C#: Include parameters and their defaults in the CFG

[hvitved]

This PR adds support in the shared CFG library for including parameters and their default values, and applies this to C# (even though, technically, default values are inlined into the callers).

We use Matching successors to denote whether an argument has been supplied or not. For example, this C# program

string M1(bool b, string s = "", int i = 0)
{
    return b + s + i;
}

gives rise to the following CFG (skipping the parts inside the body):

flowchart TD
1["Entry"]
10["After i [no-match]"]
11["i"]
12["0"]
13["{...}"]
4["b"]
5["After s [match]"]
6["After s [no-match]"]
7["s"]
8['""']
9["After i [match]"]

1 --> 4
4 --> 7
5 --> 11
6 --> 8
7 -- match --> 5
7 -- no-match --> 6
8 --> 11
9 --> 13
10 --> 12
11 -- match --> 9
11 -- no-match --> 10
12 --> 13

Loading

With parameters and their defaults added to the CFG, we replace existing SSA definitions at function entry with their CFG nodes (except when functions have multiple bodies), and we also add SSA definitions corresponding to defaults, which means that phi nodes will automatically be inserted.

Commit-by-commit review is strongly encouraged.

[hvitved]

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[Copilot]

Pull request overview

This PR extends the shared control-flow graph (CFG) library to include callable parameters and their default values as CFG nodes, and wires that functionality into the C# libraries (including SSA/dataflow integration and schema support).

Changes:

• Extend the shared CFG AST signature with Parameter + callableGetParameter, and model default-argument control flow using Matching successors.
• Update the C# CFG implementation to emit parameter/default nodes, update SSA to create parameter + parameter-default definitions (so phis are inserted naturally), and adjust related dataflow helpers.
• Update the C# dbscheme and add upgrade/downgrade artifacts; update/extend C# CFG & SSA/dataflow tests and expected outputs (including new default-parameter test cases).

