Format specifiers are wrongly stripped from -exec commands

[gareth-rees]

When entering an -exec command in the DEBUG CONSOLE in Visual Studio Code, I expect the remainder of the command to be passed as-is to GDB. In particular, if I enter the command

-exec echo abc,d

then I expect GDB to execute the command echo abc,d, producing the output abc,d in the DEBUG CONSOLE. But what I see instead is the output abc without the ,d. See screenshot below (using Visual Studio Code 1.64.2 and C/C++ extension v1.8.4):

The chain of calls that lead to this bug is:

1. AD7DebugSession.HandleEvaluateRequestAsync receives expression="-exec echo abc,d" and calls:

   MIEngine/src/OpenDebugAD7/AD7DebugSession.cs

   Line 2918 in a109b93

   hr = expressionContext.ParseText(expression, enum_PARSEFLAGS.PARSE_EXPRESSION, Constants.ParseRadix, out expressionObject, out error, out errorIndex);

2. IDebugExpression2.ParseText receives pszCode="-exec echo abc,d" and calls:

   MIEngine/src/MIDebugEngine/AD7.Impl/AD7StackFrame.cs

   Line 595 in a109b93

   ppExpr = new AD7Expression(Engine, Engine.DebuggedProcess.Natvis.GetVariable(pszCode, this));

3. GetVariable receives expr="-exec echo abc,d" and calls:

   MIEngine/src/MIDebugEngine/Natvis.Impl/Natvis.cs

   Line 441 in a109b93

   variable = new VariableInformation(expr, expr, frame.ThreadContext, frame.Engine, frame.Thread);

4. The VariableInformation constructor receives expr="-exec echo abc,d" and calls:

   MIEngine/src/MIDebugEngine/Engine.Impl/Variables.cs

   Line 216 in a109b93

   _strippedName = StripFormatSpecifier(expr, out _format);

5. StripFormatSpecifier receives exp="-exec echo abc,d" and strips the ,d by executing:

   MIEngine/src/MIDebugEngine/Engine.Impl/Variables.cs

   Line 421 in a109b93

   return exp.Substring(0, lastComma);

Note that the code in AD7DebugSession.HandleEvaluateRequestAsync already tests for the -exec case:

MIEngine/src/OpenDebugAD7/AD7DebugSession.cs

Lines 2863 to 2865 in a109b93

	// If this is an -exec command (or starts with '`') treat it as a console command and log telemetry
	if (expression.StartsWith("-exec", StringComparison.Ordinal) || expression[0] == '`')
	isExecInConsole = true;

but this context has been lost by the time we get to the StripFormatSpecifier call.

Solution ideas:

1. Pass the isExecInConsole flag down through ParseText and GetVariable to the VariableInformation constructor which can use it to skip the StripFormatSpecifier call. The problem with this approach is that ParseText implements the IDebugExpressionContext2::ParseText interface which we can't change.

2. Test the -exec and backtick cases again inside StripFormatSpecifier and avoid stripping the specifier if these are found. The problem with this is that the test gets duplicated and so there is a risk of changing it in one place and not the other. Also, might there be a legitimate expression starting with -exec (meaning the negation of the value of a variable starting exec).

3. Append a comma to expression in HandleEvaluateRequestAsync whose only purpose is to be stripped by StripFormatSpecifier.

I will prepare a pull request implementing solution (3) but if you have a better suggestion then let me know.