[Clang] Fix the for statement disappearing in AST when an error occurs in the conditional expression of the for statement

[yronglin]

Consider:

constexpr int f() {
    int sum = 0;
    for (int i = 0; undefined_var; ++i) {
        sum += i;
    }
    return sum;
}

static_assert(f());

The AST before this patch:

|-FunctionDecl <line:1:1, line:7:1> line:1:15 used constexpr f 'int ()' implicit-inline
| `-CompoundStmt <col:19, line:7:1>
|   |-DeclStmt <line:2:5, col:16>
|   | `-VarDecl <col:5, col:15> col:9 used sum 'int' cinit
|   |   `-IntegerLiteral <col:15> 'int' 0
|   `-ReturnStmt <line:6:5, col:12>
|     `-ImplicitCastExpr <col:12> 'int' <LValueToRValue>
|       `-DeclRefExpr <col:12> 'int' lvalue Var 0xb870518 'sum' 'int'

The AST after this patch:

|-FunctionDecl 0x11d0f63f8 <./main.cpp:1:1, line:7:1> line:1:15 used constexpr f 'int ()' implicit-inline
| `-CompoundStmt 0x11d110880 <col:19, line:7:1>
|   |-DeclStmt 0x11d0f65c8 <line:2:5, col:16>
|   | `-VarDecl 0x11d0f6528 <col:5, col:15> col:9 used sum 'int' cinit
|   |   `-IntegerLiteral 0x11d0f6590 <col:15> 'int' 0
|   |-ForStmt 0x11d110800 <line:3:5, line:5:5>
|   | |-DeclStmt 0x11d0f66a0 <line:3:10, col:19>
|   | | `-VarDecl 0x11d0f6600 <col:10, col:18> col:14 used i 'int' cinit
|   | |   `-IntegerLiteral 0x11d0f6668 <col:18> 'int' 0
|   | |-<<<NULL>>>
|   | |-RecoveryExpr 0x11d0f66e8 <col:21> 'bool' contains-errors
|   | |-UnaryOperator 0x11d0f6728 <col:36, col:38> 'int' lvalue prefix '++'
|   | | `-DeclRefExpr 0x11d0f6708 <col:38> 'int' lvalue Var 0x11d0f6600 'i' 'int'
|   | `-CompoundStmt 0x11d0f67c8 <col:41, line:5:5>
|   |   `-CompoundAssignOperator 0x11d0f6798 <line:4:9, col:16> 'int' lvalue '+=' ComputeLHSTy='int' ComputeResultTy='int'
|   |     |-DeclRefExpr 0x11d0f6740 <col:9> 'int' lvalue Var 0x11d0f6528 'sum' 'int'
|   |     `-ImplicitCastExpr 0x11d0f6780 <col:16> 'int' <LValueToRValue>
|   |       `-DeclRefExpr 0x11d0f6760 <col:16> 'int' lvalue Var 0x11d0f6600 'i' 'int'
|   `-ReturnStmt 0x11d110870 <line:6:5, col:12>
|     `-ImplicitCastExpr 0x11d110858 <col:12> 'int' <LValueToRValue>
|       `-DeclRefExpr 0x11d110838 <col:12> 'int' lvalue Var 0x11d0f6528 'sum' 'int'

[yronglin]

Can we use ParseParenExprOrCondition here? but it may need to extend the parameters of ParseParenExprOrCondition .

[shafik]

This looks good to me but I would like another set of eyes on it.

[cor3ntin]

LGTM modulo @shafik's feedback

[yronglin]

Thanks for the review! @cor3ntin @shafik , wait for CI green.