Add "no-self-import" rule

docs/no-self-import.md

@@ -0,0 +1,27 @@
+# no-self-import
+
+A package should not import components of itself using a globally-qualified name; it should use relative imports instead.
+
+**Bad**:
+
+```ts
+import foo from "this-package/foo.d.ts";
+```
+
+**Good**:
+
+```ts
+import foo from "./foo.d.ts";
+```
+
+**Bad**:
+
+```ts
+import myself from "this-package";
+```
+
+**Good**:
+
+```ts
+import myself from ".";
+```

dt.json

@@ -2,6 +2,7 @@
 	"extends": "./dtslint.json",
 	"rules": {
 		"dt-header": true,
-		"no-bad-reference": true
+		"no-bad-reference": true,
+		"no-self-import": true
 	}
 }

src/rules/noSelfImportRule.ts

@@ -0,0 +1,50 @@
+import { basename, dirname } from "path";
+
+import * as Lint from "tslint";
+import * as ts from "typescript";
+
+import { failure } from "../util";
+
+export class Rule extends Lint.Rules.TypedRule {
+	static metadata: Lint.IRuleMetadata = {
+		ruleName: "no-self-import",
+		description: "Forbids declaration files to import the current package using a global import.",
+		optionsDescription: "Not configurable.",
+		options: null,
+		type: "functionality",
+		typescriptOnly: false,
+	};
+
+	applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
+		if (!sourceFile.isDeclarationFile) {
+			return [];
+		}
+
+		const name = getCommonDirectoryName(program.getSourceFiles());
+		return this.applyWithFunction(sourceFile, ctx => walk(ctx, name));
+	}
+}
+
+const FAILURE_STRING = failure(
+	Rule.metadata.ruleName,
+	"Declaration file should not use a global import of itself. Use a relative import.");
+
+function getCommonDirectoryName(files: ReadonlyArray<ts.SourceFile>): string {
+	let minLen = 999;
+	let minDir = "";
+	for (const file of files) {
+		const dir = dirname(file.fileName);
+		if (dir.length < minLen) {
+			minDir = dir;
+		}
+	}
+	return basename(minDir);
+}
+
+function walk(ctx: Lint.WalkContext<void>, packageName: string): void {
+	for (const i of ctx.sourceFile.imports) {
+		if (i.text === packageName || i.text.startsWith(packageName + "/")) {
+			ctx.addFailureAtNode(i, FAILURE_STRING);
+		}
+	}
+}