Change(func(st llb.State) llb.State {
+		return st.File(
+			llb.Copy(
+				llb.Local(
+					dir,
+					llb.FollowPaths(include),
+					llb.WithCustomName(p.vertexNamef("Local %s", dir)),
+
+					// Without hint, multiple `llb.Local` operations on the
+					// same path get a different digest.
+					llb.SessionID(p.s.SessionID()),
+					llb.SharedKeyHint(dir),
+				),
+				"/",
+				"/",
+			),
+		)
+	})
 
-	p.fs = p.fs.Set(
-		llb.Local(
-			dir,
-			llb.FollowPaths(include),
-			llb.WithCustomName(p.vertexNamef("Local %s", dir)),
-		),
-	)
 	return nil
 }
 
diff --git a/dagger/solver.go b/dagger/solver.go
index eddac981..c4e6ebf0 100644
--- a/dagger/solver.go
+++ b/dagger/solver.go
@@ -35,6 +35,10 @@ func (s Solver) Scratch() FS {
 	return s.FS(llb.Scratch())
 }
 
+func (s Solver) SessionID() string {
+	return s.c.BuildOpts().SessionID
+}
+
 // Solve will block until the state is solved and returns a Reference.
 func (s Solver) SolveRequest(ctx context.Context, req bkgw.SolveRequest) (bkgw.Reference, error) {
 	// call solve