Show a summary per file

File	Description
shared/controlflow/codeql/controlflow/ControlFlowGraph.qll	Adds parameter support to the shared CFG library and integrates default-value branching into successor modeling.
java/ql/lib/semmle/code/java/ControlFlowGraph.qll	Adapts Java CFG wiring to the new shared CFG signature (context type rename; parameter stubs).
csharp/ql/test/query-tests/Nullness/NullMaybe.expected	Updates expected nullness output impacted by new parameter/default SSA/CFG modeling.
csharp/ql/test/library-tests/obinit/ObInit.expected	Updates expected CFG output due to parameter nodes being present at callable entry.
csharp/ql/test/library-tests/dataflow/ssa/SsaUltimateDef.expected	Updates SSA ultimate-definition expectations to include parameter/default definitions and phis.
csharp/ql/test/library-tests/dataflow/ssa/SsaRead.expected	Updates SSA read expectations for parameters now represented in SSA/CFG.
csharp/ql/test/library-tests/dataflow/ssa/SsaImplicitParameterDef.ql	Updates test query to use the new parameter-definition class name.
csharp/ql/test/library-tests/dataflow/ssa/SsaImplicitParameterDef.expected	Updates expected results for the renamed/reworked parameter SSA definition representation.
csharp/ql/test/library-tests/dataflow/ssa/SsaExplicitDef.expected	Updates expected explicit-def results reflecting parameter SSA defs now emitted.
csharp/ql/test/library-tests/dataflow/ssa/SsaDefElement.expected	Updates expected def-element results for parameter/default SSA def elements.
csharp/ql/test/library-tests/dataflow/ssa/SsaDef.expected	Updates expected SSA defs to include parameter/default defs and phis.
csharp/ql/test/library-tests/dataflow/ssa/SSAPhi.expected	Updates expected phi nodes created due to parameter/default merge points.
csharp/ql/test/library-tests/dataflow/ssa/DefaultParam.cs	New SSA test case for default parameters.
csharp/ql/test/library-tests/dataflow/ssa/DefAdjacentRead.expected	Updates adjacency expectations due to parameter node introduction.
csharp/ql/test/library-tests/dataflow/ssa/BaseSsaConsistency.ql	Updates SSA consistency test to refer to the new parameter-definition type.
csharp/ql/test/library-tests/dataflow/local/TaintTrackingStep.expected	Updates expected local taint-tracking step output for default-parameter flow.
csharp/ql/test/library-tests/dataflow/local/TaintTracking.expected	Updates expected local taint-tracking alerts to include default-parameter cases.
csharp/ql/test/library-tests/dataflow/local/LocalDataFlow.cs	Adds a default-parameter dataflow test method.
csharp/ql/test/library-tests/dataflow/local/DataFlowStep.expected	Updates expected local dataflow-step output for default-parameter flow.
csharp/ql/test/library-tests/dataflow/local/DataFlow.expected	Updates expected local dataflow results to include default-parameter cases.
csharp/ql/test/library-tests/dataflow/defuse/parameterUseEquivalence.ql	Updates def-use equivalence test to use the new parameter-definition type.
csharp/ql/test/library-tests/dataflow/defuse/defUseEquivalence.ql	Updates equivalence logic to account for parameter CFG nodes when computing reachability.
csharp/ql/test/library-tests/csharp8/switchexprcontrolflow.expected	Updates expected CFG output due to parameter nodes at entry.
csharp/ql/test/library-tests/csharp7/DefUse.ql	Updates SSA def-use test to use the new parameter-definition type.
csharp/ql/test/library-tests/controlflow/graph/Nodes.expected	Updates expected CFG node listing to include parameters as CFG elements.
csharp/ql/test/library-tests/controlflow/graph/DefaultParam.cs	New CFG test case for default parameters.
csharp/ql/test/library-tests/controlflow/graph/Condition.expected	Adds expected conditional edges for default-parameter “match/no-match” successors.
csharp/ql/lib/upgrades/19b8cc3e2dc768d4cbc03d6e3773b709bbebd036/upgrade.properties	Adds a C# database upgrade for schema change related to parameters as CFG elements.
csharp/ql/lib/upgrades/19b8cc3e2dc768d4cbc03d6e3773b709bbebd036/old.dbscheme	Upgrade scaffolding for the dbscheme change (dummy line approach).
csharp/ql/lib/semmlecode.csharp.dbscheme	Extends @control_flow_element to include @parameter.
csharp/ql/lib/semmle/code/csharp/dataflow/internal/SsaImpl.qll	Updates SSA internals to represent parameter entry/default defs and handle multi-body callables.
csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll	Adjusts internal dataflow helpers to reflect parameter CFG nodes and multi-body behavior.
csharp/ql/lib/semmle/code/csharp/dataflow/SSA.qll	Exposes/renames parameter SSA definitions, adds parameter-default SSA definitions, updates doc/comments accordingly.
csharp/ql/lib/semmle/code/csharp/dataflow/Nullness.qll	Updates nullness analysis to use the new parameter-definition type and removes old “null default” special-casing.
csharp/ql/lib/semmle/code/csharp/controlflow/internal/ControlFlowGraph.qll	New internal C# AST/CFG wiring module implementing parameters + default values for shared CFG.
csharp/ql/lib/semmle/code/csharp/controlflow/Guards.qll	Updates guard logic to use the new parameter-definition type.
csharp/ql/lib/semmle/code/csharp/controlflow/ControlFlowGraph.qll	Switches to the new internal CFG module and updates callable-context plumbing.
csharp/ql/lib/semmle/code/csharp/Variable.qll	Makes Parameter a ControlFlowElement to align with new CFG modeling.
csharp/ql/lib/semmle/code/csharp/PrintAst.qll	Excludes parameters from generic ControlFlowElement printing (handled by a dedicated node).
csharp/ql/lib/semmle/code/csharp/ExprOrStmtParent.qll	Adjusts parent/child hierarchy to accommodate parameters as top-level expression parents and CFG elements.
csharp/ql/lib/semmle/code/csharp/Assignable.qll	Adds an assignable-definition for parameter default values and aligns assignable/SSA integration.
csharp/ql/lib/printCfg.ql	Updates CFG printing query imports/types for the new internal CFG module and callable type usage.
csharp/downgrades/a5765bf26f38b38424eeb97f83104b5f5b41db0d/upgrade.properties	Adds downgrade metadata to revert parameters-as-control-flow-elements schema change.
csharp/downgrades/a5765bf26f38b38424eeb97f83104b5f5b41db0d/old.dbscheme	Downgrade scaffolding for the dbscheme change.

Copilot's findings

• Files reviewed: 49/51 changed files
• Comments generated: 1

[Copilot]

Grammar: change "to gets" to "to get" in this comment.

Suggested change

	// In case `c` has multiple bodies, we want each body to gets its own implicit
	// In case `c` has multiple bodies, we want each body to get its own implicit