From ea5a4c6c8fa2b62a9817090aa981f1c9a8b05920 Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Tue, 30 Jul 2024 10:28:32 -0700
Subject: [PATCH 1/2] Fix namespace in blockless namespace

---
 packages/compiler/src/core/binder.ts  |  3 ++-
 packages/compiler/src/core/parser.ts  |  2 +-
 packages/compiler/test/binder.test.ts | 38 +++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/packages/compiler/src/core/binder.ts b/packages/compiler/src/core/binder.ts
index 6f8b9087b53..eb5a1fc91f5 100644
--- a/packages/compiler/src/core/binder.ts
+++ b/packages/compiler/src/core/binder.ts
@@ -490,8 +490,9 @@ export function createBinder(program: Program): Binder {
   }
 
   function bindNamespaceStatement(statement: NamespaceStatementNode) {
+    const effectiveScope = fileNamespace ?? scope;
     // check if there's an existing symbol for this namespace
-    const existingBinding = (scope as NamespaceStatementNode).symbol.exports!.get(statement.id.sv);
+    const existingBinding = effectiveScope.symbol.exports!.get(statement.id.sv);
     if (existingBinding && existingBinding.flags & SymbolFlags.Namespace) {
       mutate(statement).symbol = existingBinding;
       // locals are never shared.
diff --git a/packages/compiler/src/core/parser.ts b/packages/compiler/src/core/parser.ts
index 29176357087..f9e834b03e4 100644
--- a/packages/compiler/src/core/parser.ts
+++ b/packages/compiler/src/core/parser.ts
@@ -582,7 +582,7 @@ function createParser(code: string | SourceFile, options: ParseOptions = {}): Pa
         case Token.NamespaceKeyword:
           const ns = parseNamespaceStatement(pos, decorators, docs, directives);
 
-          if (!Array.isArray(ns.statements)) {
+          if (isBlocklessNamespace(ns)) {
             error({ code: "blockless-namespace-first", messageId: "topLevel", target: ns });
           }
           item = ns;
diff --git a/packages/compiler/test/binder.test.ts b/packages/compiler/test/binder.test.ts
index afd59ede91f..1ff2fa6ffb7 100644
--- a/packages/compiler/test/binder.test.ts
+++ b/packages/compiler/test/binder.test.ts
@@ -60,6 +60,44 @@ describe("compiler: binder", () => {
       },
     });
   });
+
+  it("namespace inside blockless namespace with the same name", () => {
+    const code = `
+      namespace A.B;
+      namespace A.B {
+        model D { }
+      }
+    `;
+    const script = bindTypeSpec(code);
+    strictEqual(script.namespaces.length, 4);
+    assertBindings("root", script.symbol.exports!, {
+      A: {
+        declarations: [SyntaxKind.NamespaceStatement],
+        flags: SymbolFlags.Namespace,
+        exports: {
+          B: {
+            flags: SymbolFlags.Namespace,
+            exports: {
+              A: {
+                declarations: [SyntaxKind.NamespaceStatement],
+                flags: SymbolFlags.Namespace,
+                exports: {
+                  B: {
+                    flags: SymbolFlags.Namespace,
+                    exports: {
+                      D: {
+                        flags: SymbolFlags.Model,
+                      },
+                    },
+                  },
+                },
+              },
+            },
+          },
+        },
+      },
+    });
+  });
   it("binds namespaces", () => {
     const code = `
       namespace A {

From a1d8ce706530a38c5b872a92d421dacbf5907434 Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Tue, 30 Jul 2024 10:35:44 -0700
Subject: [PATCH 2/2] Add changelogs

---
 ...mespace-in-blockless-2024-6-30-10-29-59.md | 14 ++++++++
 ...mespace-in-blockless-2024-6-30-10-31-17.md | 33 +++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 .chronus/changes/fix-namespace-in-blockless-2024-6-30-10-29-59.md
 create mode 100644 .chronus/changes/fix-namespace-in-blockless-2024-6-30-10-31-17.md

diff --git a/.chronus/changes/fix-namespace-in-blockless-2024-6-30-10-29-59.md b/.chronus/changes/fix-namespace-in-blockless-2024-6-30-10-29-59.md
new file mode 100644
index 00000000000..74ecf7faa5b
--- /dev/null
+++ b/.chronus/changes/fix-namespace-in-blockless-2024-6-30-10-29-59.md
@@ -0,0 +1,14 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/compiler"
+---
+
+Allow using compact namespace form `Foo.Bar` when inside another namespace
+  ```tsp
+  namespace MyOrg.MyProject {
+    namespace MyModule.MySubmodule { // <-- this used to emit an error
+      // ...
+    }
+  }
+  ```
diff --git a/.chronus/changes/fix-namespace-in-blockless-2024-6-30-10-31-17.md b/.chronus/changes/fix-namespace-in-blockless-2024-6-30-10-31-17.md
new file mode 100644
index 00000000000..11ee6c6cb9d
--- /dev/null
+++ b/.chronus/changes/fix-namespace-in-blockless-2024-6-30-10-31-17.md
@@ -0,0 +1,33 @@
+---
+changeKind: breaking
+packages:
+  - "@typespec/compiler"
+---
+
+Fix issue where naming a namespace with the same name as the blockless namespace would merge with it instead of creating a subnamespace like any other name would.
+
+  ```tsp
+  namespace MyOrg.MyProject;
+
+  namespace MyOrg.MyProject.MyArea {
+    model A {}
+  }
+
+  namespace MyArea2 {
+    model B {}
+  }
+  ```
+
+  Previously model `A` would end-up in namespace `MyOrg.MyProject.MyArea` and model `B` in `MyOrg.MyProject.MyArea2`. With this change model `A` will now be in `MyOrg.MyProject.MyOrg.MyProject.MyArea`. To achieve the previous behavior the above code should be written as:
+
+  ```tsp
+  namespace MyOrg.MyProject;
+
+  namespace MyArea {
+    model A {}
+  }
+
+  namespace MyArea2 {
+    model B {}
+  }
+  ```