[llvm] [clang] [clang][DependencyScanner] Remove unused -ivfsoverlay files (PR #73734)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

We set `RedirectingFileSystem::HasBeenUsed` to `true` while implicitly compiling one module, but then hand off the same VFS object to implicit compile of another module. This will cause all modules discovered later to incorrectly inherit that bit from previous modules. This will also introduce non-determinism based on the TU that reached a module first (and which modules it imported on the way). Here's a test case:
```
// This test checks that VFS usage doesn't leak between modules.

// RUN: rm -rf %t && split-file %s %t
// RUN: sed -e "s|DIR|%/t|g" %t/build/cdb.json.in > %t/build/cdb.json
// RUN: sed -e "s|DIR|%/t|g" %t/build/vfs.yaml.in > %t/build/vfs.yaml
// RUN: clang-scan-deps -compilation-database %t/build/cdb.json \
// RUN:   -format experimental-full --optimize-args=vfs > %t/deps.json
// RUN: cat %t/deps.json | sed 's:\\\\\?:/:g' | FileCheck %s -DPREFIX=%/t

// CHECK:      {
// CHECK-NEXT:   "modules": [
// CHECK-NEXT:     {
// CHECK-NEXT:       "clang-module-deps": [
// CHECK-NEXT:         {
// CHECK-NEXT:           "context-hash": "{{.*}}",
// CHECK-NEXT:           "module-name": "B"
// CHECK-NEXT:         },
// CHECK-NEXT:         {
// CHECK-NEXT:           "context-hash": "{{.*}}",
// CHECK-NEXT:           "module-name": "C"
// CHECK-NEXT:         }
// CHECK-NEXT:       ],
// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/moduleA/module.modulemap",
// CHECK-NEXT:       "command-line": [
// Module A needs the VFS overlay because its dependency, module B, needs it.
// CHECK:              "-ivfsoverlay"
// CHECK-NEXT:         "[[PREFIX]]/build/vfs.yaml"
// CHECK:            ],
// CHECK-NEXT:       "context-hash": "{{.*}}",
// CHECK-NEXT:       "file-deps": [
// CHECK:            ],
// CHECK-NEXT:       "name": "A"
// CHECK-NEXT:     },
// CHECK-NEXT:     {
// CHECK-NEXT:       "clang-module-deps": [],
// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/moduleB/module.modulemap",
// CHECK-NEXT:       "command-line": [
// Module B needs the VFS overlay because it provides the header referred to by the module map.
// CHECK:              "-ivfsoverlay"
// CHECK-NEXT:         "[[PREFIX]]/build/vfs.yaml"
// CHECK:            ],
// CHECK-NEXT:       "context-hash": "{{.*}}",
// CHECK-NEXT:       "file-deps": [
// CHECK:            ],
// CHECK-NEXT:       "name": "B"
// CHECK-NEXT:     },
// CHECK-NEXT:     {
// CHECK-NEXT:       "clang-module-deps": [],
// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/moduleC/module.modulemap",
// CHECK-NEXT:       "command-line": [
// Module C doesn't need the VFS overlay.
// CHECK-NOT:          "-ivfsoverlay"
// CHECK:            ],
// CHECK-NEXT:       "context-hash": "{{.*}}",
// CHECK-NEXT:       "file-deps": [
// CHECK:            ],
// CHECK-NEXT:       "name": "C"
// CHECK-NEXT:     }
// CHECK-NEXT:   ],
// CHECK-NEXT:   "translation-units": [
// CHECK:        ]
// CHECK:      }

//--- build/cdb.json.in
[{
  "directory": "DIR",
  "command": "clang -c DIR/tu.m -I DIR/moduleA -I DIR/moduleB -I DIR/moduleC -fmodules -fmodules-cache-path=DIR/cache -fimplicit-module-maps -ivfsoverlay DIR/build/vfs.yaml",
  "file": "DIR/tu.m"
}]

//--- build/vfs.yaml.in
{
  "version": 0,
  "case-sensitive": "false",
  "roots": [
    {
      "contents": [
        {
          "external-contents": "DIR/build/B.h",
          "name": "B.h",
          "type": "file"
        }
      ],
      "name": "DIR/moduleB",
      "type": "directory"
    }
  ]
}

//--- tu.m
@import A;

//--- moduleA/module.modulemap
module A { header "A.h" }
//--- moduleA/A.h
@import B;
@import C;

//--- moduleB/module.modulemap
module B { header "B.h" }
//--- build/B.h

//--- moduleC/module.modulemap
module C { header "C.h" }
//--- moduleC/C.h
```

https://github.com/llvm/llvm-project/pull/73734