Dedupe sqlc.arg parameters wrapped in a type cast for MySQL

When a sqlc.arg() call was wrapped in a CAST (or MySQL's synthetic
MATCH...AGAINST type cast), the resulting Parameter was not marked as
named. Downstream struct-field generation then added numeric suffixes
to disambiguate identical names, producing spurious fields like
SearchTerm_3 alongside SearchTerm.

Capture the isNamed result from FetchMerge so the column correctly
reflects that it came from a named parameter, letting the code
generator reuse a single struct field for repeated sqlc.arg(name)
references.

Fixes #4376

Author: claude

internal/compiler/resolve.go

@@ -513,10 +513,11 @@ func (comp *Compiler) resolveCatalogRefs(qc *QueryCatalog, rvs []*ast.RangeVar,
 			}
 			col := toColumn(n.TypeName)
 			defaultP := named.NewInferredParam(col.Name, col.NotNull)
-			p, _ := params.FetchMerge(ref.ref.Number, defaultP)
+			p, isNamed := params.FetchMerge(ref.ref.Number, defaultP)
 
 			col.Name = p.Name()
 			col.NotNull = p.NotNull()
+			col.IsNamedParam = isNamed
 			a = append(a, Parameter{
 				Number: ref.ref.Number,
 				Column: col,

internal/endtoend/testdata/params_duplicate/mysql/go/models.go

@@ -11,3 +11,8 @@ WHERE first_name = sqlc.arg(name)
 /* name: SelectUserQuestion :many */
 SELECT first_name from
 users where (? = id OR  ? = 0);
+
+/* name: SelectUserByAgeCast :many */
+SELECT first_name FROM users
+WHERE age > CAST(sqlc.arg(threshold) AS SIGNED)
+   OR age < CAST(sqlc.arg(threshold) AS SIGNED);

internal/endtoend/testdata/params_duplicate/mysql/go/query.sql.go

@@ -1,5 +1,6 @@
 CREATE TABLE users (
     id integer NOT NULL AUTO_INCREMENT PRIMARY KEY,
     first_name varchar(255),
-    last_name varchar(255)
+    last_name varchar(255),
+    age int
 ) ENGINE=InnoDB;