From 33af2cb98795e9fd2af1a301a839288b571d1efb Mon Sep 17 00:00:00 2001
From: Andy Arthur <andy@dolthub.com>
Date: Sun, 21 Feb 2021 13:27:35 -0800
Subject: [PATCH] save active merge commit during GC

---
 go/cmd/dolt/commands/gc.go                    | 18 ++++++++++---
 go/libraries/doltcore/env/repo_state.go       | 14 +++++++++++
 .../doltcore/mvdata/table_data_loc.go         | 25 ++++++++++++++-----
 3 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/go/cmd/dolt/commands/gc.go b/go/cmd/dolt/commands/gc.go
index 97fbf58b77..e0050352cf 100644
--- a/go/cmd/dolt/commands/gc.go
+++ b/go/cmd/dolt/commands/gc.go
@@ -17,6 +17,8 @@ package commands
 import (
 	"context"
 
+	"github.com/dolthub/dolt/go/store/hash"
+
 	"github.com/dolthub/dolt/go/cmd/dolt/cli"
 	"github.com/dolthub/dolt/go/cmd/dolt/errhand"
 	eventsapi "github.com/dolthub/dolt/go/gen/proto/dolt/services/eventsapi/v1alpha1"
@@ -114,11 +116,21 @@ func (cmd GarbageCollectionCmd) Exec(ctx context.Context, commandStr string, arg
 			return HandleVErrAndExitCode(verr, usage)
 		}
 
-		w := dEnv.RepoState.WorkingHash()
-		s := dEnv.RepoState.StagedHash()
+		keepers := []hash.Hash{
+			dEnv.RepoState.WorkingHash(),
+			dEnv.RepoState.StagedHash(),
+		}
 
-		err = dEnv.DoltDB.GC(ctx, w, s)
+		if dEnv.IsMergeActive() {
+			m, err := env.ResolveMergeCommitHash(ctx, dEnv.RepoStateReader(), dEnv.DoltDB)
+			if err != nil {
+				verr = errhand.BuildDError("an error occurred while saving an active merge commit").AddCause(err).Build()
+				return HandleVErrAndExitCode(verr, usage)
+			}
+			keepers = append(keepers, m)
+		}
 
+		err = dEnv.DoltDB.GC(ctx, keepers...)
 		if err != nil {
 			verr = errhand.BuildDError("an error occurred during garbage collection").AddCause(err).Build()
 		}
diff --git a/go/libraries/doltcore/env/repo_state.go b/go/libraries/doltcore/env/repo_state.go
index daa29955b5..33e92349c3 100644
--- a/go/libraries/doltcore/env/repo_state.go
+++ b/go/libraries/doltcore/env/repo_state.go
@@ -340,6 +340,20 @@ func MergeWouldStompChanges(ctx context.Context, mergeCommit *doltdb.Commit, dbD
 	return stompedTables, headWorkingDiffs, nil
 }
 
+func ResolveMergeCommitHash(ctx context.Context, rsr RepoStateReader, ddb *doltdb.DoltDB) (h hash.Hash, err error) {
+	spec, err := doltdb.NewCommitSpec(rsr.GetMergeCommit())
+	if err != nil {
+		return h, err
+	}
+
+	cm, err := ddb.Resolve(ctx, spec, nil)
+	if err != nil {
+		return h, err
+	}
+
+	return cm.HashOf()
+}
+
 func mapTableHashes(ctx context.Context, root *doltdb.RootValue) (map[string]hash.Hash, error) {
 	names, err := root.GetTableNames(ctx)
 
diff --git a/go/libraries/doltcore/mvdata/table_data_loc.go b/go/libraries/doltcore/mvdata/table_data_loc.go
index 379d5e9dad..98c03e799b 100644
--- a/go/libraries/doltcore/mvdata/table_data_loc.go
+++ b/go/libraries/doltcore/mvdata/table_data_loc.go
@@ -19,6 +19,8 @@ import (
 	"errors"
 	"sync/atomic"
 
+	"github.com/dolthub/dolt/go/store/hash"
+
 	"github.com/dolthub/dolt/go/libraries/doltcore/doltdb"
 	"github.com/dolthub/dolt/go/libraries/doltcore/env"
 	"github.com/dolthub/dolt/go/libraries/doltcore/row"
@@ -278,20 +280,31 @@ func (te *tableEditorWriteCloser) GC(ctx context.Context) error {
 		return nil
 	}
 
-	w := te.dEnv.RepoState.WorkingHash()
-	s := te.dEnv.RepoState.StagedHash()
-
-	inProgresRoot, err := te.sess.Flush(ctx)
+	inProgressRoot, err := te.sess.Flush(ctx)
 	if err != nil {
 		return err
 	}
 
-	i, err := te.dEnv.DoltDB.WriteRootValue(ctx, inProgresRoot)
+	inProgressHash, err := te.dEnv.DoltDB.WriteRootValue(ctx, inProgressRoot)
 	if err != nil {
 		return err
 	}
 
-	return te.dEnv.DoltDB.GC(ctx, w, s, i)
+	keepers := []hash.Hash{
+		te.dEnv.RepoState.WorkingHash(),
+		te.dEnv.RepoState.StagedHash(),
+		inProgressHash,
+	}
+
+	if te.dEnv.IsMergeActive() {
+		m, err := env.ResolveMergeCommitHash(ctx, te.dEnv.RepoStateReader(), te.dEnv.DoltDB)
+		if err != nil {
+			return err
+		}
+		keepers = append(keepers, m)
+	}
+
+	return te.dEnv.DoltDB.GC(ctx, keepers...)
 }
 
 // Close implements TableWriteCloser