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Merge pull request #17857 from geoffw0/unreachable3

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Rust: Fix rust/dead-code
This commit is contained in:
Tom Hvitved
2024-10-29 13:35:10 +01:00
committed by GitHub
parent 879cb7c365 6a110368a5
commit c5d699cb6b
3 changed files with 54 additions and 60 deletions
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99
rust/ql/src/queries/unusedentities/UnreachableCode.ql
View File

@@ -13,63 +13,62 @@ import codeql.rust.controlflow.ControlFlowGraph
import codeql.rust.controlflow.internal.ControlFlowGraphImpl as ControlFlowGraphImpl
/**
* Holds if `n` is an AST node that's unreachable.
* Successor relation that includes unreachable AST nodes.
*/
private predicate unreachable(AstNode n) {
not n = any(CfgNode cfn).getAstNode() and // reachable nodes
exists(ControlFlowGraphImpl::ControlFlowTree cft |
// nodes intended to be part of the CFG
cft.succ(n, _, _)
or
cft.succ(_, n, _)
private predicate succ(AstNode a, AstNode b) {
exists(ControlFlowGraphImpl::ControlFlowTree cft | cft.succ(a, b, _))
}
/**
* Gets a node we'd prefer not to report as unreachable. These will be removed
* from the AST for the purposes of this query, with successor links being
* made across them where appropriate.
*/
predicate hiddenNode(AstNode n) {
// isolated node (not intended to be part of the CFG)
not succ(n, _) and
not succ(_, n)
or
n instanceof ControlFlowGraphImpl::PostOrderTree // location is counter-intuitive
}
/**
* Successor relation for edges out of `hiddenNode`s.
*/
private predicate succHidden(AstNode a, AstNode b) {
hiddenNode(a) and
succ(a, b)
}
/**
* Successor relation that removes / links over `hiddenNode`s.
*/
private predicate succWithHiding(AstNode a, AstNode b) {
exists(AstNode mid |
not hiddenNode(a) and
succ(a, mid) and
succHidden*(mid, b) and
not hiddenNode(b)
)
}
/**
* Holds if `n` is an AST node that's unreachable, and is not the successor
* of an unreachable node (which would be a duplicate result).
* An AST node that is reachable.
*/
predicate reachable(AstNode n) { n = any(CfgNode cfn).getAstNode() }
/**
* Holds if `n` is an AST node that's unreachable, and any predecessors
* of it are reachable (to avoid duplicate results).
*/
private predicate firstUnreachable(AstNode n) {
unreachable(n) and
(
// no predecessor -> we are the first unreachable node.
not ControlFlowGraphImpl::succ(_, n, _)
or
// reachable predecessor -> we are the first unreachable node.
exists(AstNode pred |
ControlFlowGraphImpl::succ(pred, n, _) and
not unreachable(pred)
)
)
not reachable(n) and
not hiddenNode(n) and
forall(AstNode pred | succWithHiding(pred, n) | reachable(pred))
}
/**
* Gets a node we'd prefer not to report as unreachable.
*/
predicate skipNode(AstNode n) {
n instanceof ControlFlowGraphImpl::PostOrderTree or // location is counter-intuitive
not n instanceof ControlFlowGraphImpl::ControlFlowTree // not expected to be reachable
}
/**
* Gets the `ControlFlowTree` successor of a node we'd prefer not to report.
*/
AstNode skipSuccessor(AstNode n) {
skipNode(n) and
ControlFlowGraphImpl::succ(n, result, _)
}
/**
* Gets the node `n`, skipping past any nodes we'd prefer not to report.
*/
AstNode skipSuccessors(AstNode n) {
result = skipSuccessor*(n) and
not skipNode(result)
}
from AstNode first, AstNode report
from AstNode n
where
firstUnreachable(first) and
report = skipSuccessors(first) and
exists(report.getFile().getRelativePath()) // in source
select report, "This code is never reached."
firstUnreachable(n) and
exists(n.getFile().getRelativePath()) // in source
select n, "This code is never reached."

5
rust/ql/test/query-tests/unusedentities/UnreachableCode.expected
View File

@@ -5,7 +5,6 @@
| unreachable.rs:61:2:61:16 | ExprStmt | This code is never reached. |
| unreachable.rs:107:16:107:23 | ExprStmt | This code is never reached. |
| unreachable.rs:115:15:115:22 | ExprStmt | This code is never reached. |
| unreachable.rs:131:2:131:16 | ExprStmt | This code is never reached. |
| unreachable.rs:141:2:141:16 | ExprStmt | This code is never reached. |
| unreachable.rs:148:3:148:17 | ExprStmt | This code is never reached. |
| unreachable.rs:157:4:157:18 | ExprStmt | This code is never reached. |
@@ -13,9 +12,5 @@
| unreachable.rs:169:4:169:18 | ExprStmt | This code is never reached. |
| unreachable.rs:177:4:177:18 | ExprStmt | This code is never reached. |
| unreachable.rs:180:2:180:16 | ExprStmt | This code is never reached. |
| unreachable.rs:197:2:197:16 | ExprStmt | This code is never reached. |
| unreachable.rs:203:3:203:17 | ExprStmt | This code is never reached. |
| unreachable.rs:206:2:206:16 | ExprStmt | This code is never reached. |
| unreachable.rs:218:3:218:17 | ExprStmt | This code is never reached. |
| unreachable.rs:233:2:233:16 | ExprStmt | This code is never reached. |
| unreachable.rs:242:2:242:16 | ExprStmt | This code is never reached. |

10
rust/ql/test/query-tests/unusedentities/unreachable.rs
View File

@@ -128,7 +128,7 @@ fn unreachable_match() {
do_something();
}
}
do_something(); // [unreachable FALSE POSITIVE]
do_something();
match get_a_number() {
1=>{
@@ -194,7 +194,7 @@ fn unreachable_let_1() {
do_something();
}
do_something(); // SPURIOUS: unreachable code
do_something();
if let _ = get_a_number() { // (always succeeds)
do_something();
@@ -203,7 +203,7 @@ fn unreachable_let_1() {
do_something(); // BAD: unreachable code
}
do_something(); // BAD: unreachable code
do_something();
}
fn unreachable_let_2() {
@@ -230,7 +230,7 @@ fn unreachable_if_2() {
do_something();
}
do_something(); // SPURIOUS: unreachable code
do_something();
}
fn unreachable_if_3() {
@@ -239,5 +239,5 @@ fn unreachable_if_3() {
return;
}
do_something(); // SPURIOUS: unreachable code
do_something();
}