[clang] [clang][Sema] Fix initialization of `NonTypeTemplateParmDecl`... (PR #121768)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-modules

@llvm/pr-subscribers-clang

Author: Alejandro Álvarez Ayllón (alejandro-alvarez-sonarsource)

<details>
<summary>Changes</summary>

...when there are invalid constraints.

When attaching a `TypeConstraint`, in case of error, the trailing pointer that is supposed to point to the constraint is left uninitialized.
Sometimes the uninitialized value will be a `nullptr`, but at other times it will not. If we traverse the AST (for instance, dumping it, or when writing the BMI), we may get a crash depending on the value that was left. The serialization may also contain a bogus value.

With this commit, we always initialize this trailing pointer, using a `RecoveryExpr` in case of failure to parse.

This does not affect only modules, but it causes a segfault more consistently when they are involved.

The test case was reduced from mp-units.

---
Full diff: https://github.com/llvm/llvm-project/pull/121768.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaTemplate.cpp (+16-2) 
- (added) clang/test/Modules/malformed-constraint-template-non-type-parm-decl.cpp (+54) 


``````````diff
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 20ec2fbeaa6a8b..9b51f973fb2bb8 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1235,6 +1235,10 @@ bool Sema::AttachTypeConstraint(AutoTypeLoc TL,
         << NewConstrainedParm->getTypeSourceInfo()
                ->getTypeLoc()
                .getSourceRange();
+    NewConstrainedParm->setPlaceholderTypeConstraint(
+        RecoveryExpr::Create(Context, OrigConstrainedParm->getType(),
+                             OrigConstrainedParm->getBeginLoc(),
+                             OrigConstrainedParm->getEndLoc(), {}));
     return true;
   }
   // FIXME: Concepts: This should be the type of the placeholder, but this is
@@ -1242,8 +1246,13 @@ bool Sema::AttachTypeConstraint(AutoTypeLoc TL,
   DeclRefExpr *Ref =
       BuildDeclRefExpr(OrigConstrainedParm, OrigConstrainedParm->getType(),
                        VK_PRValue, OrigConstrainedParm->getLocation());
-  if (!Ref)
+  if (!Ref) {
+    NewConstrainedParm->setPlaceholderTypeConstraint(
+        RecoveryExpr::Create(Context, OrigConstrainedParm->getType(),
+                             OrigConstrainedParm->getBeginLoc(),
+                             OrigConstrainedParm->getEndLoc(), {}));
     return true;
+  }
   ExprResult ImmediatelyDeclaredConstraint = formImmediatelyDeclaredConstraint(
       *this, TL.getNestedNameSpecifierLoc(), TL.getConceptNameInfo(),
       TL.getNamedConcept(), /*FoundDecl=*/TL.getFoundDecl(), TL.getLAngleLoc(),
@@ -1255,8 +1264,13 @@ bool Sema::AttachTypeConstraint(AutoTypeLoc TL,
       },
       EllipsisLoc);
   if (ImmediatelyDeclaredConstraint.isInvalid() ||
-      !ImmediatelyDeclaredConstraint.isUsable())
+      !ImmediatelyDeclaredConstraint.isUsable()) {
+    NewConstrainedParm->setPlaceholderTypeConstraint(
+        RecoveryExpr::Create(Context, OrigConstrainedParm->getType(),
+                             OrigConstrainedParm->getBeginLoc(),
+                             OrigConstrainedParm->getEndLoc(), {}));
     return true;
+  }
 
   NewConstrainedParm->setPlaceholderTypeConstraint(
       ImmediatelyDeclaredConstraint.get());
diff --git a/clang/test/Modules/malformed-constraint-template-non-type-parm-decl.cpp b/clang/test/Modules/malformed-constraint-template-non-type-parm-decl.cpp
new file mode 100644
index 00000000000000..cea6404bbebd28
--- /dev/null
+++ b/clang/test/Modules/malformed-constraint-template-non-type-parm-decl.cpp
