[Clang] fix crash due to incorrect argument position in merging deduced template arguments

[a-tarasyuk]

Fixes #113659

[llvmbot]

@llvm/pr-subscribers-clang

Author: Oleksandr T. (a-tarasyuk)

Changes

Fixes #113659

---

Full diff: https://github.com/llvm/llvm-project/pull/118041.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/Sema/SemaTemplateDeduction.cpp (+2-1)
• (added) clang/test/SemaTemplate/template-args-deduction-aggregates.cpp (+12)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2ecd19bdc39448..7e78e7eb9ec0a3 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -760,6 +760,7 @@ Bug Fixes to C++ Support
   missing placeholder return type. (#GH78694)
 - Fixed a bug where bounds of partially expanded pack indexing expressions were checked too early. (#GH116105)
 - Fixed an assertion failure caused by using ``consteval`` in condition in consumed analyses. (#GH117385)
+- Fix a crash caused by incorrect argument position in merging deduced template arguments. (#GH113659)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 62a0c30d995020..fad20b37a7d9a2 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/clang/lib/Sema/SemaTemplateDeduction.cpp
@@ -376,7 +376,7 @@ checkDeducedTemplateArguments(ASTContext &Context,
     for (TemplateArgument::pack_iterator
              XA = X.pack_begin(),
              XAEnd = X.pack_end(), YA = Y.pack_begin(), YAEnd = Y.pack_end();
-         XA != XAEnd; ++XA, ++YA) {
+         XA != XAEnd; ++XA) {
       if (YA != YAEnd) {
         TemplateArgument Merged = checkDeducedTemplateArguments(
             Context, DeducedTemplateArgument(*XA, X.wasDeducedFromArrayBound()),
@@ -384,6 +384,7 @@ checkDeducedTemplateArguments(ASTContext &Context,
         if (Merged.isNull() && !(XA->isNull() && YA->isNull()))
           return DeducedTemplateArgument();
         NewPack.push_back(Merged);
+        ++YA;
       } else {
         NewPack.push_back(*XA);
       }
diff --git a/clang/test/SemaTemplate/template-args-deduction-aggregates.cpp b/clang/test/SemaTemplate/template-args-deduction-aggregates.cpp
new file mode 100644
index 00000000000000..afe78d0873bb33
--- /dev/null
+++ b/clang/test/SemaTemplate/template-args-deduction-aggregates.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++20
+
+// expected-no-diagnostics
+
+namespace GH113659 {
+template <class... Args> struct S {};
+struct T {};
+struct U {};
+
+template <class... Args> struct B : S<Args...>, Args... {};
+B b{S<T, U>{}};
+}

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-aarch64-quick running on linaro-clang-aarch64-quick while building clang at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/8581

Here is the relevant piece of the build log for the reference

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'lit :: googletest-timeout.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 9
not env -u FILECHECK_OPTS "/usr/bin/python3.10" /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 --order=lexical -v Inputs/googletest-timeout    --param gtest_filter=InfiniteLoopSubTest --timeout=1 > /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/Output/googletest-timeout.py.tmp.cmd.out
# executed command: not env -u FILECHECK_OPTS /usr/bin/python3.10 /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit.py -j1 --order=lexical -v Inputs/googletest-timeout --param gtest_filter=InfiniteLoopSubTest --timeout=1
# .---command stderr------------
# | lit.py: /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/utils/lit/lit/main.py:72: note: The test suite configuration requested an individual test timeout of 0 seconds but a timeout of 1 seconds was requested on the command line. Forcing timeout to be 1 seconds.
# `-----------------------------
# RUN: at line 11
FileCheck --check-prefix=CHECK-INF < /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/Output/googletest-timeout.py.tmp.cmd.out /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/googletest-timeout.py
# executed command: FileCheck --check-prefix=CHECK-INF /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/googletest-timeout.py
# .---command stderr------------
# | /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/googletest-timeout.py:34:14: error: CHECK-INF: expected string not found in input
# | # CHECK-INF: Timed Out: 1
# |              ^
# | <stdin>:13:29: note: scanning from here
# | Reached timeout of 1 seconds
# |                             ^
# | <stdin>:37:2: note: possible intended match here
# |  Timed Out: 2 (100.00%)
# |  ^
# | 
# | Input file: <stdin>
# | Check file: /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/utils/lit/tests/googletest-timeout.py
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             .
# |             .
# |             .
# |             8:  
# |             9:  
# |            10: -- 
# |            11: exit: -9 
# |            12: -- 
# |            13: Reached timeout of 1 seconds 
# | check:34'0                                 X error: no match found
# |            14: ******************** 
# | check:34'0     ~~~~~~~~~~~~~~~~~~~~~
# |            15: TIMEOUT: googletest-timeout :: DummySubDir/OneTest.py/1/2 (2 of 2) 
# | check:34'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |            16: ******************** TEST 'googletest-timeout :: DummySubDir/OneTest.py/1/2' FAILED ******************** 
# | check:34'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |            17: Script(shard): 
# | check:34'0     ~~~~~~~~~~~~~~~
...