Fence a function that spells a method

naming_test.go

@@ -0,0 +1,46 @@
+package fejkdata
+
+import (
+	"go/ast"
+	"sort"
+	"testing"
+)
+
+// TestNoFunctionSpellsAMethod holds a call to one unit. A method is written with
+// its receiver and a function bare, so one name on both reads alike at a call site
+// and greps as one unit; two types may share a method name, since the receiver
+// standing before it says which.
+func TestNoFunctionSpellsAMethod(t *testing.T) {
+	_, files := sourceFiles(t)
+	funcs, methods := declaredCalls(files)
+	names := make([]string, 0, len(funcs))
+	for name := range funcs {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	for _, name := range names {
+		if recv := methods[name]; recv != "" {
+			t.Errorf("func %s and %s.%s are two units under one name; name them apart", name, recv, name)
+		}
+	}
+}
+
+// declaredCalls is every name the package declares as a function, and every name
+// it declares as a method with one type declaring it.
+func declaredCalls(files []*ast.File) (funcs map[string]bool, methods map[string]string) {
+	funcs, methods = map[string]bool{}, map[string]string{}
+	for _, f := range files {
+		for _, decl := range f.Decls {
+			d, isFunc := decl.(*ast.FuncDecl)
+			if !isFunc {
+				continue
+			}
+			if recv := receiverType(d.Recv); recv != "" {
+				methods[d.Name.Name] = recv
+				continue
+			}
+			funcs[d.Name.Name] = true
+		}
+	}
+	return funcs, methods
+}