@@ -0,0 +1,54 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -std=c++20 mod.cppm -emit-module-interface -o mod.pcm -fallow-pcm-with-compiler-errors -verify
+// RUN: %clang_cc1 -std=c++20 main.cpp -fmodule-file=mod=mod.pcm -verify -fallow-pcm-with-compiler-errors -fsyntax-only -ast-dump-all | FileCheck %s
+
+//--- mod.cppm
+export module mod;
+
+template <typename T, auto Q>
+concept ReferenceOf = Q;
+
+// expected-error at +2 {{unknown type name 'AngleIsInvalidNow'}}
+// expected-error at +1 {{constexpr variable 'angle' must be initialized by a constant expression}}
+constexpr struct angle {AngleIsInvalidNow e;} angle;
+
+// expected-error at +1 {{non-type template argument is not a constant expression}}
+template<ReferenceOf<angle> auto R, typename Rep> requires requires(Rep v) {cos(v);}
+auto cos(const Rep& q);
+
+// expected-error at +1 {{non-type template argument is not a constant expression}}
+template<ReferenceOf<angle> auto R, typename Rep> requires requires(Rep v) {tan(v);}
+auto tan(const Rep& q);
+
+//--- main.cpp
+// expected-no-diagnostics
+import mod;
+
+// CHECK:      |-FunctionTemplateDecl {{.*}} <line:11:1, line:12:22> col:6 imported in mod hidden invalid cos
+// CHECK-NEXT: | |-NonTypeTemplateParmDecl {{.*}} <line:11:10, col:34> col:34 imported in mod hidden referenced invalid 'ReferenceOf<angle> auto' depth 0 index 0 R
+// CHECK-NEXT: | | `-RecoveryExpr {{.*}} <col:10, col:34> 'ReferenceOf<angle> auto' contains-errors lvalue
+// CHECK-NEXT: | |-TemplateTypeParmDecl {{.*}} <col:37, col:46> col:46 imported in mod hidden referenced typename depth 0 index 1 Rep
+// CHECK-NEXT: | |-RequiresExpr {{.*}} <col:60, col:84> 'bool'
+// CHECK-NEXT: | | |-ParmVarDecl {{.*}} <col:69, col:73> col:73 imported in mod hidden referenced v 'Rep'
+// CHECK-NEXT: | | `-SimpleRequirement {{.*}} dependent
+// CHECK-NEXT: | |   `-CallExpr {{.*}} <col:77, col:82> '<dependent type>'
+// CHECK-NEXT: | |     |-UnresolvedLookupExpr {{.*}} <col:77> '<overloaded function type>' lvalue (ADL) = 'cos' empty
+// CHECK-NEXT: | |     `-DeclRefExpr {{.*}} <col:81> 'Rep' lvalue ParmVar {{.*}} 'v' 'Rep' non_odr_use_unevaluated
+// CHECK-NEXT: | `-FunctionDecl {{.*}} <line:12:1, col:22> col:6 imported in mod hidden cos 'auto (const Rep &)'
+// CHECK-NEXT: |   `-ParmVarDecl {{.*}} <col:10, col:21> col:21 imported in mod hidden q 'const Rep &'
+
+// CHECK:      |-FunctionTemplateDecl {{.*}} <line:15:1, line:16:22> col:6 imported in mod hidden invalid tan
+// CHECK-NEXT: | |-NonTypeTemplateParmDecl {{.*}} <line:15:10, col:34> col:34 imported in mod hidden referenced invalid 'ReferenceOf<angle> auto' depth 0 index 0 R
+// CHECK-NEXT: | | `-RecoveryExpr {{.*}} <col:10, col:34> 'ReferenceOf<angle> auto' contains-errors lvalue
+// CHECK-NEXT: | |-TemplateTypeParmDecl {{.*}} <col:37, col:46> col:46 imported in mod hidden referenced typename depth 0 index 1 Rep
+// CHECK-NEXT: | |-RequiresExpr {{.*}} <col:60, col:84> 'bool'
+// CHECK-NEXT: | | |-ParmVarDecl {{.*}} <col:69, col:73> col:73 imported in mod hidden referenced v 'Rep'
+// CHECK-NEXT: | | `-SimpleRequirement {{.*}} dependent
+// CHECK-NEXT: | |   `-CallExpr {{.*}} <col:77, col:82> '<dependent type>'
+// CHECK-NEXT: | |     |-UnresolvedLookupExpr {{.*}} <col:77> '<overloaded function type>' lvalue (ADL) = 'tan' empty
+// CHECK-NEXT: | |     `-DeclRefExpr {{.*}} <col:81> 'Rep' lvalue ParmVar {{.*}} 'v' 'Rep' non_odr_use_unevaluated
+// CHECK-NEXT: | `-FunctionDecl {{.*}} <line:16:1, col:22> col:6 imported in mod hidden tan 'auto (const Rep &)'
+// CHECK-NEXT: |   `-ParmVarDecl {{.*}} <col:10, col:21> col:21 imported in mod hidden q 'const Rep &'

``````````

</details>


https://github.com/llvm/llvm-project/pull/121768