Add test showing limits of DeferStmt in CFG

There are paths to the exit of the function which go through the defer
statement and paths which don't, so we add an optional call to the
deferred function. This causes FPs in the query as it stands.

Author: owen-mc

go/ql/test/query-tests/InconsistentCode/UnhandledCloseWritableHandle/UnhandledCloseWritableHandle.expected

@@ -5,9 +5,10 @@
 | tests.go:15:3:15:3 | f | tests.go:46:5:46:76 | ... := ...[0] | tests.go:15:3:15:3 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:46:15:46:76 | call to OpenFile | call to OpenFile |
 | tests.go:57:3:57:3 | f | tests.go:55:5:55:78 | ... := ...[0] | tests.go:57:3:57:3 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:55:15:55:78 | call to OpenFile | call to OpenFile |
 | tests.go:69:3:69:3 | f | tests.go:67:5:67:76 | ... := ...[0] | tests.go:69:3:69:3 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:67:15:67:76 | call to OpenFile | call to OpenFile |
-| tests.go:111:9:111:9 | f | tests.go:109:5:109:78 | ... := ...[0] | tests.go:111:9:111:9 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:109:15:109:78 | call to OpenFile | call to OpenFile |
-| tests.go:130:3:130:3 | f | tests.go:126:5:126:78 | ... := ...[0] | tests.go:130:3:130:3 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:126:15:126:78 | call to OpenFile | call to OpenFile |
-| tests.go:151:8:151:8 | f | tests.go:147:2:147:74 | ... := ...[0] | tests.go:151:8:151:8 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:147:12:147:74 | call to OpenFile | call to OpenFile |
+| tests.go:112:9:112:9 | f | tests.go:109:5:109:78 | ... := ...[0] | tests.go:112:9:112:9 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:109:15:109:78 | call to OpenFile | call to OpenFile |
+| tests.go:126:9:126:9 | f | tests.go:124:5:124:78 | ... := ...[0] | tests.go:126:9:126:9 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:124:15:124:78 | call to OpenFile | call to OpenFile |
+| tests.go:145:3:145:3 | f | tests.go:141:5:141:78 | ... := ...[0] | tests.go:145:3:145:3 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:141:15:141:78 | call to OpenFile | call to OpenFile |
+| tests.go:166:8:166:8 | f | tests.go:162:2:162:74 | ... := ...[0] | tests.go:166:8:166:8 | f | File handle may be writable as a result of data flow from a $@ and closing it may result in data loss upon failure, which is not handled explicitly. | tests.go:162:12:162:74 | call to OpenFile | call to OpenFile |
 edges
 | tests.go:9:24:9:24 | definition of f | tests.go:10:8:10:8 | f | provenance |  |
 | tests.go:13:32:13:32 | definition of f | tests.go:14:13:16:2 | capture variable f | provenance |  |
@@ -22,9 +23,10 @@ edges
 | tests.go:48:29:48:29 | f | tests.go:13:32:13:32 | definition of f | provenance |  |
 | tests.go:55:5:55:78 | ... := ...[0] | tests.go:57:3:57:3 | f | provenance | Src:MaD:1  |
 | tests.go:67:5:67:76 | ... := ...[0] | tests.go:69:3:69:3 | f | provenance | Src:MaD:1  |
-| tests.go:109:5:109:78 | ... := ...[0] | tests.go:111:9:111:9 | f | provenance | Src:MaD:1  |
-| tests.go:126:5:126:78 | ... := ...[0] | tests.go:130:3:130:3 | f | provenance | Src:MaD:1  |
-| tests.go:147:2:147:74 | ... := ...[0] | tests.go:151:8:151:8 | f | provenance | Src:MaD:1  |
+| tests.go:109:5:109:78 | ... := ...[0] | tests.go:112:9:112:9 | f | provenance | Src:MaD:1  |
+| tests.go:124:5:124:78 | ... := ...[0] | tests.go:126:9:126:9 | f | provenance | Src:MaD:1  |
+| tests.go:141:5:141:78 | ... := ...[0] | tests.go:145:3:145:3 | f | provenance | Src:MaD:1  |
+| tests.go:162:2:162:74 | ... := ...[0] | tests.go:166:8:166:8 | f | provenance | Src:MaD:1  |
 models
 | 1 | Source: os; ; false; OpenFile; ; ; ReturnValue[0]; file; manual |
 nodes
@@ -44,9 +46,11 @@ nodes
 | tests.go:67:5:67:76 | ... := ...[0] | semmle.label | ... := ...[0] |
 | tests.go:69:3:69:3 | f | semmle.label | f |
 | tests.go:109:5:109:78 | ... := ...[0] | semmle.label | ... := ...[0] |
-| tests.go:111:9:111:9 | f | semmle.label | f |
-| tests.go:126:5:126:78 | ... := ...[0] | semmle.label | ... := ...[0] |
-| tests.go:130:3:130:3 | f | semmle.label | f |
-| tests.go:147:2:147:74 | ... := ...[0] | semmle.label | ... := ...[0] |
-| tests.go:151:8:151:8 | f | semmle.label | f |
+| tests.go:112:9:112:9 | f | semmle.label | f |
+| tests.go:124:5:124:78 | ... := ...[0] | semmle.label | ... := ...[0] |
+| tests.go:126:9:126:9 | f | semmle.label | f |
+| tests.go:141:5:141:78 | ... := ...[0] | semmle.label | ... := ...[0] |
+| tests.go:145:3:145:3 | f | semmle.label | f |
+| tests.go:162:2:162:74 | ... := ...[0] | semmle.label | ... := ...[0] |
+| tests.go:166:8:166:8 | f | semmle.label | f |
 subpaths

go/ql/test/query-tests/InconsistentCode/UnhandledCloseWritableHandle/tests.go

@@ -104,6 +104,21 @@ func deferredCloseWithSync() {
 	}
 }
 
+func deferredCloseWithSync2() {
+	// open file for writing
+	if f, err := os.OpenFile("foo.txt", os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0666); err != nil { // $ SPURIOUS: Source
+		// a call to `Close` is deferred, but we have a call to `Sync` later which
+		// precedes the call to `Close` during execution
+		defer f.Close() // $ SPURIOUS: Alert
+
+		if err := f.Sync(); err != nil {
+			log.Fatal(err)
+		}
+	}
+	var a int
+	_ = a
+}
+
 func deferredCloseWithSyncEarlyReturn(n int) {
 	// open file for writing
 	if f, err := os.OpenFile("foo.txt", os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0666); err != nil { // $ Source