Hash sign in multiline string causes "Unknown preprocessor directive" error

[bbrk24]

Please include the following in your bug report:

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.32 (eab98adf462c39f3c31d348331c4830bcaa36949)
clang version 17.0.0 (https://github.com/llvm/llvm-project df82394e7a2d06506718cafa347bf7827c79fc4f)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: C:\[...]\emsdk\upstream\bin

Failing command line in full:

emcc ./*.cpp --post-js post.js 

Where post.js is:

const foo = `
#bar`;

Note that this does not happen if the hash sign is not the first (non-whitespace) character on the line. So, this would not trigger the error:

const foo = '\n#bar';

Full link command and output with -v appended:
Full output is over 26kB, so I can't attach it here. The wasm file is successfully generated, however. Without -v, the output is (with some paths redacted):

Internal compiler error in src/compiler.js!
Please create a bug report at https://github.com/emscripten-core/emscripten/issues/
with a log of the build and the input files used to run. Exception message: "Error: C:\[...]\[...]\post.js:2: Unknown preprocessor directive #bar`;
    at preprocess (C:\[...]\emsdk\upstream\emscripten\src\parseTools.js:137:17)
    at includeFile (C:\[...]\emsdk\upstream\emscripten\src\jsifier.js:456:25)
    at finalCombiner (C:\[...]\emsdk\upstream\emscripten\src\jsifier.js:528:7)
    at runJSify (C:\[...]\emsdk\upstream\emscripten\src\jsifier.js:552:3)
    at Object.<anonymous> (C:\[...]\emsdk\upstream\emscripten\src\compiler.js:97:3)
    at Module._compile (internal/modules/cjs/loader.js:1085:14)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)
    at Module.load (internal/modules/cjs/loader.js:950:32)
    at Function.Module._load (internal/modules/cjs/loader.js:790:12)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:76:12)
emcc: error: 'C:/[...]/emsdk/node/14.18.2_64bit/bin/node.exe C:\[...]\emsdk\upstream\emscripten\src\compiler.js 
C:\[...]\AppData\Local\Temp\tmppyhfuv98.json' failed (returned 1)

[sbc100]

I believe this is a duplicate of #18609.

[bbrk24]

It does seem to be the same general issue, but they could be considered distinct: that one found it in a block comment, while I encountered it in a multiline string.