Very minimal error reporting on missing return type in external functions

[Blei]

The following program:

private external foo() {
    return 1;
}

main() {
    foo();
}

doesn't compile, which is expected. The displayed error message is maybe a bit too minimal though:

error: expected 0 values, but received 1 value

No backtrace, no mention of the problem being a missing return type declaration. It feels like this might actually be a compiler error and not a user facing error.

[Blei]

Something similar happens for non-external procedures (it displays an incorrect location: the call site instead of the return statement), which made me suspect that there was a missing pushLocation() call somewhere. And indeed, with this hacky little patch the error reporting is improved greatly.

diff --git a/compiler/codegen.cpp b/compiler/codegen.cpp
index 666c181..756cc46 100644
--- a/compiler/codegen.cpp
+++ b/compiler/codegen.cpp
@@ -3909,7 +3909,9 @@ bool codegenStatement(StatementPtr stmt,
         MultiPValuePtr mpv = safeAnalyzeMulti(x->values, env, 1);
         MultiCValuePtr mcv = new MultiCValue();
         llvm::ArrayRef<CReturn> returns = ctx->returnLists.back();
+        pushLocation(x->location);
         ensureArity(mpv, returns.size());
+        popLocation();
         for (unsigned i = 0; i < mpv->size(); ++i) {
             PVData const &pv = mpv->values[i];
             bool byRef = returnKindToByRef(x->returnKind, pv);

I'm sure there's a more correct location for this call though, so I won't submit this as a pull request.

[galchinsky]

the call site instead of the return statement

Then if you write foo(println("x"));, you'll get to library source and the compiler will tell you that "println misses return value". Weird. At least there should be 2 places (caller and called)

[Blei]

No, it won't. The error that is reported happens at the return statement, so it should show the return statement as the error location. Your example still works as before.