Backport: [clang] Serialization: support hashing null template arguments

[mizvekov]

When performing overload resolution during code completion, clang will allow incomplete substitutions in more places than would be allowed for valid code, because for completion to work well, it needs clang to keep going so it can explore the space of possibilities.

Notably, we accept instantiating declarations will null template arguments, and this works fine, except that when lazily loading serialized templated declarations, the template argument hasher assumes null arguments can't be used.

This patch makes the hasher happily accept that.

Fixes #139019

[llvmbot]

@llvm/pr-subscribers-clang

Author: Matheus Izvekov (mizvekov)

Changes

When performing overload resolution during code completion, clang will allow incomplete substitutions in more places than would be allowed for valid code, because for completion to work well, it needs clang to keep going so it can explore the space of possibilities.

Notably, we accept instantiating declarations will null template arguments, and this works fine, except that when lazily loading serialzied templated declarations, the template argument hasher assumes null arguments can't be used.

This patch makes the hasher happily accept that.

Fixes #139019

---

Full diff: https://github.com/llvm/llvm-project/pull/141957.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/Serialization/TemplateArgumentHasher.cpp (+3-1)
• (added) clang/test/CodeCompletion/GH139019.cpp (+26)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7b84210fddab3..262bf4e3d4f5b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1118,6 +1118,7 @@ Miscellaneous Clang Crashes Fixed
 
 - Fixed a crash when an unscoped enumeration declared by an opaque-enum-declaration within a class template
   with a dependent underlying type is subject to integral promotion. (#GH117960)
+- Fix code completion crash involving PCH serialzied templates. (#GH139019)
 
 OpenACC Specific Changes
 ------------------------
diff --git a/clang/lib/Serialization/TemplateArgumentHasher.cpp b/clang/lib/Serialization/TemplateArgumentHasher.cpp
index 598f098f526d0..5fd6941256fe2 100644
--- a/clang/lib/Serialization/TemplateArgumentHasher.cpp
+++ b/clang/lib/Serialization/TemplateArgumentHasher.cpp
@@ -65,7 +65,9 @@ void TemplateArgumentHasher::AddTemplateArgument(TemplateArgument TA) {
 
   switch (Kind) {
   case TemplateArgument::Null:
-    llvm_unreachable("Expected valid TemplateArgument");
+    // These can occur in incomplete substitutions performed with code
+    // completion (see PartialOverloading).
+    break;
   case TemplateArgument::Type:
     AddQualType(TA.getAsType());
     break;
diff --git a/clang/test/CodeCompletion/GH139019.cpp b/clang/test/CodeCompletion/GH139019.cpp
new file mode 100644
index 0000000000000..fed35b38362a1
--- /dev/null
+++ b/clang/test/CodeCompletion/GH139019.cpp
@@ -0,0 +1,26 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/test.hpp -emit-pch -o %t/1.pch
+// RUN: %clang_cc1 -std=c++20 %t/test.cpp -include-pch %t/1.pch -code-completion-at=%t/test.cpp:7:17
+
+//--- test.hpp
+#pragma once
+class provider_t
+{
+  public:
+    template<class T>
+    void emit(T *data)
+    {}
+};
+
+//--- test.cpp
+#include "test.hpp"
+
+void test()
+{
+    provider_t *focus;
+    void *data;
+    focus->emit(&data);
+}

[llvmbot]

@llvm/pr-subscribers-clang-modules

Author: Matheus Izvekov (mizvekov)

Changes

When performing overload resolution during code completion, clang will allow incomplete substitutions in more places than would be allowed for valid code, because for completion to work well, it needs clang to keep going so it can explore the space of possibilities.

Notably, we accept instantiating declarations will null template arguments, and this works fine, except that when lazily loading serialzied templated declarations, the template argument hasher assumes null arguments can't be used.

This patch makes the hasher happily accept that.

Fixes #139019

---

Full diff: https://github.com/llvm/llvm-project/pull/141957.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/Serialization/TemplateArgumentHasher.cpp (+3-1)
• (added) clang/test/CodeCompletion/GH139019.cpp (+26)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7b84210fddab3..262bf4e3d4f5b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1118,6 +1118,7 @@ Miscellaneous Clang Crashes Fixed
 
 - Fixed a crash when an unscoped enumeration declared by an opaque-enum-declaration within a class template
   with a dependent underlying type is subject to integral promotion. (#GH117960)
+- Fix code completion crash involving PCH serialzied templates. (#GH139019)
 
 OpenACC Specific Changes
 ------------------------
diff --git a/clang/lib/Serialization/TemplateArgumentHasher.cpp b/clang/lib/Serialization/TemplateArgumentHasher.cpp
index 598f098f526d0..5fd6941256fe2 100644
--- a/clang/lib/Serialization/TemplateArgumentHasher.cpp
+++ b/clang/lib/Serialization/TemplateArgumentHasher.cpp
@@ -65,7 +65,9 @@ void TemplateArgumentHasher::AddTemplateArgument(TemplateArgument TA) {
 
   switch (Kind) {
   case TemplateArgument::Null:
-    llvm_unreachable("Expected valid TemplateArgument");
+    // These can occur in incomplete substitutions performed with code
+    // completion (see PartialOverloading).
+    break;
   case TemplateArgument::Type:
     AddQualType(TA.getAsType());
     break;
diff --git a/clang/test/CodeCompletion/GH139019.cpp b/clang/test/CodeCompletion/GH139019.cpp
new file mode 100644
index 0000000000000..fed35b38362a1
--- /dev/null
+++ b/clang/test/CodeCompletion/GH139019.cpp
@@ -0,0 +1,26 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/test.hpp -emit-pch -o %t/1.pch
+// RUN: %clang_cc1 -std=c++20 %t/test.cpp -include-pch %t/1.pch -code-completion-at=%t/test.cpp:7:17
+
+//--- test.hpp
+#pragma once
+class provider_t
+{
+  public:
+    template<class T>
+    void emit(T *data)
+    {}
+};
+
+//--- test.cpp
+#include "test.hpp"
+
+void test()
+{
+    provider_t *focus;
+    void *data;
+    focus->emit(&data);
+}