dap: utilize the container filesystem for the file explorer

dap/thread.go

@@ -16,6 +16,7 @@ import (
 	"github.com/moby/buildkit/solver/pb"
 	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
+	"github.com/tonistiigi/fsutil/types"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -323,16 +324,12 @@ func (t *thread) pause(c Context, k string, refs map[string]gateway.Reference, e
 	}
 	t.paused = make(chan stepType, 1)
 
+	t.prepareResultHandle(c, k, refs, err)
+
 	ctx, cancel := context.WithCancelCause(c)
 	t.collectStackTrace(ctx, pos, refs)
 	t.cancel = cancel
 
-	// Used for exec. Only works if there was an error or if the step returns
-	// a root mount.
-	if ref, ok := refs[k]; ok || err != nil {
-		t.prepareResultHandle(c, ref, err)
-	}
-
 	event.ThreadId = t.id
 	c.C() <- &dap.StoppedEvent{
 		Event: dap.Event{Event: "stopped"},
@@ -341,7 +338,15 @@ func (t *thread) pause(c Context, k string, refs map[string]gateway.Reference, e
 	return t.paused
 }
 
-func (t *thread) prepareResultHandle(c Context, ref gateway.Reference, err error) {
+func (t *thread) prepareResultHandle(c Context, k string, refs map[string]gateway.Reference, err error) {
+	var ref gateway.Reference
+	if err == nil {
+		var ok bool
+		if ref, ok = refs[k]; !ok {
+			return
+		}
+	}
+
 	// Create a context for cancellations and make the cancel function
 	// block on the wait group.
 	var wg sync.WaitGroup
@@ -353,6 +358,26 @@ func (t *thread) prepareResultHandle(c Context, ref gateway.Reference, err error
 
 	t.rCtx = build.NewResultHandle(ctx, t.c, ref, t.meta, err)
 
+	if err != nil {
+		var solveErr *errdefs.SolveError
+		if errors.As(err, &solveErr) {
+			if exec, ok := solveErr.Op.Op.(*pb.Op_Exec); ok {
+				rCtx := t.rCtx
+
+				getContainer := sync.OnceValues(func() (gateway.Container, error) {
+					return rCtx.NewContainer(ctx, &build.InvokeConfig{})
+				})
+
+				for i, m := range exec.Exec.Mounts {
+					refs[m.Dest] = &mountReference{
+						getContainer: getContainer,
+						index:        i,
+					}
+				}
+			}
+		}
+	}
+
 	// Start the attach. Use the context we created and perform it in
 	// a goroutine. We aren't necessarily assuming this will actually work.
 	wg.Add(1)
@@ -680,3 +705,52 @@ func (t *thread) rewind(ctx Context, inErr error) (k string, result *step, mount
 	}
 	return k, result, mounts, inErr
 }
+
+type mountReference struct {
+	getContainer func() (gateway.Container, error)
+	index        int
+}
+
+func (r *mountReference) ToState() (llb.State, error) {
+	return llb.State{}, errors.New("unimplemented")
+}
+
+func (r *mountReference) Evaluate(ctx context.Context) error {
+	return nil
+}
+
+func (r *mountReference) ReadFile(ctx context.Context, req gateway.ReadRequest) ([]byte, error) {
+	ctr, err := r.getContainer()
+	if err != nil {
+		return nil, err
+	}
+
+	return ctr.ReadFile(ctx, gateway.ReadContainerRequest{
+		ReadRequest: req,
+		Index:       r.index,
+	})
+}
+
+func (r *mountReference) StatFile(ctx context.Context, req gateway.StatRequest) (*types.Stat, error) {
+	ctr, err := r.getContainer()
+	if err != nil {
+		return nil, err
+	}
+
+	return ctr.StatFile(ctx, gateway.StatContainerRequest{
+		StatRequest: req,
+		Index:       r.index,
+	})
+}
+
+func (r *mountReference) ReadDir(ctx context.Context, req gateway.ReadDirRequest) ([]*types.Stat, error) {
+	ctr, err := r.getContainer()
+	if err != nil {
+		return nil, err
+	}
+
+	return ctr.ReadDir(ctx, gateway.ReadDirContainerRequest{
+		ReadDirRequest: req,
+		Index:          r.index,
+	})
+}

go.mod

@@ -180,3 +180,5 @@ require (
 
 // restore junctions to have os.ModeSymlink flag set on Windows: https://github.com/docker/buildx/issues/3221
 godebug winsymlink=0
+
+replace github.com/moby/buildkit => github.com/jsternberg/buildkit v0.12.1-0.20260108212518-d47b53f94598

go.sum

@@ -189,6 +189,8 @@ github.com/josharian/intern v1.0.0 h1:vlS4z54oSdjm0bgjRigI+G1HpF+tI+9rE5LLzOg8Hm
 github.com/josharian/intern v1.0.0/go.mod h1:5DoeVV0s6jJacbCEi61lwdGj/aVlrQvzHFFd8Hwg//Y=
 github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnrnM=
 github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
+github.com/jsternberg/buildkit v0.12.1-0.20260108212518-d47b53f94598 h1:cWId6kOBQvY6PHRhlRTnFx/TTrZaKjol6rlh1ogfPsY=
+github.com/jsternberg/buildkit v0.12.1-0.20260108212518-d47b53f94598/go.mod h1:LtUhyzVLAD0ilniDZRbghEyRq9CgZAY7ywMXlVo9MBI=
 github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/klauspost/compress v1.18.2 h1:iiPHWW0YrcFgpBYhsA6D1+fqHssJscY/Tm/y2Uqnapk=
@@ -210,8 +212,6 @@ github.com/mitchellh/go-wordwrap v1.0.1 h1:TLuKupo69TCn6TQSyGxwI1EblZZEsQ0vMlAFQ
 github.com/mitchellh/go-wordwrap v1.0.1/go.mod h1:R62XHJLzvMFRBbcrT7m7WgmE1eOyTSsCt+hzestvNj0=
 github.com/mitchellh/hashstructure/v2 v2.0.2 h1:vGKWl0YJqUNxE8d+h8f6NJLcCJrgbhC4NcD46KavDd4=
 github.com/mitchellh/hashstructure/v2 v2.0.2/go.mod h1:MG3aRVU/N29oo/V/IhBX8GR/zz4kQkprJgF2EVszyDE=
-github.com/moby/buildkit v0.26.1-0.20260106154623-ed6dc749ce40 h1:h45o8dTo7Cq1Su49bs9VHP83Fdp3olgMfgo3tZULXUw=
-github.com/moby/buildkit v0.26.1-0.20260106154623-ed6dc749ce40/go.mod h1:LtUhyzVLAD0ilniDZRbghEyRq9CgZAY7ywMXlVo9MBI=
 github.com/moby/docker-image-spec v1.3.1 h1:jMKff3w6PgbfSa69GfNg+zN/XLhfXJGnEx3Nl2EsFP0=
 github.com/moby/docker-image-spec v1.3.1/go.mod h1:eKmb5VW8vQEh/BAr2yvVNvuiJuY6UIocYsFu/DxxRpo=
 github.com/moby/go-archive v0.2.0 h1:zg5QDUM2mi0JIM9fdQZWC7U8+2ZfixfTYoHL7rWUcP8=