Add ability to disable automatically loading config

Some applications might not want to automatically load a
detected smithy-build.json file. For example, if you're validating
that a JAR built from a package correctly defines all of its
dependencies correctly, then loading "sources" alongiside this
JAR can lead to conflicts. --no-config can be passed to disable
automatically loading a detected smithy-build.json file. Passing
this option and a -c parameter will fail validation.

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

@@ -79,4 +79,25 @@ public void successfullyDeDupesConfigAndCliArguments() {
             assertThat(result.getExitCode(), equalTo(0));
         });
     }
+
+    @Test
+    public void canDisableConfigFileDetection() {
+        // Disable the config file detection and don't pass model via positional arguments.
+        // This causes main.smithy to not be loaded.
+        IntegUtils.run("simple-config-sources", ListUtils.of("build", "--no-config"), result -> {
+            assertThat(result.getExitCode(), equalTo(0));
+            assertThat(result.hasArtifact("source", "sources", "main.smithy"), is(false));
+        });
+    }
+
+    @Test
+    public void failsWhenConfigIsProvidedAndDisabled() {
+        // Disable the config file detection and don't pass model via positional arguments.
+        // This causes main.smithy to not be loaded.
+        IntegUtils.run("simple-config-sources", ListUtils.of("build", "--no-config", "-c", "smithy-build.json"),
+                       result -> {
+            assertThat(result.getExitCode(), equalTo(1));
+            assertThat(result.getOutput(), containsString("Invalid combination of --no-config and --config"));
+        });
+    }
 }

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

@@ -27,18 +27,21 @@
 import software.amazon.smithy.build.SmithyBuild;
 import software.amazon.smithy.build.model.SmithyBuildConfig;
 import software.amazon.smithy.cli.ArgumentReceiver;
+import software.amazon.smithy.cli.CliError;
 import software.amazon.smithy.cli.HelpPrinter;
 
 final class ConfigOptions implements ArgumentReceiver {
 
     private static final Logger LOGGER = Logger.getLogger(ConfigOptions.class.getName());
     private final List<String> config = new ArrayList<>();
+    private boolean noConfig = false;
 
     @Override
     public void registerHelp(HelpPrinter printer) {
         printer.param("--config", "-c", "CONFIG_PATH...",
-                      "Path to smithy-build.json configuration (defaults to './smithy-build.json'). "
-                      + "This option can be repeated and each configured will be merged.");
+                      "Path to smithy-build.json config (defaults to ./smithy-build.json if not specified). "
+                      + "This option can be repeated, merging each config file.");
+        printer.option("--no-config", null, "Disable config file detection and use.");
     }
 
     @Override
@@ -52,9 +55,21 @@ public Consumer<String> testParameter(String name) {
         }
     }
 
+    @Override
+    public boolean testOption(String name) {
+        if (name.equals("--no-config")) {
+            noConfig = true;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
     List<String> config() {
         List<String> config = this.config;
-        if (config.isEmpty()) {
+
+        // Don't find the default config if --no-config is passed.
+        if (config.isEmpty() && !noConfig) {
             Path defaultConfig = Paths.get("smithy-build.json").toAbsolutePath();
             if (Files.exists(defaultConfig)) {
                 LOGGER.fine("Detected smithy-build.json at " + defaultConfig);
@@ -69,6 +84,11 @@ SmithyBuildConfig createSmithyBuildConfig() {
         SmithyBuildConfig smithyBuildConfig;
         List<String> config = config();
 
+        if (noConfig && !config.isEmpty()) {
+            throw new CliError("Invalid combination of --no-config and --config. --no-config can be omitted because "
+                               + "providing --config/-c disables automatically loading ./smithy-build.json.");
+        }
+
         if (config.isEmpty()) {
             smithyBuildConfig = SmithyBuildConfig.builder().version(SmithyBuild.VERSION).build();
         } else {