feat: add a "LICENSE" file to Dart packages. (#1977)

pub.dev requires that packages have a LICENSE file in their root.

The file was named "LICENSE.txt.mustache" because `WalkTemplatesDir`
elides files without an extension (after ".mustache" is removed).
`generatedFiles` renames this file to "LICENSE".

There were a few other approaches that we could use:
1. `WalkTemplatesDir` could use a different naming convention for elided
files (e.g. "internal_<name>.mustache")
2. `generatedFiles` could walk the template directory itself.

Author: brianquinlan

internal/sidekick/internal/dart/generate.go

@@ -62,12 +62,19 @@ func generatedFiles(model *api.API) []language.GeneratedFile {
 
 	files := language.WalkTemplatesDir(dartTemplates, "templates")
 
-	// Look for and replace 'main.dart' with '{servicename}.dart'
 	for index, fileInfo := range files {
+		// Replace 'main.dart' with '{servicename}.dart'
 		if filepath.Base(fileInfo.TemplatePath) == "main.dart.mustache" {
 			outDir := filepath.Dir(fileInfo.OutputPath)
 			fileInfo.OutputPath = filepath.Join(outDir, mainFileName+".dart")
 
+			files[index] = fileInfo
+		}
+		// Remove the extension from "LICENSE.txt".
+		if filepath.Base(fileInfo.OutputPath) == "LICENSE.txt" {
+			outDir := filepath.Dir(fileInfo.OutputPath)
+			fileInfo.OutputPath = filepath.Join(outDir, "LICENSE")
+
 			files[index] = fileInfo
 		}
 	}

internal/sidekick/internal/dart/generate_test.go

@@ -87,6 +87,9 @@ func TestGeneratedFiles(t *testing.T) {
 		if filepath.Base(fileInfo.OutputPath) == "main.dart" {
 			t.Errorf("expected the main.dart template to be generated as {servicename}.dart")
 		}
+		if filepath.Base(fileInfo.OutputPath) == "LICENSE.txt" {
+			t.Errorf("expected the LICENSE.txt template to be generated as LICENSE")
+		}
 	}
 }
 

internal/sidekick/internal/dart/templates/LICENSE.txt.mustache

@@ -0,0 +1,216 @@
+{{!
+Copyright 2025 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+}}
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internal/sidekick/internal/language/walk_templates_dir.go

@@ -32,6 +32,9 @@ import (
 //
 // Even in Rust, we may want to skip some files if the crate does not have
 // any services.
+//
+// Files whose output names would do not have an extension (e.g. `enum.mustache`) are
+// assumed to be used internally and are skipped.
 func WalkTemplatesDir(fsys fs.FS, root string) []GeneratedFile {
 	var result []GeneratedFile
 	fs.WalkDir(fsys, root, func(path string, d fs.DirEntry, err error) error {