- Extract names of properties in a propery match, using the `exprorstmt_name` relation.
- Simplify extraction of properties by not distinguishing between top-level patterns
and nested patterns.
- Introduce `PatternExpr` to capture patterns in `is` expressions, `case` statements,
and `switch` expression arms.
- Generalize `IsTypeExpr`, `IsPatternExpr`, `IsRecursivePatternExpr`, and `IsConstantExpr`
to just `IsExpr` with a member predicate `PatternExpr getPattern()`.
- Generalize `TypeCase`, `RecursivePatternCase`, and `ConstCase` to just `CaseStmt` with
a member predicate `PatternExpr getPattern()`.
- Introduce classes `Switch` and `Case` as base classes of switch statements/expressions
and case statements/switch expression arms, respectively.
- Simplify CFG logic using the generalized classes.
- Generalize guards library to cover `switch` expressions tests.
- Generalize data flow library to cover `switch` expression assignments.
- Cache predicates in the same stage using a cached module.
- Introduce `DefUse::defUseVariableUpdate()` and use in `CallableReturns.qll`.
The updated file `csharp/ql/test/library-tests/cil/dataflow/Nullness.expected`
demonstrates why this is needed.
- Utilize CIL analysis in `Guards::nonNullValue()`.
- Analyze SSA definitions in `AlwaysNullExpr`, similar to `NonNullExpr`.
Write accesses in assignments, such as the access to `x` in `x = 0` are not
evaluated, so they should not have entries in the control flow graph. However,
qualifiers (and indexer arguments) should still be evaluated, for example in
```
x.Foo.Bar = 0;
```
the CFG should be `x --> x.Foo --> 0 --> x.Foo.Bar = 0` (as opposed to
`x --> x.Foo --> x.Foo.Bar --> 0 --> x.Foo.Bar = 0`, prior to this change).
A special case is assignments via acessors (properties, indexers, and event
adders), where we do want to include the access in the control flow graph,
as it represents the accessor call:
```
x.Prop = 0;
```
But instead of `x --> x.set_Prop --> 0 --> x.Prop = 0` the CFG should be
`x --> 0 --> x.set_Prop --> x.Prop = 0`, as the setter is called *after* the
assigned value has been evaluated.
An even more special case is tuple assignments via accessors:
```
(x.Prop1, y.Prop2) = (0, 1);
```
Here the CFG should be
`x --> y --> 0 --> 1 --> x.set_Prop1 --> y.set_Prop2 --> (x.Prop1, y.Prop2) = (0, 1)`.
Rewrite the predicate `succSplits()` and the construction of the IPA type `TSplits`.
The two are now mutually dependent, see more in the comment for the module
`SuccSplits`.
A method such as
```
void M()
{
throw new Exception();
}
```
was incorrectly not categorized as a `ThrowingCallable`, that is, a callable
that always throws an exception upon invocation.
For example, in
```
void M(object x)
{
var y = x != null ? "" : null;
if (y != null)
x.ToString();
}
```
the guard `y != null` implies that the guard `x != null` must be true.
The internal pre-SSA library was extended on 3e78c2671f
to include fields/properties that are local-scope-like. The CFG splitting logic
uses ranking of SSA definitions to define an (arbitrary) order of splits, but for
fields/properties the implicit entry definition all have the same line and column.
In effect, such SSA definitions incorrectly get the same rank. Adding the name
of the field/property to the lexicographic ordering resolves the issue.
