From 9fe7122db66196a040928759ea12d8e3cd709f5f Mon Sep 17 00:00:00 2001
From: Qoder-Undefined <133337507+Nanafancy@users.noreply.github.com>
Date: Thu, 25 Jun 2026 21:58:47 +0100
Subject: [PATCH] implemented the missing custom

---
 libs/engine/analyzers/solidity-analyzer.ts    |  17 +++
 .../errors/detect-missing-custom-errors.ts    | 109 ++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 rules/optimization/errors/detect-missing-custom-errors.ts

diff --git a/libs/engine/analyzers/solidity-analyzer.ts b/libs/engine/analyzers/solidity-analyzer.ts
index bd9bd34..adda7b8 100644
--- a/libs/engine/analyzers/solidity-analyzer.ts
+++ b/libs/engine/analyzers/solidity-analyzer.ts
@@ -10,6 +10,7 @@ import {
 } from "../core/analyzer-interface";
 import { detectStorageSlotCollisions } from "../../../rules/security/storage-layout/detect-storage-slot-collisions";
 import { detectMissingImmutable } from "../../../rules/optimization/storage/detect-missing-immutable";
+import { detectMissingCustomErrors } from "../../../rules/optimization/errors/detect-missing-custom-errors";
 
 export class SolidityAnalyzer extends BaseAnalyzer implements Analyzer {
   private rules: Rule[] = [
@@ -226,6 +227,22 @@ export class SolidityAnalyzer extends BaseAnalyzer implements Analyzer {
       },
       documentationUrl: "https://docs.gasguard.dev/rules/sol-017",
     },
+    {
+      id: "sol-018",
+      name: "Missing Custom Errors",
+      description:
+        "Detects revert strings that could be replaced with custom errors for gas efficiency",
+      severity: Severity.MEDIUM,
+      category: "gas-optimization",
+      enabled: true,
+      tags: ["errors", "revert", "gas", "deployment"],
+      estimatedGasImpact: {
+        min: 50,
+        max: 500,
+        typical: 150,
+      },
+      documentationUrl: "https://docs.gasguard.dev/rules/sol-018",
+    },
   ];
 
   getName(): string;
diff --git a/rules/optimization/errors/detect-missing-custom-errors.ts b/rules/optimization/errors/detect-missing-custom-errors.ts
new file mode 100644
index 0000000..f74de33
--- /dev/null
+++ b/rules/optimization/errors/detect-missing-custom-errors.ts
@@ -0,0 +1,109 @@
+/**
+ * Detect Missing Custom Errors
+ *
+ * Detects contracts using revert strings instead of custom errors.
+ * Custom errors are more gas efficient and reduce deployment size.
+ */
+
+export interface MissingCustomError {
+  line: number;
+  message: string;
+  revertString: string;
+}
+
+export interface MissingCustomErrorsResult {
+  detected: boolean;
+  errors: MissingCustomError[];
+  message: string;
+  suggestion: string;
+}
+
+function stripComments(code: string): string {
+  let result = '';
+  let inBlockComment = false;
+  const lines = code.split('\n');
+
+  for (const line of lines) {
+    if (!inBlockComment) {
+      const blockCommentStart = line.indexOf('/*');
+      const blockCommentEnd = line.indexOf('*/');
+
+      if (blockCommentStart !== -1 && blockCommentEnd !== -1 && blockCommentStart < blockCommentEnd) {
+        result += line.substring(0, blockCommentStart) + line.substring(blockCommentEnd + 2);
+      } else if (blockCommentStart !== -1) {
+        inBlockComment = true;
+        result += line.substring(0, blockCommentStart);
+      } else if (line.trim().startsWith('//')) {
+        continue;
+      } else {
+        result += line;
+      }
+    } else {
+      const blockCommentEnd = line.indexOf('*/');
+      if (blockCommentEnd !== -1) {
+        inBlockComment = false;
+        result += line.substring(blockCommentEnd + 2);
+      }
+    }
+  }
+
+  return result;
+}
+
+function hasCustomErrors(code: string): boolean {
+  return /error\s+[A-Za-z_$][\w$]*\s*\([^)]*\)\s*;/.test(code);
+}
+
+function extractRevertStrings(code: string): MissingCustomError[] {
+  const findings: MissingCustomError[] = [];
+  const lines = code.split('\n');
+
+  const revertStringPattern = /(revert\s*\(\s*["'])([^"']+)(["']\s*\)|\.?)|\brequire\s*\(\s*[^,]+,\s*["']([^"']+)["']\s*\)/g;
+
+  for (let i = 0; i < lines.length; i++) {
+    const line = lines[i];
+    const trimmed = line.trim();
+
+    if (trimmed.startsWith('//') || trimmed.startsWith('/*') || trimmed.startsWith('*')) {
+      continue;
+    }
+
+    let match;
+    while ((match = revertStringPattern.exec(line)) !== null) {
+      const revertString = match[2] || match[4];
+      if (revertString) {
+        findings.push({
+          line: i + 1,
+          message: `Revert string "${revertString}" detected. Consider using custom errors for gas efficiency.`,
+          revertString,
+        });
+      }
+    }
+  }
+
+  return findings;
+}
+
+export function detectMissingCustomErrors(code: string): MissingCustomErrorsResult {
+  const strippedCode = stripComments(code);
+  const hasCustomErrorDefinitions = hasCustomErrors(strippedCode);
+  const revertFindings = extractRevertStrings(strippedCode);
+
+  const revertStrings = revertFindings.filter(f => !hasCustomErrorDefinitions);
+
+  if (revertStrings.length === 0) {
+    return {
+      detected: false,
+      errors: [],
+      message: 'No missing custom error opportunities detected.',
+      suggestion: '',
+    };
+  }
+
+  return {
+    detected: true,
+    errors: revertStrings,
+    message: `${revertStrings.length} revert string(s) detected. Consider using custom errors: ${revertStrings.map(e => e.revertString).join(', ')}.`,
+    suggestion: 'Define custom errors using the `error` keyword and use them with `revert CustomError()` instead of revert strings.',
+  };
+}
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