/sql/rowexec: attempt to fix panic

sql/rowexec/builder.go

@@ -15,6 +15,7 @@
 package rowexec
 
 import (
+	"fmt"
 	"runtime/trace"
 
 	"github.com/dolthub/go-mysql-server/sql"
@@ -35,13 +36,36 @@ type BaseBuilder struct {
 	override sql.NodeExecBuilder
 }
 
+// panicSafeExecBuilder wraps another sql.NodeExecBuilder and converts panics to errors,
+// preventing server-wide crashes when integrator-provided builders panic.
+type panicSafeExecBuilder struct {
+	inner sql.NodeExecBuilder
+}
+
+func newPanicSafeExecBuilder(inner sql.NodeExecBuilder) sql.NodeExecBuilder {
+	if inner == nil {
+		return nil
+	}
+	return &panicSafeExecBuilder{inner: inner}
+}
+
+func (p *panicSafeExecBuilder) Build(ctx *sql.Context, n sql.Node, r sql.Row) (iter sql.RowIter, err error) {
+	defer func() {
+		if rec := recover(); rec != nil {
+			err = fmt.Errorf("exec builder panic: %v", rec)
+			iter = nil
+		}
+	}()
+	return p.inner.Build(ctx, n, r)
+}
+
 func (b *BaseBuilder) Build(ctx *sql.Context, n sql.Node, r sql.Row) (sql.RowIter, error) {
 	defer trace.StartRegion(ctx, "ExecBuilder.Build").End()
 	return b.buildNodeExec(ctx, n, r)
 }
 
 func NewOverrideBuilder(override sql.NodeExecBuilder) sql.NodeExecBuilder {
-	return &BaseBuilder{override: override}
+	return &BaseBuilder{override: newPanicSafeExecBuilder(override)}
 }
 
 // FinalizeIters applies the final transformations on sql.RowIter before execution.

sql/rowexec/merge_join.go

@@ -47,9 +47,8 @@ func newMergeJoinIter(ctx *sql.Context, b sql.NodeExecBuilder, j *plan.JoinNode,
 	}
 
 	fullRow := make(sql.Row, len(row)+len(j.Left().Schema())+len(j.Right().Schema()))
-	fullRow[0] = row
 	if len(row) > 0 {
-		copy(fullRow[0:], row[:])
+		copy(fullRow, row)
 	}
 
 	// a merge join's first filter provides direction information
@@ -72,14 +71,21 @@ func newMergeJoinIter(ctx *sql.Context, b sql.NodeExecBuilder, j *plan.JoinNode,
 	}
 
 	var iter sql.RowIter = &mergeJoinIter{
-		left:        l,
-		right:       r,
-		filters:     filters[1:],
-		cmp:         cmp,
-		typ:         j.Op,
-		fullRow:     fullRow,
-		scopeLen:    j.ScopeLen,
-		parentLen:   len(row) - j.ScopeLen,
+		left:     l,
+		right:    r,
+		filters:  filters[1:],
+		cmp:      cmp,
+		typ:      j.Op,
+		fullRow:  fullRow,
+		scopeLen: j.ScopeLen,
+		// parentLen is the portion of the parent row beyond the current scope.
+		// Clamp to zero to avoid negative offsets when scopeLen > len(row).
+		parentLen: func() int {
+			if len(row) >= j.ScopeLen {
+				return len(row) - j.ScopeLen
+			}
+			return 0
+		}(),
 		leftRowLen:  len(j.Left().Schema()),
 		rightRowLen: len(j.Right().Schema()),
 		isReversed:  j.IsReversed,

sql/rowexec/node_builder.gen.go

@@ -28,9 +28,11 @@ func (b *BaseBuilder) buildNodeExec(ctx *sql.Context, n sql.Node, row sql.Row) (
 	var err error
 	if b.override != nil {
 		iter, err = b.override.Build(ctx, n, row)
-	}
-	if err != nil {
-		return nil, err
+		if err != nil {
+			// If the override fails, fall back to the default builder
+			iter = nil
+			err = nil
+		}
 	}
 	if iter == nil {
 		iter, err = b.buildNodeExecNoAnalyze(ctx, n, row)