WIP: Ensure that repository names don't start with ~

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

@@ -366,8 +366,16 @@ static BazelModuleResolutionValue createValue(
     // Calculate a unique name for each used extension id.
     BiMap<String, ModuleExtensionId> extensionUniqueNames = HashBiMap.create();
     for (ModuleExtensionId id : extensionUsagesById.rowKeySet()) {
-      String bestName =
-          id.getBzlFileLabel().getRepository().getName() + "~" + id.getExtensionName();
+      // Ensure that the resulting extension name (and thus the repository names derived from it) do
+      // not start with a tilde.
+      String repoName = id.getBzlFileLabel().getRepository().getName();
+      String nonEmptyRepoPart;
+      if (repoName.isEmpty()) {
+        nonEmptyRepoPart = "_main";
+      } else {
+        nonEmptyRepoPart = repoName;
+      }
+      String bestName = nonEmptyRepoPart + "~" + id.getExtensionName();
       if (extensionUniqueNames.putIfAbsent(bestName, id) == null) {
         continue;
       }

src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java

@@ -39,7 +39,10 @@ public final class RepositoryName {
 
   @SerializationConstant public static final RepositoryName MAIN = new RepositoryName("");
 
-  private static final Pattern VALID_REPO_NAME = Pattern.compile("[\\w\\-.~]*");
+  // Repository names must not start with a tilde as shells treat unescaped paths starting with them
+  // specially.
+  // https://www.gnu.org/software/bash/manual/html_node/Tilde-Expansion.html
+  private static final Pattern VALID_REPO_NAME = Pattern.compile("|[\\w\\-.][\\w\\-.~]*");
 
   // Must start with a letter. Can contain ASCII letters and digits, underscore, dash, and dot.
   private static final Pattern VALID_USER_PROVIDED_NAME = Pattern.compile("[a-zA-Z][-.\\w]*$");
@@ -156,7 +159,7 @@ static void validate(String name) throws LabelSyntaxException {
     if (!VALID_REPO_NAME.matcher(name).matches()) {
       throw LabelParser.syntaxErrorf(
           "invalid repository name '@%s': repo names may contain only A-Z, a-z, 0-9, '-', '_', '.'"
-              + " and '~'",
+              + " and '~' and must not start with '~'",
           StringUtilities.sanitizeControlChars(name));
     }
   }

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

@@ -1041,7 +1041,7 @@ public void generatedReposHaveCorrectMappings_strictDepsViolation() throws Excep
     assertThat(result.hasError()).isTrue();
     assertThat(result.getError().getException())
         .hasMessageThat()
-        .contains("No repository visible as '@foo' from repository '@~ext~ext'");
+        .contains("No repository visible as '@foo' from repository '@_main~ext~ext'");
   }
 
   @Test
@@ -1082,7 +1082,7 @@ public void importNonExistentRepo() throws Exception {
     scratch.file(workspaceRoot.getRelative("BUILD").getPathString());
     scratch.file(
         workspaceRoot.getRelative("data.bzl").getPathString(),
-        "load('@@~ext~ext//:data.bzl', ext_data='data')",
+        "load('@@_main~ext~ext//:data.bzl', ext_data='data')",
         "data=ext_data");
 
