Allow one-character module names

Makes testing slightly easier.

PiperOrigin-RevId: 469962515
Change-Id: I67c6c5f5f732a80b0807d8580b4117f2d18c175e

src/main/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileGlobals.java

@@ -54,10 +54,9 @@
 public class ModuleFileGlobals {
   /**
    * A valid module name must: 1) begin with a lowercase letter; 2) end with a lowercase letter or a
-   * digit; 3) be at least 2 characters long; 4) contain only lowercase letters, digits, or one of
-   * '._-'.
+   * digit; 3) contain only lowercase letters, digits, or one of * '._-'.
    */
-  private static final Pattern VALID_MODULE_NAME = Pattern.compile("[a-z][a-z0-9._-]*[a-z0-9]");
+  private static final Pattern VALID_MODULE_NAME = Pattern.compile("[a-z]([a-z0-9._-]*[a-z0-9])?");
 
   private boolean moduleCalled = false;
   private final boolean ignoreDevDeps;
@@ -114,8 +113,7 @@ static void validateModuleName(String moduleName) throws EvalException {
       throw Starlark.errorf(
           "invalid module name '%s': valid names must 1) only contain lowercase letters (a-z),"
               + " digits (0-9), dots (.), hyphens (-), and underscores (_); 2) begin with a"
-              + " lowercase letter; 3) end with a lowercase letter or digit; 4) be at least two"
-              + " characters long.",
+              + " lowercase letter; 3) end with a lowercase letter or digit.",
           moduleName);
     }
   }
@@ -136,7 +134,7 @@ static void validateModuleName(String moduleName) throws EvalException {
                     + " in, if it's not going to be depended on by another module). A valid module"
                     + " name must: 1) only contain lowercase letters (a-z), digits (0-9), dots (.),"
                     + " hyphens (-), and underscores (_); 2) begin with a lowercase letter; 3) end"
-                    + " with a lowercase letter or digit; 4) be at least two characters long.",
+                    + " with a lowercase letter or digit.",
             named = true,
             positional = false,
             defaultValue = "''"),

src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileFunctionTest.java

@@ -642,9 +642,9 @@ public void validateModuleName() throws Exception {
     ModuleFileGlobals.validateModuleName("a3");
     ModuleFileGlobals.validateModuleName("a.e");
     ModuleFileGlobals.validateModuleName("a.-_e");
+    ModuleFileGlobals.validateModuleName("a");
 
     assertThrows(EvalException.class, () -> ModuleFileGlobals.validateModuleName(""));
-    assertThrows(EvalException.class, () -> ModuleFileGlobals.validateModuleName("f"));
     assertThrows(EvalException.class, () -> ModuleFileGlobals.validateModuleName("fooBar"));
     assertThrows(EvalException.class, () -> ModuleFileGlobals.validateModuleName("_foo"));
     assertThrows(EvalException.class, () -> ModuleFileGlobals.validateModuleName("foo#bar"));
@@ -655,24 +655,24 @@ public void validateModuleName() throws Exception {
   public void badModuleName_module() throws Exception {
     scratch.file(
         rootDirectory.getRelative("MODULE.bazel").getPathString(),
-        "module(name='f',version='0.1')");
+        "module(name='f.',version='0.1')");
 
     reporter.removeHandler(failFastHandler); // expect failures
     evaluator.evaluate(ImmutableList.of(ModuleFileValue.KEY_FOR_ROOT_MODULE), evaluationContext);
 
-    assertContainsEvent("invalid module name 'f'");
+    assertContainsEvent("invalid module name 'f.'");
   }
 
   @Test
   public void badModuleName_bazelDep() throws Exception {
     scratch.file(
         rootDirectory.getRelative("MODULE.bazel").getPathString(),
-        "bazel_dep(name='f',version='0.1')");
+        "bazel_dep(name='f.',version='0.1')");
 
     reporter.removeHandler(failFastHandler); // expect failures
     evaluator.evaluate(ImmutableList.of(ModuleFileValue.KEY_FOR_ROOT_MODULE), evaluationContext);
 
-    assertContainsEvent("invalid module name 'f'");
+    assertContainsEvent("invalid module name 'f.'");
   }
 
   @Test