[LLDB] Fix 'std::out_of_range' crashing bug when file name completion…

… using file path.

When I run a lldb command that uses filename completion, if I enter a string
that is not only a filename but also a string with a non-file name string added,
such as "./" that is relative path string , it will crash as soon as I press the
[Tab] key. For example, debugging an executable file named "hello" that is
compiled from a file named "hello.c" , and I’ll put a breakpoint on line 3 of
hello.c.

```
$ lldb ./hello
(lldb) breakpoint set --file hello.c --line 3
```

This is not a problem, but if I set "--file ./hello."  and then press [Tab] key
to complete file name, lldb crashes.

```
$ lldb ./hello
(lldb) breakpoint set --file ./hello.terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 8) > this->size() (which is 7)
```

The crash was caused because substr() (in lldb/source/Host/common/Editline.cpp)
cut out string which size is user's input string from the completion string.

I modified the code that erase the user's intput string from current line and
then add the completion string.

Differential Revision: https://reviews.llvm.org/D108817

lldb/source/Host/common/Editline.cpp

@@ -1006,11 +1006,11 @@ unsigned char Editline::TabCommand(int ch) {
     switch (completion.GetMode()) {
     case CompletionMode::Normal: {
       std::string to_add = completion.GetCompletion();
-      to_add = to_add.substr(request.GetCursorArgumentPrefix().size());
       // Terminate the current argument with a quote if it started with a quote.
       if (!request.GetParsedLine().empty() && request.GetParsedArg().IsQuoted())
         to_add.push_back(request.GetParsedArg().GetQuoteChar());
       to_add.push_back(' ');
+      el_deletestr(m_editline, request.GetCursorArgumentPrefix().size());
       el_insertstr(m_editline, to_add.c_str());
       // Clear all the autosuggestion parts if the only single space can be completed.
       if (to_add == " ")

lldb/test/API/iohandler/completion/Makefile

@@ -0,0 +1,3 @@
+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/iohandler/completion/TestIOHandlerCompletion.py

@@ -20,7 +20,8 @@ class IOHandlerCompletionTest(PExpectTest):
     @expectedFailureAll(oslist=['freebsd'], bugnumber='llvm.org/pr49408')
     @skipIf(oslist=["linux"], archs=["arm", "aarch64"])
     def test_completion(self):
-        self.launch(dimensions=(100,500))
+        self.build()
+        self.launch(dimensions=(100,500), executable=self.getBuildArtifact("a.out"))
 
         # Start tab completion, go to the next page and then display all with 'a'.
         self.child.send("\t\ta")
@@ -51,6 +52,13 @@ def test_completion(self):
         self.child.send("\n")
         self.expect_prompt()
 
+        # Complete a file path.
+        # FIXME: This should complete to './main.c' and not 'main.c'
+        self.child.send("breakpoint set --file ./main\t")
+        self.child.expect_exact("main.c")
+        self.child.send("\n")
+        self.expect_prompt()
+
         # Start tab completion and abort showing more commands with 'n'.
         self.child.send("\t")
         self.child.expect_exact("More (Y/n/a)")