Bug: No matching configuration found warning for code block matched only by non-universal patterns

[mdjermanovic]

Environment

Node version: v20.12.0
npm version: 10.5.0
Local ESLint version: v9.3.0
Global ESLint version: no
Operating System: windows

What parser are you using?

Default (Espree)

What did you do?

I wanted to make a repro with eslint-plugin-markdown, but since this warning has line: 0 (which might be another bug), eslint-plugin-markdown filters it out as out-of-range. So I made a simple processor that assumes that the entire markdown file is one ```ts code block.

// eslint.config.js
export default [
  {
      plugins: {
          "my-plugin": {
              processors: {
                  "my-processor": {

                      // dummy processor that assumes that the whole content of a file is a single ```ts code block 
                      preprocess(text) {
                          const lines = text.split("\n");
                          return [{
                              filename: "foo.ts",
                              text: lines.slice(1, -1).join("\n")
                          }]
                      },

                      // just increment lines to adjust for the first ```ts line
                      postprocess(messages) {
                          const retv = messages[0]; // there's always exactly 1 code block

                          retv.forEach(message => {
                              message.line++
                              message.endLine++; 
                          });

                          return retv;
                      }
                  }
              }
          }
      }
  },
  {
      files: ["**/*.md"],
      processor: "my-plugin/my-processor"
  },
  {
      files: ["**/*"],
      rules: {
          "no-undef": 2
      }
  }
];

test.md:

```ts
foo
```

What did you expect to happen?

Since the .ts virtual file doesn't have an explicit match in the config, I'd expect it to be silently ignored, so at the end I'd expect no lint errors or warnings.

What actually happened?

C:\projects\tmp\tmp\test.md
  1:0  warning  No matching configuration found for C:\projects\tmp\tmp\test.md\0_foo.ts

✖ 1 problem (0 errors, 1 warning)

Link to Minimal Reproducible Example

https://stackblitz.com/edit/stackblitz-starters-hqxgng?file=eslint.config.js

Participation

• I am willing to submit a pull request for this issue.

Additional comments

We found this problem while discussing eslint/rewrite#7.

I think we could just replace the following line with return configs.getConfig(blockFilename) !== void 0;

eslint/lib/eslint/eslint.js

Line 512 in 389744b

return configs.isExplicitMatch(blockFilename);

[fasttime]

Thanks for the issue and the repro. Marked as accepted.

[mdjermanovic]

I'm working on this.