Support AST parsing with -trimpath flag

Checking the trimmed path to see if some suffix is a valid filepath is
probably not a perfect system, but it should be able to work at least
some of the time, which is better than nothing.

.github/workflows/go.yml

@@ -11,13 +11,16 @@ permissions:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
     strategy:
       matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
         go-version:
           - '1.19'
           - '1.20'
           - '1.21'
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
       - name: Set up Go ${{ matrix.go-version }}
@@ -28,6 +31,8 @@ jobs:
         run: go build -v ./...
       - name: Test
         run: go test -v ./...
+      - name: Test -trimpath
+        run: go test -trimpath -v ./...
 
   lint:
     runs-on: ubuntu-latest

ghostlib/ast.go

@@ -8,6 +8,7 @@ import (
 	"go/format"
 	"go/parser"
 	"go/token"
+	"os"
 	"runtime"
 	"strings"
 )
@@ -54,6 +55,8 @@ func callExprArgs(skip int) ([]ast.Expr, error) {
 		return nil, errors.New("failed to get file/line")
 	}
 
+	filename = findSystemFilepath(filename)
+
 	wantFunc := runtime.FuncForPC(pc)
 
 	fset := token.NewFileSet()
@@ -70,6 +73,30 @@ func callExprArgs(skip int) ([]ast.Expr, error) {
 	return node.Args, nil
 }
 
+// Passing the -trimpath flag will prevent looking up filepaths directly.
+// In most cases, some suffix of the path will be a valid relative path, which
+// we can use instead.
+func findSystemFilepath(filename string) string {
+	if _, err := os.Stat(filename); err == nil {
+		return filename
+	}
+
+	cur := filename
+	for {
+		parts := strings.SplitN(cur, "/", 2)
+		if len(parts) < 2 {
+			break
+		}
+
+		cur = parts[1]
+		if _, err := os.Stat(cur); err == nil {
+			return cur
+		}
+	}
+
+	return filename
+}
+
 func callExprForFunc(
 	wantFunc *runtime.Func,
 	fset *token.FileSet,