fix(engine/sqlite): support CASE expr (#2926)

Fixes #2925
Fixes #2736

Author: orisano

internal/endtoend/testdata/case_named_params/sqlite/go/db.go

@@ -0,0 +1,6 @@
+-- name: ListAuthors :one
+SELECT  *
+FROM    authors
+WHERE   email = CASE WHEN sqlc.arg(email) = '' then NULL else sqlc.arg(email) END
+        OR username = CASE WHEN sqlc.arg(username) = '' then NULL else sqlc.arg(username) END
+LIMIT   1;

internal/endtoend/testdata/case_named_params/sqlite/go/models.go

@@ -0,0 +1,8 @@
+CREATE TABLE authors (
+  id   INTEGER PRIMARY KEY,
+  username TEXT NULL,
+  email TEXT NULL,
+  name TEXT  NOT NULL,
+  bio  TEXT
+);
+

internal/endtoend/testdata/case_named_params/sqlite/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+	"version": "1",
+	"packages": [
+		{
+			"path": "go",
+			"engine": "sqlite",
+			"name": "querytest",
+			"schema": "schema.sql",
+			"queries": "query.sql"
+		}
+	]
+}

internal/endtoend/testdata/case_named_params/sqlite/query.sql

@@ -1096,6 +1096,28 @@ func (c *cc) convertCollateExpr(n *parser.Expr_collateContext) ast.Node {
 	}
 }
 
+func (c *cc) convertCase(n *parser.Expr_caseContext) ast.Node {
+	e := &ast.CaseExpr{
+		Args: &ast.List{},
+	}
+	es := n.AllExpr()
+	if n.ELSE_() != nil {
+		e.Defresult = c.convert(es[len(es)-1])
+		es = es[:len(es)-1]
+	}
+	if len(es)%2 == 1 {
+		e.Arg = c.convert(es[0])
+		es = es[1:]
+	}
+	for i := 0; i < len(es); i += 2 {
+		e.Args.Items = append(e.Args.Items, &ast.CaseWhen{
+			Expr:   c.convert(es[i+0]),
+			Result: c.convert(es[i+1]),
+		})
+	}
+	return e
+}
+
 func (c *cc) convert(node node) ast.Node {
 	switch n := node.(type) {
 
@@ -1184,6 +1206,9 @@ func (c *cc) convert(node node) ast.Node {
 	case *parser.Expr_castContext:
 		return c.convertCastExpr(n)
 
+	case *parser.Expr_caseContext:
+		return c.convertCase(n)
+
 	default:
 		return todo("convert(case=default)", n)
 	}