Merge pull request #21957 from owen-mc/go/fix-result-node

Go: fix `DataFlow::ResultNode` and some related things

Author: owen-mc

go/ql/lib/change-notes/2026-06-08-deprecate-functypeexpr-getresultdecl.md

@@ -0,0 +1,4 @@
+---
+category: deprecated
+---
+* `FuncTypeExpr.getResultDecl()` has been deprecated. Use `FuncTypeExpr.getResultDecl(int i)` instead.

go/ql/lib/change-notes/2026-06-08-fix-result-nodes.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* `DataFlow::ResultNode`s are no longer created for returned expressions in functions with named result parameters. In this case there are already result nodes corresponding to `IR::ReadResultInstruction`s at the end of the function body.

go/ql/lib/change-notes/2026-06-08-functypeexpr-getnumresult.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* `FuncTypeExpr.getNumResult()` now gets the number of result parameters. It previously got the number of result declarations, which is different when one result declaration declares more than one variable, as in `x, y int`. All uses of it expected the number of result parameters. Its QLDoc has been updated.

go/ql/lib/semmle/go/Expr.qll

@@ -1049,17 +1049,29 @@ class FuncTypeExpr extends @functypeexpr, TypeExpr, ScopeNode, FieldParent {
    */
   int getNumParameter() { result = count(this.getAParameterDecl().getANameExpr()) }
 
-  /** Gets the `i`th result of this function type (0-based). */
+  /**
+   * Gets the `i`th result declaration of this function type (0-based).
+   *
+   * Note: `x, y int` is a single `ResultVariableDecl`.
+   */
   ResultVariableDecl getResultDecl(int i) { result = this.getField(-(i + 1)) }
 
-  /** Gets a result of this function type. */
+  /**
+   * Gets a result declaration of this function type.
+   *
+   * Note: `x, y int` is a single `ResultVariableDecl`.
+   */
   ResultVariableDecl getAResultDecl() { result = this.getResultDecl(_) }
 
-  /** Gets the number of results of this function type. */
-  int getNumResult() { result = count(this.getAResultDecl()) }
+  /** Gets the number of result parameters of this function type. */
+  int getNumResult() { result = count(this.getAResultDecl().getANameExpr()) }
 
-  /** Gets the result of this function type, if there is only one. */
-  ResultVariableDecl getResultDecl() { this.getNumResult() = 1 and result = this.getAResultDecl() }
+  /**
+   * DEPRECATED: Use `getResultDecl(int i)` instead.
+   */
+  deprecated ResultVariableDecl getResultDecl() {
+    this.getNumResult() = 1 and result = this.getAResultDecl()
+  }
 
   override string toString() { result = "function type" }
 

go/ql/lib/semmle/go/dataflow/internal/DataFlowNodes.qll

@@ -923,15 +923,20 @@ module Public {
   /**
    * A node whose value is returned as a result from a function.
    *
-   * This can either be a node corresponding to an expression in a return statement,
-   * or a node representing the current value of a named result variable at the exit
-   * of the function.
+   * If the function declares named result variables, this is a node representing
+   * the current value of one of those variables at function exit. Otherwise, this
+   * is a node corresponding to an expression in a return statement.
    */
   class ResultNode extends InstructionNode {
     int i;
 
     ResultNode() {
       exists(FuncDef fd |
+        // If the function has named result variables, then the
+        // `IR::ReadResultInstruction` nodes at the end of the function are
+        // the correct result nodes. Otherwise, the returned expressions are
+        // the result nodes.
+        not exists(fd.getAResultVar()) and
         exists(IR::ReturnInstruction ret | ret.getRoot() = fd | insn = ret.getResult(i))
         or
         insn.(IR::ReadResultInstruction).reads(fd.getResultVar(i))

go/ql/test/library-tests/semmle/go/controlflow/ControlFlowGraph/ControlFlowNode_getASuccessor.expected

@@ -53,6 +53,16 @@ func baz2() (result int) {
 	return
 }
 
+func baz3(selector int) (result int) {
+	result = 0
+	if selector == 1 {
+		return 1
+	} else {
+		result = 2
+	}
+	return
+}
+
 func loops() {
 	var x int
 	for cond() {

go/ql/test/library-tests/semmle/go/controlflow/ControlFlowGraph/main.go

@@ -2,3 +2,5 @@
 | main.go:7:19:7:23 | ...+... | + | main.go:7:19:7:19 | y | main.go:7:23:7:23 | z |
 | main.go:10:14:10:18 | ...+... | + | main.go:10:14:10:14 | x | main.go:10:18:10:18 | y |
 | main.go:17:2:17:13 | ... += ... | + | main.go:17:2:17:6 | index expression | main.go:17:11:17:13 | "!" |
+| resultParameters.go:4:5:4:17 | ...==... | == | resultParameters.go:4:5:4:12 | selector | resultParameters.go:4:17:4:17 | 0 |
+| resultParameters.go:23:5:23:17 | ...==... | == | resultParameters.go:23:5:23:12 | selector | resultParameters.go:23:17:23:17 | 1 |

go/ql/test/library-tests/semmle/go/dataflow/Nodes/BinaryOperationNodes.expected

@@ -0,0 +1,8 @@
+| main.go:21:9:21:10 | 23 | Result node with index 0 |
+| main.go:21:13:21:14 | 42 | Result node with index 1 |
+| resultParameters.go:5:10:5:10 | 0 | Result node with index 0 |
+| resultParameters.go:9:10:9:10 | 1 | Result node with index 0 |
+| resultParameters.go:11:10:11:10 | 2 | Result node with index 0 |
+| resultParameters.go:13:9:13:9 | 3 | Result node with index 0 |
+| resultParameters.go:16:26:16:26 | implicit read of r | Result node with index 0 |
+| resultParameters.go:21:38:21:38 | implicit read of r | Result node with index 0 |

go/ql/test/library-tests/semmle/go/dataflow/Nodes/ResultNode.expected

@@ -0,0 +1,9 @@
+/**
+ * @kind problem
+ * @id result-node
+ */
+
+import go
+
+from DataFlow::ResultNode r
+select r, "Result node with index " + r.getIndex()