[C++20][Modules] Fix crash when function and lambda inside loaded from different modules (#109167)

Summary:
Because AST loading code is lazy and happens in unpredictable order, it
is possible that

[C++20][Modules] Fix crash when function and lambda inside loaded from different modules (#109167)

Summary:
Because AST loading code is lazy and happens in unpredictable order, it
is possible that a function and lambda inside the function can be loaded
from different modules. As a result, the captured DeclRefExpr won’t
match the corresponding VarDecl inside the function. This situation is
reflected in the AST as follows:

```
FunctionDecl 0x555564f4aff0 <Conv.h:33:1, line:41:1> line:33:35 imported in ./thrift_cpp2_base.h hidden tryTo 'Expected<Tgt, const char *> ()' inline
|-also in ./folly-conv.h
`-CompoundStmt 0x555564f7cfc8 <col:43, line:41:1>
|-DeclStmt 0x555564f7ced8 <line:34:3, col:17>
| `-VarDecl 0x555564f7cef8 <col:3, col:16> col:7 imported in ./thrift_cpp2_base.h hidden referenced result 'Tgt' cinit
| `-IntegerLiteral 0x555564f7d080 <col:16> 'int' 0
|-CallExpr 0x555564f7cea8 <line:39:3, col:76> '<dependent type>'
| |-UnresolvedLookupExpr 0x555564f7bea0 <col:3, col:19> '<overloaded function type>' lvalue (no ADL) = 'then_' 0x555564f7bef0
| |-CXXTemporaryObjectExpr 0x555564f7bcb0 <col:25, col:45> 'Expected<bool, int>':'folly::Expected<bool, int>' 'void () noexcept' zeroing
| `-LambdaExpr 0x555564f7bc88 <col:48, col:75> '(lambda at Conv.h:39:48)'
| |-CXXRecordDecl 0x555564f76b88 <col:48> col:48 imported in ./folly-conv.h hidden implicit <undeserialized declarations> class definition
| | |-also in ./thrift_cpp2_base.h
| | `-DefinitionData lambda empty standard_layout trivially_copyable literal can_const_default_init
| | |-DefaultConstructor defaulted_is_constexpr
| | |-CopyConstructor simple trivial has_const_param needs_implicit implicit_has_const_param
| | |-MoveConstructor exists simple trivial needs_implicit
| | |-CopyAssignment trivial has_const_param needs_implicit implicit_has_const_param
| | |-MoveAssignment
| | `-Destructor simple irrelevant trivial constexpr needs_implicit
| `-CompoundStmt 0x555564f7d1a8 <col:58, col:75>
| `-ReturnStmt 0x555564f7d198 <col:60, col:67>
| `-DeclRefExpr 0x555564f7d0a0 <col:67> 'Tgt' lvalue Var 0x555564f7d0c8 'result' 'Tgt' refers_to_enclosing_variable_or_capture
`-ReturnStmt 0x555564f7bc78 <line:40:3, col:11>
`-InitListExpr 0x555564f7bc38 <col:10, col:11> 'void'
```

This diff modifies the AST deserialization process to load lambdas
within the canonical function declaration sooner, immediately following
the function, ensuring that they are loaded from the same module.

Re-land https://github.com/llvm/llvm-project/pull/104512 Added test case
that caused crash due to multiple enclosed lambdas deserialization.

Test Plan: check-clang

show more ...

[RFC][C++20][Modules] Fix crash when function and lambda inside loaded from different modules (#104512)

Summary:
Because AST loading code is lazy and happens in unpredictable order it
could happen

[RFC][C++20][Modules] Fix crash when function and lambda inside loaded from different modules (#104512)

Summary:
Because AST loading code is lazy and happens in unpredictable order it
could happen that function and lambda inside function can be loaded from
different modules. In this case, captured DeclRefExpr won’t match the
corresponding VarDecl inside function. In AST it looks like this:
```
FunctionDecl 0x555564f4aff0 <Conv.h:33:1, line:41:1> line:33:35 imported in ./thrift_cpp2_base.h hidden tryTo 'Expected<Tgt, const char *> ()' inline
|-also in ./folly-conv.h
`-CompoundStmt 0x555564f7cfc8 <col:43, line:41:1>
|-DeclStmt 0x555564f7ced8 <line:34:3, col:17>
| `-VarDecl 0x555564f7cef8 <col:3, col:16> col:7 imported in ./thrift_cpp2_base.h hidden referenced result 'Tgt' cinit
| `-IntegerLiteral 0x555564f7d080 <col:16> 'int' 0
|-CallExpr 0x555564f7cea8 <line:39:3, col:76> '<dependent type>'
| |-UnresolvedLookupExpr 0x555564f7bea0 <col:3, col:19> '<overloaded function type>' lvalue (no ADL) = 'then_' 0x555564f7bef0
| |-CXXTemporaryObjectExpr 0x555564f7bcb0 <col:25, col:45> 'Expected<bool, int>':'folly::Expected<bool, int>' 'void () noexcept' zeroing
| `-LambdaExpr 0x555564f7bc88 <col:48, col:75> '(lambda at Conv.h:39:48)'
| |-CXXRecordDecl 0x555564f76b88 <col:48> col:48 imported in ./folly-conv.h hidden implicit <undeserialized declarations> class definition
| | |-also in ./thrift_cpp2_base.h
| | `-DefinitionData lambda empty standard_layout trivially_copyable literal can_const_default_init
| | |-DefaultConstructor defaulted_is_constexpr
| | |-CopyConstructor simple trivial has_const_param needs_implicit implicit_has_const_param
| | |-MoveConstructor exists simple trivial needs_implicit
| | |-CopyAssignment trivial has_const_param needs_implicit implicit_has_const_param
| | |-MoveAssignment
| | `-Destructor simple irrelevant trivial constexpr needs_implicit
| `-CompoundStmt 0x555564f7d1a8 <col:58, col:75>
| `-ReturnStmt 0x555564f7d198 <col:60, col:67>
| `-DeclRefExpr 0x555564f7d0a0 <col:67> 'Tgt' lvalue Var 0x555564f7d0c8 'result' 'Tgt' refers_to_enclosing_variable_or_capture
`-ReturnStmt 0x555564f7bc78 <line:40:3, col:11>
`-InitListExpr 0x555564f7bc38 <col:10, col:11> 'void'
```
This diff changes AST deserialization to load lambdas inside canonical
function declaration earlier right after the function to make sure that
their canonical decl is loaded from the same module.

Test Plan: check-clang

show more ...