No-op merge message in CLI

go/cmd/dolt/commands/merge.go

@@ -144,24 +144,34 @@ func (cmd MergeCmd) Exec(ctx context.Context, commandStr string, args []string,
 		cli.Println(err.Error())
 		return 1
 	}
-	// if merge is called with '--no-commit', we need to commit the sql transaction or the staged changes will be lost
-	_, _, err = queryist.Query(sqlCtx, "COMMIT")
+	rows, err := sql.RowIterToRows(sqlCtx, rowIter)
 	if err != nil {
 		cli.Println(err.Error())
+		return 0
+	}
+	if len(rows) != 1 {
+		cli.Println("Runtime error: merge operation returned unexpected number of rows: ", len(rows))
 		return 1
 	}
-	rows, err := sql.RowIterToRows(sqlCtx, rowIter)
+	mergeResultRow := rows[0]
+
+	upToDate, err := everythingUpToDate(mergeResultRow)
 	if err != nil {
-		cli.Println("merge finished, but failed to check for fast-forward")
 		cli.Println(err.Error())
+		return 1
+	}
+	if upToDate {
+		// Git CLI language.
+		cli.Println("Already up to date.")
 		return 0
 	}
 
-	if len(rows) != 1 {
-		cli.Println("Runtime error: merge operation returned unexpected number of rows: ", len(rows))
+	// if merge is called with '--no-commit', we need to commit the sql transaction or the staged changes will be lost
+	_, _, err = queryist.Query(sqlCtx, "COMMIT")
+	if err != nil {
+		cli.Println(err.Error())
 		return 1
 	}
-	row := rows[0]
 
 	if !apr.Contains(cli.AbortParam) {
 		//todo: refs with the `remotes/` prefix will fail to get a hash
@@ -176,7 +186,7 @@ func (cmd MergeCmd) Exec(ctx context.Context, commandStr string, args []string,
 			cli.Println(mergeHashErr.Error())
 		}
 
-		fastFwd := getFastforward(row, dprocedures.MergeProcFFIndex)
+		fastFwd := getFastforward(mergeResultRow, dprocedures.MergeProcFFIndex)
 
 		if apr.Contains(cli.NoCommitFlag) {
 			return printMergeStats(fastFwd, apr, queryist, sqlCtx, usage, headHash, mergeHash, "HEAD", "STAGED")
@@ -706,3 +716,28 @@ func handleMergeErr(sqlCtx *sql.Context, queryist cli.Queryist, mergeErr error,
 
 	return 0
 }
+
+func everythingUpToDate(row sql.Row) (bool, error) {
+	if row == nil {
+		return false, fmt.Errorf("Runtime error: nil row returned from merge operation")
+	}
+
+	// We don't currently define these in a readily accessible way, so we'll just hard-code the column indexes.
+	// Confident we'll never change these.
+	hashColumn := 0
+	msgColumn := 3
+
+	if hash, ok := row[hashColumn].(string); ok {
+		if msg, ok := row[msgColumn].(string); ok {
+			if hash == "" && msg == "Everything up-to-date" {
+				return true, nil
+			}
+		} else {
+			return false, fmt.Errorf("Runtime error: merge operation returned unexpected message column type: %v", row[msgColumn])
+		}
+	} else {
+		return false, fmt.Errorf("Runtime error: merge operation returned unexpected hash column type: %v", row[hashColumn])
+	}
+
+	return false, nil
+}

integration-tests/bats/shallow-clone.bats

@@ -204,11 +204,12 @@ seed_and_start_serial_remote() {
     [ "$status" -eq 0 ]
 
     cd file-remote
-    dolt checkout -b branch
+    dolt branch other HEAD
 
     dolt checkout main
-
-    dolt merge branch
+    run dolt merge other
+    [ "$status" -eq 0 ]
+    [[ "$output" =~ "Already up to date" ]] || false
 }
 
 @test "shallow-clone: push to a new remote should error" {