[cfe-dev] [Bug Report] Rewriter crashes when compilation database contains files with same name

[HyunSu Lim via cfe-dev]

This is the clang bug report. This bug report is also posted to the [Clang
Bugzilla](https://bugs.llvm.org/show_bug.cgi?id=38270)

# Overview

If the compilation database contains the files with same name but different
path and size, the program written using clang libtooling and clang
Rewriter crashes.

The files that I used to reproduce the bug can be found [here](
https://drive.google.com/open?id=183eG4cvORKlIWwJdPIkQlxE12riKnQaK).
Detailed description of these files are presented in **About Example
Files** section.

# Steps to Reproduce

1) Create the build system that generates the following
`compile_commands.json`:
```json
[
    {
        "arguments": [
            "cc",
            "-c",
            "-o",
            "a.o",
            "a.c"
        ],
        "directory": "/home/user/build_system/lib",
        "file": "a.c"
    },
    {
        "arguments": [
            "cc",
            "-c",
            "-o",
            "a.o",
            "a.c"
        ],
        "directory": "/home/user/build_system/src",
        "file": "a.c"
    }
]
```
In here, the length of the content of `/home/user/build_system/src/a.c`
**should be larger** than that of `/home/user/build_system/lib/a.c`.

2) Create a program with clang libtooling, which reads the compilation
database and for every file in compilation database, does rewriting on
every statement in the file.

3) Run the program on the created compilation database. The program runs
cleanly on `lib/a.c`, but it shows segfault when processing `src/a.c`.


# Actual Results

The program with clang libtooling shows segfault.


# Expected Results

The program with clang libtooling should run cleanly, not showing segfault.


# Tested Environment

 - OS: Ubuntu LTS 16.04 Xenial
 - LLVM Version: 6.0.1


# About Example Files

This section describes the details of files that I [linked](
https://drive.google.com/open?id=183eG4cvORKlIWwJdPIkQlxE12riKnQaK).

- `build_example/`: Example build system
   - `lib/`
      - `a.c`: Example c file (shorter one)
      - `Makefile`: A makefile to compile `a.c`
   - `src/`
      - `a.c`: Example c file (longer one)
      - `Makefile`: A makefile to compile `a.c`
   - `compile_commands.json`: Compilation database. This file is generated
by running the command `$ bear make`
   - `Makefile`: A makefile to build the whole example build system
- `Makefile`: A makefile to build `target.cpp`
- `target.cpp`: A program that uses clang libtooling and clang Rewriter.
This program fails when run on the given compilation database, which
shouldn't


# Other Comments

I also used `clang-check` on `lib/a.c` and `src/a.c` (`$ clang-check
lib/a.c src/a.c`), and it shows errors with `src/a.c` which are not actual
errors.

I think when the `SourceManager` processes `src/a.c`, it uses the buffer
that is created when processing `lib/a.c` (because it has same file name),
and this causes an error.



Thanks.
Hyunsu Lim
-- 
Best Regards,
Hyunsu Lim
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