feat: Add automatic error comparison and type assertion fixes (#96)

Signed-off-by: Kemal Akkoyun <[email protected]>
Co-authored-by: ccoVeille <[email protected]>

Enhance errorlint analyzer with automatic fixes for:
- Error comparisons using `==` and `!=`
- Type assertions on errors
- Error switches

Adds suggested fixes to:
- Replace direct error comparisons with `errors.Is()`
- Convert type assertions to use `errors.As()`
- Transform error switches to use `errors.Is()` and `errors.As()`

Includes new test cases and golden files to validate the new automatic fixing capabilities.

* feat: Improve errorlint with better variable naming and error handling

- Add function for meaningful error variable names
- Preserve original "ok" variable names in type assertions
- Use errors.As() with generated variable names
- Add tests for custom and wrapped errors

Author: kakkoyun

README.md

@@ -24,6 +24,24 @@ go-errorlint ./...
 ```
 If there are one or more results, the exit status is set to `1`.
 
+To automatically fix issues where possible, use the `-fix` flag:
+```
+go-errorlint -fix ./...
+```
+
+The tool can automatically fix:
+
+> [!CAUTION]
+> These fixes are still under development and the behavior is not yet stable.
+> It is possible that it will make mistakes and cause more harm than good.
+> Use with caution.
+
+1. Non-wrapping format verb for fmt.Errorf (changing `%v` to `%w`)
+2. Direct error comparisons (replacing `err == ErrFoo` with `errors.Is(err, ErrFoo)`)
+3. Type assertions on errors (replacing `err.(*MyError)` with `errors.As` usage)
+
+Complex cases like switches on errors or type switches cannot be automatically fixed.
+
 
 ## Examples
 
@@ -70,6 +88,8 @@ Errors returned from standard library functions that explicitly document that
 an unwrapped error is returned are allowed by the linter. Notable cases are
 `io.EOF` and `sql.ErrNoRows`.
 
+You can pass `-fix` to have go-errorlint automatically fix these issues for you.
+
 **Caveats**:
 * Comparing the error returned from `(io.Reader).Read` to `io.EOF` without
   `errors.Is` is considered valid as this is
@@ -95,6 +115,8 @@ var me MyError
 ok := errors.As(err, &me)
 ```
 
+You can pass `-fix` to have go-errorlint automatically fix these issues for you.
+
 ## Contributing
 
 Do you think you have found a bug? Then please report it via the Github issue tracker. Make sure to

errorlint/analysis_test.go

@@ -43,3 +43,13 @@ func TestIssueRegressions(t *testing.T) {
 	analyzer := NewAnalyzer()
 	analysistest.Run(t, analysistest.TestData(), analyzer, "issues")
 }
+
+func TestErrorComparisonFixes(t *testing.T) {
+	analyzer := NewAnalyzer()
+	analysistest.RunWithSuggestedFixes(t, analysistest.TestData(), analyzer, "errorcompare")
+}
+
+func TestErrorTypeAssertionFixes(t *testing.T) {
+	analyzer := NewAnalyzer()
+	analysistest.RunWithSuggestedFixes(t, analysistest.TestData(), analyzer, "errorassert")
+}