replace version alias mechanism with a more flexible rule set, add a …

…bunch of tests

README.md

@@ -41,6 +41,9 @@ the `vendor` folder and generated files.
 - Output is always formatted, `-format` has been removed.
 - The notion of `local` packages with configurable prefixes has been removed,
   configure a set instead. Usually the `project` set will be sufficient.
+- Likewise, the notion of "version aliases" was replaced with a flexible rule system,
+  allowing to configure dynamic aliases for matching packages and rewriting the code
+  accordingly (see below for important notes on this).
 - Configuration happens primarily via the config file `.gimps.yaml`.
 - Many files and directories can be specified as one; the main focus of gimps is not to be
   a goimports/gopls alternative, but to be an addition and useful in CI environments.
@@ -95,11 +98,47 @@ sets:
     patterns:
       - 'k8c.io/**'
       - 'github.com/kubermatic/**'
+
   - name: kubernetes
     patterns:
       - 'k8s.io/**'
       - '*.k8s.io/**'
 
+# gimps can enforce aliases for certain imports. For example, you can ensure
+# that all imports of "k8s.io/api/core/v1" are aliased as "corev1".
+# Rules are processed one at a time and the first matching is applied.
+#
+# There are a few important caveats to note:
+#
+#   * gimps only tokenizes source code and doesn't have deep knowledge of
+#     the semantics. If a package named "foo" is important and a local
+#     function call to `foo.DoSomething()` happens, gimps cannot determine
+#     whether "foo" here is the package or a local variable.
+#     To prevent accidental rewrites, ensure to never name a variable after
+#     any imported package (i.e. don't shadow the package name).
+#   * Rewriting aliases requires to load package dependencies for each
+#     package that is processed. This requires quite a bit of CPU and can
+#     can slow down gimps noticibly. If no rules are configured, gimps
+#     automatically skips loading package dependencies.
+aliasRules:
+  - # a unique name
+    name: k8s-api
+    # a Go regexp, ideally anchored (with ^ and $) to prevent mismatches,
+    # all packages that match will get an alias as configured below.
+    # The example below matches for example "k8s.io/api/core/v1"
+    expr: '^k8s.io/api/([a-z0-9-]+)/(v[a-z0-9-]+)$'
+    # the alias to use for the import; you will most likely always use
+    # references to groups in the expr ($1 gives the first matched group, etc.).
+    # Pay attention to not accidentically generate the same alias for
+    # multiple packages used in the same file (gimps will abort in this case).
+    # With the example package above, the configuration below yields "corev1".
+    alias: '$1$2'
+
+  - name: k8s-apimachinery
+    # contains an optional third subpackage, $4 will be empty if no subpackage was found
+    expr: '^k8s.io/apimachinery/pkg/apis/([a-z0-9-]+)/(v[a-z0-9-]+)(/([a-z0-9-]+))?$'
+    alias: '$1$2$4'
+
 # paths that match any of the following glob expressions (relative to the
 # go.mod) will be ignored; if nothing is configured, the following shows
 # the default configuration.
@@ -146,6 +185,8 @@ only makes sense if you provide exactly one file, otherwise separating the outpu
 
 If you just want to see which files would be fixed, run with `-dry-run`.
 
