add getEnclosingBlock for Go

[Lslightly]

codeql/go/ql/lib/semmle/go/AST.qll

Lines 77 to 85 in 6fa6093

	/** Gets the parent node of this AST node, but without crossing function boundaries. */
	private AstNode parentInSameFunction() {
	result = this.getParent() and
	not this instanceof FuncDef
	}
	/** Gets the innermost function definition to which this AST node belongs, if any. */
	pragma[nomagic]
	FuncDef getEnclosingFunction() { result = this.getParent().parentInSameFunction*() }

In rust and cpp, getEnclosingBlock is supported as shown by search result. Would Go support this?

  /** Gets the parent node of this AST node, but without crossing block boundaries. */
  private AstNode parentInSameBlock() {
    result = this.getParent() and
    not this instanceof BlockStmt
  }

  /** Gets the innermost block statement to which this AST node belongs, if any. */
  pragma[nomagic]
  FuncDef getEnclosingBlock() { result = this.getParent().parentInSameBlock*() }

[owen-mc]

Can I ask what you want to use it for?

The two examples you give are very much about syntactic blocks. Both of those languages have a BlockExpr or BlockStmt in their AST, which we don't have in the Go AST. We have something a bit similar in go: getEnclosingBlock on ControlFlow::Node, which returns a BasicBlock. But it uses the control flow graph, so it goes beyond the AST level to what is actually happening semantically. To see the difference, consider this function:

func f() {
    g()
    h()
}

At a syntactic level it clearly has one block. But from the point of the view of control flow it has two basic blocks, because g might panic, in which case h would not be called after it.

[Lslightly]

Usage Scenario: decide whether the declaration of obj is in the same BlockStmt as GoStmt and assert that obj will not be accessed after GoStmt in execution(or semantically).

var obj S
go func() { access(obj) }()

If they are not in same BlockStmt, then usually obj is declared in outer BlockStmt.

var obj S
for {
  go func() { access(obj) }()
}

Both of those languages have a BlockExpr or BlockStmt in their AST, which we don't have in the Go AST

go-all package(4.2.5 version) in codeql v2.21.3 codeql qlpacks have BlockStmt. I also checked the latest codeql packs. BlockStmt exists. What do you mean by "which we don't have in the Go AST"?

We have something a bit similar in go: getEnclosingBlock on ControlFlow::Node

Thanks for your explanation! In the second example above, using AST level getEnclosingBlock to decide that obj might be used in later iteration is fast and simple, because I can easily get the GoStmt which references obj. The obj is categorized as class MovedToHeapVar extends LocalVariable by Location, which is provided by external predicates.

I will try to connect ControlFlow::Node with GoStmt and declaration Ident and use getASuccessor to assert that obj will not be accessed after GoStmt. But I doubt that it can be complex.