tsconfig include silently drops Foo.tsx when foo.ts exists, on a case-insensitive filesystem #64098

🔎 Search Terms

include, wildcard, extension priority, case-insensitive file system, hasFileWithHigherPriorityExtension, .ts vs .tsx, file silently excluded from program

🕗 Version & Regression Information

Reproduces on 6.0.3 and on 7.0.2 (native). This is long-standing behaviour, not a recent regression — I did not bisect it.

⏯ Playground Link

Not applicable: the bug is in tsconfig file selection, so it needs two files on disk.

💻 Code

Three files, no dependencies:

src/brand.ts

export const brand = "ok";

src/Brand.tsx — note the capital B

// A deliberate type error. If this file is in the program, tsc MUST report it.
export const oops: number = "not a number";

tsconfig.json

{
  "compilerOptions": { "noEmit": true, "strict": true, "jsx": "react-jsx", "types": [] },
  "include": ["src/**/*"]
}

Run tsc --showConfig -p tsconfig.json and tsc --noEmit -p tsconfig.json.

One-liner for the Linux side, if you are on a Mac:

docker run --rm -v "$PWD":/src:ro -w /app oven/bun:latest \
  sh -c 'cp -a /src/. /app/ && bun add typescript@7.0.2 >/dev/null 2>&1 && \
         ./node_modules/.bin/tsc --noEmit -p tsconfig.json'

🙁 Actual behavior

On a case-insensitive filesystem (macOS APFS, and Windows), src/Brand.tsx is dropped from the program with no diagnostic at all:

$ tsc --showConfig -p tsconfig.json
    "files": [
        "./src/brand.ts"
    ],
$ tsc --noEmit -p tsconfig.json
$ echo $?
0

On a case-sensitive filesystem, the same tree, same compiler, same tsconfig:

$ tsc --showConfig -p tsconfig.json
    "files": [
        "./src/Brand.tsx",
        "./src/brand.ts"
    ],
$ tsc --noEmit -p tsconfig.json
src/Brand.tsx(2,14): error TS2322: Type 'string' is not assignable to type 'number'.
$ echo $?      # 2 on 6.0.3, 1 on 7.0.2

Verified identical on 6.0.3 (JS) and 7.0.2 (native) — both compilers, both directions.

🙂 Expected behavior

src/brand.ts and src/Brand.tsx are two different files with two different names. The .ts > .tsx > .d.ts de-duplication is meant for files that differ only in extension (foo.ts vs foo.tsx), and it should not fire across a base-name case difference.

If the de-dup is intentional here, it should at least not be silent. Today a file simply vanishes from the build: tsc exits 0 and prints nothing, so nothing tells the author their source was never compiled.

Cause

getFileNames in src/compiler/commandLineParser.ts (TS 7: internal/tsoptions/tsconfigparsing.go) calls:

if (hasFileWithHigherPriorityExtension(file, literalFileMap, wildcardFileMap, supportedExtensions, keyMapper)) {
  continue;
}

and hasFileWithHigherPriorityExtension does:

const higherPriorityPath = keyMapper(changeExtension(file, ext));
if (literalFiles.has(higherPriorityPath) || wildcardFiles.has(higherPriorityPath)) {
  ...
  return true;
}

keyMapper is createGetCanonicalFileName(host.useCaseSensitiveFileNames), which case-folds on a case-insensitive host. So for file = /p/src/Brand.tsx and ext = ".ts":

changeExtension → /p/src/Brand.ts → keyMapper → /p/src/brand.ts

which is already in wildcardFileMap (from the real src/brand.ts), so Brand.tsx is skipped. The extension key is case-folded together with the base name, and the base name is what actually differs.

Notes

• The file is not unresolvable on macOS. Adding import "./Brand.tsx" from another file in the program pulls it in and the error appears immediately. Only the include wildcard refuses it.
• forceConsistentCasingInFileNames does not help: there is no import to check the casing of. The file at issue here is a bundler entry point with no importer in the TS program, which is exactly the shape that hides this.
• Listing the file explicitly in "files" also works around it (literalFileMap is populated before the wildcard pass).

Why this hurt

A repo of mine had packages/templates/src/Brand.tsx (a Remotion render entry) sitting next to packages/templates/src/brand.ts (its config module). The .tsx had a real type error and had never been compiled on any developer machine — every local tsc was green. CI runs on Linux, where it was red. Because the file itself looked fine and the tooling versions were pinned and identical, the divergence got misdiagnosed for a full session as a generic-inference difference in a third-party library's .d.ts, and "fixed" by adding as unknown as casts to silence it. The actual bug was that half the team's compiler had never read the file.