feat(signals): classify build and CI configuration files in path-matchers (#561)

src/signals/path-matchers.ts

@@ -54,9 +54,37 @@
   "build.gradle.kts",
   "pom.xml",
 ]);
 
 const DOCS_EXTENSIONS: ReadonlySet<string> = new Set(["md", "mdx", "markdown", "rst", "adoc", "asciidoc"]);
 
+// Exact basenames (lowercased) that are unambiguously build/CI config files regardless of directory.
+const CONFIG_FILE_NAMES: ReadonlySet<string> = new Set([
+  "dockerfile",
+  "makefile",
+  ".editorconfig",
+  ".nvmrc",
+  ".npmrc",
+  ".browserslistrc",
+]);
+
+// Filename prefixes that identify build, lint, test-runner, and environment config files.
+const CONFIG_FILE_PREFIXES: readonly string[] = [
+  "tsconfig",
+  "jsconfig",
+  "jest.config",
+  "vitest.config",
+  "vite.config",
+  "webpack.config",
+  "rollup.config",
+  "postcss.config",
+  "tailwind.config",
+  "next.config",
+  ".env",
+  ".eslint",
+  ".prettier",
+  ".babel",
+];
+
 /** Machine-generated output (codegen, protobuf, source maps, typegen). */
 export function isGeneratedFile(path: string): boolean {
   const norm = normalize(path);
@@ -97,6 +125,20 @@
   return DEPENDENCY_MANIFEST_NAMES.has(basename(path));
 }
 
+/**
+ * Build, lint, test-runner, and environment configuration files. Distinct from dependency manifests
+ * (which declare external dependencies) and source code. Config-only diffs are lower-effort than
+ * genuine source changes, so slop signals can weight them differently (#561).
+ */
+export function isConfigFile(path: string): boolean {
+  const base = basename(path);
+  if (CONFIG_FILE_NAMES.has(base)) return true;
+  if (CONFIG_FILE_PREFIXES.some((prefix) => base.startsWith(prefix))) return true;
+  if (/\.(config|rc)\.[a-z0-9]+$/i.test(base)) return true;
+  // `.stylelintrc`-style: dot-prefixed name with no extension after "rc"; `custom.rc`: dotted rc extension.
+  return base.endsWith(".rc") || /^\.[^.]+rc$/i.test(base);
+}
+
 /**
  * Files that masquerade as substantive source/work but are machine-produced or imported — the set a
  * padded diff inflates its size with. Lockfiles, dependency manifests, and docs are legitimate change
@@ -112,6 +154,7 @@
   | "vendored"
   | "lockfile"
   | "dependency_manifest"
+  | "config"
   | "test"
   | "docs"
   | "source"
@@ -128,6 +171,7 @@
   if (isVendoredFile(path)) return "vendored";
   if (isLockfile(path)) return "lockfile";
   if (isDependencyManifestFile(path)) return "dependency_manifest";
+  if (isConfigFile(path)) return "config";
   if (isTestFile(path) || isTestPath(path)) return "test";
   if (isDocsFile(path)) return "docs";
   if (isCodeFile(path)) return "source";

test/unit/path-matchers.test.ts

@@ -1,7 +1,8 @@
 import { describe, expect, it } from "vitest";
 import {
   classifyChangedFile,
   isDependencyManifestFile,
+  isConfigFile,
   isDocsFile,
   isGeneratedFile,
   isLockfile,
@@ -140,6 +141,38 @@
   });
 });
 
+describe("isConfigFile", () => {
+  it("matches config files by exact basename (case-insensitive)", () => {
+    for (const path of ["Dockerfile", "frontend/Makefile", ".editorconfig", "ci/.nvmrc", ".npmrc"]) {
+      expect(isConfigFile(path)).toBe(true);
+    }
+  });
+
+  it("matches config files by known filename prefix", () => {
+    for (const path of ["tsconfig.build.json", "vitest.config.ts", ".env.local", ".eslintrc.json", ".prettierrc.js"]) {
+      expect(isConfigFile(path)).toBe(true);
+    }
+  });
+
+  it("matches config files by the .config.ext or .rc.ext pattern", () => {
+    for (const path of ["babel.config.cjs", "stylelint.config.mjs", "lint-staged.rc.js"]) {
+      expect(isConfigFile(path)).toBe(true);
+    }
+  });
+
+  it("matches bare .rc suffix config files", () => {
+    for (const path of [".stylelintrc", ".huskyrc", "config/custom.rc"]) {
+      expect(isConfigFile(path)).toBe(true);
+    }
+  });
+
+  it("does not classify source, test, doc, or lockfiles as config", () => {
+    for (const path of ["src/app.ts", "README.md", "package.json", "package-lock.json", "test/unit/app.test.ts"]) {
+      expect(isConfigFile(path)).toBe(false);
+    }
+  });
+});
+
 describe("classifyChangedFile", () => {
   it("classifies each representative path into its category", () => {
     const cases: Array<[string, ReturnType<typeof classifyChangedFile>]> = [
@@ -148,6 +181,8 @@
       ["vendor/lib.go", "vendored"],
       ["package-lock.json", "lockfile"],
       ["package.json", "dependency_manifest"],
+      ["tsconfig.json", "config"],
+      ["vitest.config.ts", "config"],
       ["test/unit/app.test.ts", "test"],
       ["README.md", "docs"],
       ["src/app.ts", "source"],
@@ -158,9 +193,10 @@
     }
   });
 
-  it("prioritizes padding categories over test/source so they are never counted as effort", () => {
+  it("prioritizes padding categories over config/test/source so they are never counted as effort", () => {
     expect(classifyChangedFile("__generated__/schema.test.ts")).toBe("generated");
     expect(classifyChangedFile("vendor/pkg/index.test.js")).toBe("vendored");
     expect(classifyChangedFile("dist/bundle.min.js")).toBe("minified");
+    expect(classifyChangedFile("vendor/tsconfig.json")).toBe("vendored");
   });
 });