clear warnings better, and separate warning count from actual warnings

Author: James Cor

sql/analyzer/warnings.go

@@ -20,23 +20,25 @@ import (
 	"github.com/dolthub/go-mysql-server/sql/transform"
 )
 
+// clearWarnings resets the warning count to 0 and removes any warnings from the current context.
 func clearWarnings(ctx *sql.Context, a *Analyzer, node sql.Node, scope *plan.Scope, sel RuleSelector, qFlags *sql.QueryFlags) (sql.Node, transform.TreeIdentity, error) {
+	// This is an analyzer rule because we need to clear the warnings from the previous query before executing
+	// the current query, except for the case of `show warnings` which should not clear the warnings.
 	children := node.Children()
 	if len(children) == 0 {
 		return node, transform.SameTree, nil
 	}
 
 	switch ch := children[0].(type) {
+	case *plan.Offset, *plan.Limit:
+		// `show warning limit x offset y` is valid, so we need to recurse
+		return clearWarnings(ctx, a, ch, scope, sel, qFlags)
 	case plan.ShowWarnings:
+		// ShowWarnings should not clear the warnings, but should still reset the warning count.
+		ctx.ClearWarningCount()
 		return node, transform.SameTree, nil
-	case *plan.Offset:
-		clearWarnings(ctx, a, ch, scope, sel, qFlags)
-		return node, transform.SameTree, nil
-	case *plan.Limit:
-		clearWarnings(ctx, a, ch, scope, sel, qFlags)
+	default:
+		ctx.ClearWarnings()
 		return node, transform.SameTree, nil
 	}
-
-	ctx.ClearWarnings()
-	return node, transform.SameTree, nil
 }

sql/base_session.go

@@ -41,7 +41,7 @@ type BaseSession struct {
 	viewReg          *ViewRegistry
 	warnings         []*Warning
 	warningLock      bool
-	warncnt          uint16
+	warningCount     uint16 // num of warnings from recent query; does not always equal to len(warnings)
 	locks            map[string]bool
 	queriedDb        string
 	lastQueryInfo    map[string]*atomic.Value
@@ -331,6 +331,7 @@ func (s *BaseSession) SetConnectionId(id uint32) {
 // Warn stores the warning in the session.
 func (s *BaseSession) Warn(warn *Warning) {
 	s.warnings = append(s.warnings, warn)
+	s.warningCount = uint16(len(s.warnings))
 }
 
 // Warnings returns a copy of session warnings (from the most recent - the last one)
@@ -354,25 +355,25 @@ func (s *BaseSession) UnlockWarnings() {
 	s.warningLock = false
 }
 
+// ClearWarningCount cleans up session warnings
+func (s *BaseSession) ClearWarningCount() {
+	s.warningCount = 0
+}
+
 // ClearWarnings cleans up session warnings
 func (s *BaseSession) ClearWarnings() {
 	if s.warningLock {
 		return
 	}
-	cnt := uint16(len(s.warnings))
-	if s.warncnt != cnt {
-		s.warncnt = cnt
-		return
-	}
 	if s.warnings != nil {
 		s.warnings = s.warnings[:0]
 	}
-	s.warncnt = 0
+	s.ClearWarningCount()
 }
 
 // WarningCount returns a number of session warnings
 func (s *BaseSession) WarningCount() uint16 {
-	return uint16(len(s.warnings))
+	return s.warningCount
 }
 
 // AddLock adds a lock to the set of locks owned by this user which will need to be released if this session terminates

sql/session.go

@@ -104,6 +104,8 @@ type Session interface {
 	Warn(warn *Warning)
 	// Warnings returns a copy of session warnings (from the most recent).
 	Warnings() []*Warning
+	// ClearWarnCount clears the warning count without clearing the actual warnings.
+	ClearWarningCount()
 	// ClearWarnings cleans up session warnings.
 	ClearWarnings()
 	// WarningCount returns a number of session warnings