From e192e488c3a6a05db1a60cfedf770d8b7761b39c Mon Sep 17 00:00:00 2001
From: Felix Rieseberg <f@anthropic.com>
Date: Sat, 28 Jun 2025 16:11:32 -0700
Subject: [PATCH] feat: Negation patterns (#24)

---
 src/node/files.ts      | 113 ++++++++++++++++++++++++++---------------
 test/dxtignore.test.ts |  56 ++++++++++++++++++++
 2 files changed, 127 insertions(+), 42 deletions(-)

diff --git a/src/node/files.ts b/src/node/files.ts
index cf17e1f..1491ede 100644
--- a/src/node/files.ts
+++ b/src/node/files.ts
@@ -60,60 +60,89 @@ export function readDxtIgnorePatterns(baseDir: string): string[] {
   }
 }
 
+/**
+ * Tests if a file path matches a given pattern
+ */
+function matchesPattern(
+  pattern: string,
+  filePath: string,
+  fileName: string,
+): boolean {
+  if (pattern.includes("*")) {
+    // Enhanced glob matching to handle directory paths like "temp/*"
+    let patternToMatch = pattern;
+
+    // Handle patterns like "dir/" by converting to "dir/**"
+    if (pattern.endsWith("/")) {
+      patternToMatch = pattern + "**";
+    }
+
+    // Convert glob pattern to regex, with case sensitivity
+    const regexPattern =
+      "^" +
+      patternToMatch
+        .replace(/\./g, "\\.") // Escape dots
+        .replace(/\*\*/g, ".*") // ** matches anything including /
+        .replace(/\*/g, "[^/]*") + // * matches anything except /
+      "$";
+
+    const regex = new RegExp(regexPattern);
+
+    // Test full path
+    if (regex.test(filePath)) return true;
+
+    // Test filename
+    if (regex.test(fileName)) return true;
+
+    // Check if any part of the path matches for patterns like "node_modules"
+    const pathParts = filePath.split(sep);
+    for (const part of pathParts) {
+      if (regex.test(part)) return true;
+    }
+  } else {
+    // Exact match
+    if (fileName === pattern) return true;
+
+    // Check if any part of the path matches
+    if (filePath.includes(pattern)) return true;
+
+    // Handle directory patterns like "tests/"
+    if (pattern.endsWith("/") && filePath.startsWith(pattern)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 export function shouldExclude(
   filePath: string,
   additionalPatterns: string[] = [],
 ): boolean {
   const fileName = basename(filePath);
   const allPatterns = [...EXCLUDE_PATTERNS, ...additionalPatterns];
+  const negationPatterns = allPatterns.filter((p) => p.startsWith("!"));
+  const exclusionPatterns = allPatterns.filter((p) => !p.startsWith("!"));
 
-  for (const pattern of allPatterns) {
-    if (pattern.includes("*")) {
-      // Enhanced glob matching to handle directory paths like "temp/*"
-      let patternToMatch = pattern;
+  let shouldExcludeFile = false;
+  for (const pattern of exclusionPatterns) {
+    if (matchesPattern(pattern, filePath, fileName)) {
+      shouldExcludeFile = true;
+      break;
+    }
+  }
 
-      // Handle patterns like "dir/" by converting to "dir/**"
-      if (pattern.endsWith("/")) {
-        patternToMatch = pattern + "**";
-      }
-
-      // Convert glob pattern to regex, with case sensitivity
-      const regexPattern =
-        "^" +
-        patternToMatch
-          .replace(/\./g, "\\.") // Escape dots
-          .replace(/\*\*/g, ".*") // ** matches anything including /
-          .replace(/\*/g, "[^/]*") + // * matches anything except /
-        "$";
-
-      const regex = new RegExp(regexPattern);
-
-      // Test full path
-      if (regex.test(filePath)) return true;
-
-      // Test filename
-      if (regex.test(fileName)) return true;
-
-      // Check if any part of the path matches for patterns like "node_modules"
-      const pathParts = filePath.split(sep);
-      for (const part of pathParts) {
-        if (regex.test(part)) return true;
-      }
-    } else {
-      // Exact match
-      if (fileName === pattern) return true;
-
-      // Check if any part of the path matches
-      if (filePath.includes(pattern)) return true;
-
-      // Handle directory patterns like "tests/"
-      if (pattern.endsWith("/") && filePath.startsWith(pattern)) {
-        return true;
+  // If excluded, check if any negation pattern un-excludes it
+  if (shouldExcludeFile) {
+    for (const pattern of negationPatterns) {
+      const negatedPattern = pattern.slice(1);
+      if (matchesPattern(negatedPattern, filePath, fileName)) {
+        // File should not be excluded (negation pattern matched)
+        return false;
       }
     }
   }
 
-  return false;
+  return shouldExcludeFile;
 }
 
 export function getAllFiles(
diff --git a/test/dxtignore.test.ts b/test/dxtignore.test.ts
index f5ebe4c..762aaa3 100644
--- a/test/dxtignore.test.ts
+++ b/test/dxtignore.test.ts
@@ -258,4 +258,60 @@ coverage/`;
       );
     });
   });
+
+  describe("Negation patterns", () => {
+    it("should include files that match negation patterns", () => {
+      const additionalPatterns = ["*.log", "!important.log"];
+
+      // debug.log should be excluded (matches *.log, no negation)
+      expect(shouldExclude("debug.log", additionalPatterns)).toBe(true);
+
+      // important.log should NOT be excluded (matches *.log, but negated by !important.log)
+      expect(shouldExclude("important.log", additionalPatterns)).toBe(false);
+
+      // Other files should not be excluded
+      expect(shouldExclude("main.js", additionalPatterns)).toBe(false);
+    });
+
+    it("should handle multiple negation patterns", () => {
+      const additionalPatterns = ["*.log", "!important.log", "!critical.log"];
+
+      expect(shouldExclude("debug.log", additionalPatterns)).toBe(true);
+      expect(shouldExclude("important.log", additionalPatterns)).toBe(false);
+      expect(shouldExclude("critical.log", additionalPatterns)).toBe(false);
+      expect(shouldExclude("other.log", additionalPatterns)).toBe(true);
+    });
+
+    it("should handle negation with glob patterns", () => {
+      const additionalPatterns = ["temp/*", "!temp/important.txt"];
+
+      expect(shouldExclude("temp/debug.txt", additionalPatterns)).toBe(true);
+      expect(shouldExclude("temp/important.txt", additionalPatterns)).toBe(
+        false,
+      );
+      expect(shouldExclude("other/file.txt", additionalPatterns)).toBe(false);
+    });
+
+    it("should handle negation with directory patterns", () => {
+      const additionalPatterns = ["tests/", "!tests/critical/"];
+
+      expect(shouldExclude("tests/unit/test.js", additionalPatterns)).toBe(
+        true,
+      );
+      expect(shouldExclude("tests/critical/test.js", additionalPatterns)).toBe(
+        false,
+      );
+      expect(shouldExclude("src/main.js", additionalPatterns)).toBe(false);
+    });
+
+    it("should not negate files that don't match exclusion patterns", () => {
+      const additionalPatterns = ["*.log", "!main.js"];
+
+      // main.js should not be excluded (doesn't match *.log, negation doesn't apply)
+      expect(shouldExclude("main.js", additionalPatterns)).toBe(false);
+
+      // debug.log should be excluded (matches *.log, no applicable negation)
+      expect(shouldExclude("debug.log", additionalPatterns)).toBe(true);
+    });
+  });
 });