fix(mysql): Handle simplified CASE statements (#2852)

MySQL and PostgreSQL now have the same behavior, generating a nullable string parameter. That behavior isn't right, as we'd expect the parameter to be a boolean. This can be fixed by using a type case or the new annotations in #2800.

Fixes #2847

internal/endtoend/testdata/case_value_param/issue.md

@@ -0,0 +1 @@
+https://github.com/sqlc-dev/sqlc/issues/2847

internal/endtoend/testdata/case_value_param/mysql/query.sql

@@ -0,0 +1,3 @@
+-- name: Update :exec
+UPDATE testing
+SET value = CASE ? WHEN true THEN 'Hello' WHEN false THEN 'Goodbye' ELSE value END;

internal/endtoend/testdata/case_value_param/mysql/schema.sql

@@ -0,0 +1,4 @@
+CREATE TABLE testing (
+  id    int PRIMARY KEY,
+  value text
+);

internal/endtoend/testdata/case_value_param/mysql/sqlc.yaml

@@ -0,0 +1,9 @@
+version: "2"
+sql:
+  - engine: "mysql"
+    schema: "schema.sql"
+    queries: "query.sql"
+    gen:
+      go:
+        package: "querytest"
+        out: "go"

internal/endtoend/testdata/case_value_param/postgresql/query.sql

@@ -0,0 +1,3 @@
+-- name: Update :exec
+UPDATE testing
+SET value = CASE $1 WHEN true THEN 'Hello' WHEN false THEN 'Goodbye' ELSE value END;

internal/endtoend/testdata/case_value_param/postgresql/schema.sql

@@ -0,0 +1,4 @@
+CREATE TABLE testing (
+  id    int PRIMARY KEY,
+  value text
+);

internal/endtoend/testdata/case_value_param/postgresql/sqlc.yaml

@@ -0,0 +1,10 @@
+version: "2"
+sql:
+  - engine: "postgresql"
+    schema: "schema.sql"
+    queries: "query.sql"
+    gen:
+      go:
+        package: "querytest"
+        out: "go"
+        sql_package: "pgx/v5"

internal/engine/dolphin/convert.go

@@ -745,6 +745,7 @@ func (c *cc) convertCaseExpr(n *pcast.CaseExpr) ast.Node {
 		list.Items = append(list.Items, c.convertWhenClause(n))
 	}
 	return &ast.CaseExpr{
+		Arg:       c.convert(n.Value),
 		Args:      list,
 		Defresult: c.convert(n.ElseClause),
 		Location:  n.OriginTextPosition(),