+Give `-verbose` to show all files being processed instead of just fixed files.
+
 ```bash
 $ cd ~/myproject
 $ gimps .

fs.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"errors"
+	"fmt"
 	"go/parser"
 	"go/token"
 	"io/fs"
@@ -11,7 +12,7 @@ import (
 	"regexp"
 	"strings"
 
-	doublestar "github.com/bmatcuk/doublestar/v4"
+	doublestarx "github.com/bmatcuk/doublestar/v4"
 )
 
 // listFiles takes a filename or directory as its start argument and returns
@@ -24,7 +25,7 @@ func listFiles(start string, moduleRoot string, skips []string) ([]string, error
 
 	info, err := os.Stat(start)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("invalid file: %v", err)
 	}
 
 	if !info.IsDir() {
@@ -34,7 +35,7 @@ func listFiles(start string, moduleRoot string, skips []string) ([]string, error
 	err = filepath.WalkDir(start, func(path string, d fs.DirEntry, err error) error {
 		relPath, err := filepath.Rel(moduleRoot, path)
 		if err != nil {
-			return err
+			return fmt.Errorf("invalid file: %v", err)
 		}
 
 		if isSkipped(relPath, skips) {
@@ -60,7 +61,7 @@ func listFiles(start string, moduleRoot string, skips []string) ([]string, error
 
 func isSkipped(relPath string, skips []string) bool {
 	for _, skip := range skips {
-		if match, _ := doublestar.Match(skip, relPath); match {
+		if match, _ := doublestarx.Match(skip, relPath); match {
 			return true
 		}
 	}
@@ -98,7 +99,7 @@ var (
 func isGeneratedFile(filename string) (bool, error) {
 	content, err := ioutil.ReadFile(filename)
 	if err != nil {
-		return false, err
+		return false, fmt.Errorf("failed to read file: %v", err)
 	}
 
 	return isGeneratedCode(content)
@@ -109,7 +110,7 @@ func isGeneratedCode(sourceCode []byte) (bool, error) {
 
 	file, err := parser.ParseFile(fset, "", sourceCode, parser.ParseComments)
 	if err != nil {
-		return false, err
+		return false, fmt.Errorf("failed to parse code: %v", err)
 	}
 
 	// go through all comments until we reach the package declaration

main.go

@@ -39,10 +39,12 @@ func main() {
 	dryRun := false
 	showVersion := false
 	stdout := false
+	verbose := false
 
 	flag.StringVar(&configFile, "config", configFile, "Path to the config file (mandatory).")
 	flag.BoolVar(&stdout, "stdout", showVersion, "Print output to stdout instead of updating the source file(s).")
 	flag.BoolVar(&dryRun, "dry-run", dryRun, "Do not update files.")
+	flag.BoolVar(&verbose, "verbose", verbose, "List all instead of just changed files.")
 	flag.BoolVar(&showVersion, "version", stdout, "Show version and exit.")
 	flag.Parse()
 
@@ -82,6 +84,11 @@ func main() {
 		config.ProjectName = modName
 	}
 
+	aliaser, err := gimps.NewAliaser(config.ProjectName, config.AliasRules)
+	if err != nil {
+		log.Fatalf("Failed to initialize aliaser: %v", err)
+	}
+
 	for _, input := range inputs {
 		filenames, err := listFiles(input, modRoot, config.Exclude)
 		if err != nil {
@@ -100,21 +107,29 @@ func main() {
 				}
 			}
 
-			formattedOutput, hasChange, err := gimps.Execute(&config.Config, filename)
+			relPath, err := filepath.Rel(modRoot, filename)
+			if err != nil {
+				log.Fatalf("This should never happen, could not determine relative path: %v", err)
+			}
+
+			if verbose {
+				log.Printf("> %s", relPath)
+			}
+
+			formattedOutput, hasChange, err := gimps.Execute(&config.Config, filename, aliaser)
 			if err != nil {
 				log.Fatalf("Failed to process %q: %v", filename, err)
 			}
 
 			if stdout {
 				fmt.Print(string(formattedOutput))
 			} else if hasChange {
-				relPath, err := filepath.Rel(modRoot, filename)
-				if err != nil {
-					log.Fatalf("This should never happen, could not determine relative path: %v", err)
+				if verbose {
+					log.Printf("! %s", relPath)
+				} else {
+					log.Printf("Fixed %s", relPath)
 				}
 
-				log.Printf("Fixing %s", relPath)
-
 				if !dryRun {
 					if err := ioutil.WriteFile(filename, formattedOutput, 0644); err != nil {
 						log.Fatalf("Failed to write fixed result to file %q: %v", filename, err)