gopls/internal/golang: fix extract bug with anon functions

When the extracted block contains return statements but doesn't have
any non-nested returns, we adjust all return statements in the
extracted function. However, we need to avoid modifying the return statements
of anonymous functions since this would change function behavior or
cause a type error.

Fixes golang/go#73972

Change-Id: I6e5c145c844d29c9ceae32da341b99a1ff1b2d54
Reviewed-on: https://go-review.googlesource.com/c/tools/+/678915
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: madelinekalil

gopls/internal/golang/extract.go

@@ -1896,6 +1896,10 @@ func adjustReturnStatements(returnTypes []*ast.Field, seenVars map[types.Object]
 		if n == nil {
 			return false
 		}
+		// Don't modify return statements inside anonymous functions.
+		if _, ok := n.(*ast.FuncLit); ok {
+			return false
+		}
 		if n, ok := n.(*ast.ReturnStmt); ok {
 			n.Results = slices.Concat(zeroVals, n.Results)
 			return false

gopls/internal/test/marker/testdata/codeaction/functionextraction_issue73972.txt

@@ -0,0 +1,52 @@
+This test verifies the fix for golang/go#73972: extraction should
+not modify the return statements of anonymous functions.
+
+-- go.mod --
+module mod.test/extract
+
+go 1.18
+
+-- a.go --
+package extract
+
+import (
+    "fmt"
+    "strings"
+)
+
+func main() {
+	b := strings.ContainsFunc("a", func(_ rune) bool { //@codeaction("b", "refactor.extract.function", end=end, result=ext)
+		return false
+	})
+	if b {
+		return
+	} //@loc(end, "}")
+	fmt.Println(b)
+}
+
+-- @ext/a.go --
+package extract
+
+import (
+    "fmt"
+    "strings"
+)
+
+func main() {
+	b, shouldReturn := newFunction()
+	if shouldReturn {
+		return
+	} //@loc(end, "}")
+	fmt.Println(b)
+}
+
+func newFunction() (bool, bool) {
+	b := strings.ContainsFunc("a", func(_ rune) bool { //@codeaction("b", "refactor.extract.function", end=end, result=ext)
+		return false
+	})
+	if b {
+		return false, true
+	}
+	return b, false
+}
+