[llvm-bugs] [Bug 45790] New: Changing behavior in clang::SourceRange.getEnd() between clang versions 8 and 9 and later

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45790

            Bug ID: 45790
           Summary: Changing behavior in clang::SourceRange.getEnd()
                    between clang versions 8 and 9 and later
           Product: clang
           Version: 9.0
          Hardware: PC
                OS: FreeBSD
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: lunkov at gmail.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Created attachment 23439
  --> https://bugs.llvm.org/attachment.cgi?id=23439&action=edit
Test file

I encountered a backward compatibility violation in the
clang::SourceRange.getEnd() between versions 8 and 9 in the following code:

------
void MyPPCallbacks::If(SourceLocation Loc, SourceRange ConditionRange,
ConditionValueKind ConditionValue){
        [...]
        StartPos = SM.getFileOffset(SM.getFileLoc(Loc));
        EndPos = SM.getFileOffset(SM.getFileLoc(ConditionRange.getEnd()));
        [...]
}
------

This code has worked without changing behavior since clang version 3.4.
In clang version 8.0, EndPos is ALWAYS equal to the position of the macro
character following the last, and in clang version 9.0 and later EndPos takes
on a value depending on the expression.

In the following example, you can see the difference which values EndPos takes
in various expressions in clang 8 and clang 9:

------
#define TEST_MACRO 1

// example 1
#if defined(TEST_MACRO) && !defined(UNDEF_TEST_MACRO)
//                                                   ^ clang 8   
ConditionRange.getEnd().getRawEncoding() = 91
//                                                  ^ clang 9   
ConditionRange.getEnd().getRawEncoding() = 90
#endif

// example 2
#if TEST_MACRO && TEST_MACRO
//                          ^ clang 8   
ConditionRange.getEnd().getRawEncoding() = 364
//               ^ clang 9    ConditionRange.getEnd().getRawEncoding() =
2147495546
#endif

// example 3
#if TEST_MACRO
//            ^ clang 8    ConditionRange.getEnd().getRawEncoding() = 572
// ^ clang 9    ConditionRange.getEnd().getRawEncoding() = 2147495548
#endif

int main(){ return 0; }
------

In examples 2 and 3, the value of getRawEncoding() for some reason changes
depending on the length of the file.

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