Check for existing directory when creating template with init (smithy-lang#1885)

This commit updates the Smithy Init CLI command to fail before attempting to clone the template folder when the target 
output directory already exists.

---------
Co-authored-by: Michael Dowling <[email protected]>

Author: hpmellema

smithy-cli/src/it/java/software/amazon/smithy/cli/InitCommandTest.java

@@ -208,6 +208,30 @@ public void withListArg() {
         });
     }
 
+    @Test
+    public void outputDirectoryAlreadyExists() {
+        IntegUtils.withProject(PROJECT_NAME, templatesDir -> {
+            setupTemplatesDirectory(templatesDir);
+
+            IntegUtils.withTempDir("existingOutputDir", dir -> {
+                Path existingPath = null;
+                RunResult result;
+                try {
+                    existingPath = Files.createDirectory(dir.resolve("quickstart-cli"));
+                    result = IntegUtils.run(
+                            dir, ListUtils.of("init", "-t", "quickstart-cli", "-u", templatesDir.toString()));
+                } catch (IOException e) {
+                    throw new RuntimeException(e);
+                } finally {
+                    IoUtils.rmdir(existingPath);
+                }
+
+                assertThat(result.getOutput(), containsString("Output directory `quickstart-cli` already exists."));
+                assertThat(result.getExitCode(), is(1));
+            });
+        });
+    }
+
     private static void run(List<String> args, Path root) {
         StringBuilder output = new StringBuilder();
         int result = IoUtils.runCommand(args, root, output, Collections.emptyMap());

smithy-cli/src/main/java/software/amazon/smithy/cli/commands/InitCommand.java

@@ -160,6 +160,15 @@ private void cloneTemplate(Path temp, ObjectNode smithyTemplatesNode, String tem
             throw new IllegalArgumentException("Please specify a template name using `--template` or `-t`");
         }
 
+        // Use templateName if directory is not specified
+        if (directory == null) {
+            directory = template;
+        }
+        final Path dest = Paths.get(directory);
+        if (Files.exists(dest)) {
+            throw new CliError("Output directory `" + directory + "` already exists.");
+        }
+
         ObjectNode templatesNode = getTemplatesNode(smithyTemplatesNode);
         if (!templatesNode.containsMember(template)) {
             throw new IllegalArgumentException(String.format(
@@ -180,12 +189,8 @@ private void cloneTemplate(Path temp, ObjectNode smithyTemplatesNode, String tem
         }
         exec(ListUtils.of("git", "checkout"), temp);
 
-        // Use templateName if directory is not specified
-        if (directory == null) {
-            directory = template;
-        }
 
-        final Path dest = Paths.get(directory);
+
         IoUtils.copyDir(Paths.get(temp.toString(), templatePath), dest);
         copyIncludedFiles(temp.toString(), dest.toString(), includedFiles, template, env);