testdata/issues, wit/bindgen: test for #242

Predeclare Tag method on variant types.

Author: ydnar

testdata/issues/issue242.wit

@@ -0,0 +1,15 @@
+package issues:issue242;
+
+interface i {
+	variant v {
+		a,
+		b,
+		// tag might collide with (cm.Variant).Tag() method
+		tag,
+		%string(string),
+	}
+}
+
+world w {
+	import i;
+}

testdata/issues/issue242.wit.json

@@ -0,0 +1,70 @@
+{
+  "worlds": [
+    {
+      "name": "w",
+      "imports": {
+        "interface-0": {
+          "interface": {
+            "id": 0
+          }
+        }
+      },
+      "exports": {},
+      "package": 0
+    }
+  ],
+  "interfaces": [
+    {
+      "name": "i",
+      "types": {
+        "v": 0
+      },
+      "functions": {},
+      "package": 0
+    }
+  ],
+  "types": [
+    {
+      "name": "v",
+      "kind": {
+        "variant": {
+          "cases": [
+            {
+              "name": "a",
+              "type": null
+            },
+            {
+              "name": "b",
+              "type": null
+            },
+            {
+              "name": "tag",
+              "type": null,
+              "docs": {
+                "contents": "tag might collide with (cm.Variant).Tag() method"
+              }
+            },
+            {
+              "name": "string",
+              "type": "string"
+            }
+          ]
+        }
+      },
+      "owner": {
+        "interface": 0
+      }
+    }
+  ],
+  "packages": [
+    {
+      "name": "issues:issue242",
+      "interfaces": {
+        "i": 0
+      },
+      "worlds": {
+        "w": 0
+      }
+    }
+  ]
+}

testdata/issues/issue242.wit.json.golden.wit

@@ -0,0 +1,15 @@
+package issues:issue242;
+
+interface i {
+	variant v {
+		a,
+		b,
+		/// tag might collide with (cm.Variant).Tag() method
+		tag,
+		%string(string),
+	}
+}
+
+world w {
+	import i;
+}

wit/bindgen/generator.go

@@ -539,8 +539,11 @@ func (g *generator) declareTypeDef(file *gen.File, dir wit.Direction, t *wit.Typ
 
 	// Predeclare reserved methods.
 	switch t.Kind.(type) {
+	case *wit.Enum:
+		decl.scope.DeclareName("String") // For fmt.Stringer
 	case *wit.Variant:
-		decl.scope.DeclareName("Tag")
+		decl.scope.DeclareName("Tag")    // Method on cm.Variant
+		decl.scope.DeclareName("String") // For fmt.Stringer
 	}
 
 	return decl, nil
@@ -836,7 +839,6 @@ func (g *generator) variantRep(file *gen.File, dir wit.Direction, t *wit.TypeDef
 
 	decl, _ := g.typeDecl(dir, t)
 	scope := decl.scope
-	scope.DeclareName("String") // For fmt.Stringer
 
 	// Emit type
 	var b strings.Builder