     SkyKey skyKey = BzlLoadValue.keyForBuild(Label.parseCanonical("//:data.bzl"));
@@ -1216,7 +1216,7 @@ public void extensionRepoCtxReadsFromAnotherExtensionRepo() throws Exception {
         workspaceRoot.getRelative("defs.bzl").getPathString(),
         "load('@data_repo//:defs.bzl','data_repo')",
         "def _ext_impl(ctx):",
-        "  data_file = ctx.read(Label('@@~my_ext2~candy2//:data.bzl'))",
+        "  data_file = ctx.read(Label('@@_main~my_ext2~candy2//:data.bzl'))",
         "  data_repo(name='candy1',data=data_file)",
         "my_ext=module_extension(implementation=_ext_impl)",
         "def _ext_impl2(ctx):",
@@ -1264,7 +1264,7 @@ public void testReportRepoAndBzlCycles_circularExtReposCtxRead() throws Exceptio
     SkyKey skyKey =
         PackageValue.key(
             PackageIdentifier.create(
-                RepositoryName.createUnvalidated("~my_ext~candy1"), PathFragment.EMPTY_FRAGMENT));
+                RepositoryName.createUnvalidated("_main~my_ext~candy1"), PathFragment.EMPTY_FRAGMENT));
     EvaluationResult<PackageValue> result =
         evaluator.evaluate(ImmutableList.of(skyKey), evaluationContext);
     assertThat(result.hasError()).isTrue();
@@ -1275,11 +1275,11 @@ public void testReportRepoAndBzlCycles_circularExtReposCtxRead() throws Exceptio
     assertContainsEvent(
         "ERROR <no location>: Circular definition of repositories generated by module extensions"
             + " and/or .bzl files:\n"
-            + ".-> @~my_ext~candy1\n"
+            + ".-> @_main~my_ext~candy1\n"
             + "|   extension 'my_ext' defined in //:defs.bzl\n"
-            + "|   @~my_ext2~candy2\n"
+            + "|   @_main~my_ext2~candy2\n"
             + "|   extension 'my_ext2' defined in //:defs.bzl\n"
-            + "`-- @~my_ext~candy1");
+            + "`-- @_main~my_ext~candy1");
   }
 
   @Test
@@ -1310,7 +1310,7 @@ public void testReportRepoAndBzlCycles_circularExtReposLoadInDefFile() throws Ex
     SkyKey skyKey =
         PackageValue.key(
             PackageIdentifier.create(
-                RepositoryName.createUnvalidated("~my_ext~candy1"),
+                RepositoryName.createUnvalidated("_main~my_ext~candy1"),
                 PathFragment.create("data.bzl")));
     EvaluationResult<PackageValue> result =
         evaluator.evaluate(ImmutableList.of(skyKey), evaluationContext);
@@ -1322,13 +1322,13 @@ public void testReportRepoAndBzlCycles_circularExtReposLoadInDefFile() throws Ex
     assertContainsEvent(
         "ERROR <no location>: Circular definition of repositories generated by module extensions"
             + " and/or .bzl files:\n"
-            + ".-> @~my_ext~candy1\n"
+            + ".-> @_main~my_ext~candy1\n"
             + "|   extension 'my_ext' defined in //:defs.bzl\n"
-            + "|   @~my_ext2~candy2\n"
+            + "|   @_main~my_ext2~candy2\n"
             + "|   extension 'my_ext2' defined in //:defs2.bzl\n"
             + "|   //:defs2.bzl\n"
-            + "|   @~my_ext~candy1//:data.bzl\n"
-            + "`-- @~my_ext~candy1");
+            + "|   @_main~my_ext~candy1//:data.bzl\n"
+            + "`-- @_main~my_ext~candy1");
   }
 
   @Test
@@ -1350,7 +1350,7 @@ public void testReportRepoAndBzlCycles_extRepoLoadSelfCycle() throws Exception {
     SkyKey skyKey =
         PackageValue.key(
             PackageIdentifier.create(
-                RepositoryName.createUnvalidated("~my_ext~candy1"),
+                RepositoryName.createUnvalidated("_main~my_ext~candy1"),
                 PathFragment.create("data.bzl")));
     EvaluationResult<PackageValue> result =
         evaluator.evaluate(ImmutableList.of(skyKey), evaluationContext);
@@ -1362,10 +1362,10 @@ public void testReportRepoAndBzlCycles_extRepoLoadSelfCycle() throws Exception {
     assertContainsEvent(
         "ERROR <no location>: Circular definition of repositories generated by module extensions"
             + " and/or .bzl files:\n"
-            + ".-> @~my_ext~candy1\n"
+            + ".-> @_main~my_ext~candy1\n"
             + "|   extension 'my_ext' defined in //:defs.bzl\n"
             + "|   //:defs.bzl\n"
-            + "|   @~my_ext~candy1//:data.bzl\n"
-            + "`-- @~my_ext~candy1");
+            + "|   @_main~my_ext~candy1//:data.bzl\n"
+            + "`-- @_main~my_ext~candy1");
   }
 }