fix: Let column names not result in invalid Go field names

Column names are less restricted than Go struct field names, which
should be proper Go identifiers. Hence, column names cannot be
translated directly into field names. This commit tries to address
this.

Characters in column names that do not qualify as a Go identifier
are stripped. The title casing as applied to underscores is applied
to stripped characters.

Author: rollulus

internal/codegen/golang/struct.go

@@ -20,6 +20,15 @@ func StructName(name string, settings *plugin.Settings) string {
 		return rename
 	}
 	out := ""
+	name = strings.Map(func(r rune) rune {
+		if unicode.IsLetter(r) {
+			return r
+		}
+		if unicode.IsDigit(r) {
+			return r
+		}
+		return rune('_')
+	}, name)
 	for _, p := range strings.Split(name, "_") {
 		if p == "id" {
 			out += "ID"

internal/endtoend/testdata/codegen_struct_field_names/stdlib/README.md

@@ -0,0 +1 @@
+This tests that Go struct field names are proper Go identifiers.

internal/endtoend/testdata/codegen_struct_field_names/stdlib/go/db.go

@@ -0,0 +1,7 @@
+CREATE TABLE bar (
+    id INT NOT NULL,
+    "!!!nobody,_,-would-believe---this-...?!" INT,
+    "parent        id" INT);
+
+-- name: test :one
+SELECT * from bar limit 1;

internal/endtoend/testdata/codegen_struct_field_names/stdlib/go/models.go

@@ -0,0 +1,11 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}