argv[0] is not accessible to Lean

[eric-wieser]

Prerequisites

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• Reduce the issue to a minimal, self-contained, reproducible test case.
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Description

The lean def main is passed arg[1] to argv[argc - 1].

This is consistent with the behavior of Haskell's getArgs, but Lean does not provide haskell's getProgName.

IO.appPath is not a substitute for argv[0], as:

• argv[0] contains the pre-resolved symlinks
• The caller of exec can override argv[0] arbitrarily.

Context

Zulip thread

Steps to Reproduce

1. Create a lean binary foo
2. Run (exec -a secret_name ./lake/build/bin/foo)

Expected behavior: secret_name should either be in the first entry of args, or accessible via some IO API

Actual behavior: secret_name is lost forever:

lean4/src/Lean/Compiler/IR/EmitC.lean

Lines 173 to 182 in 01d414a

	if xs.size == 2 then
	emitLns ["in = lean_box(0);",
	"int i = argc;",
	"while (i > 1) {",
	" lean_object* n;",
	" i--;",
	" n = lean_alloc_ctor(1,2,0); lean_ctor_set(n, 0, lean_mk_string(argv[i])); lean_ctor_set(n, 1, in);",
	" in = n;",
	"}"]
	emitLn ("res = " ++ leanMainFn ++ "(in, lean_io_mk_world());")

Versions

[Output of #eval Lean.versionString]
[OS version, if not using live.lean-lang.org.]

Additional Information

[Additional information, configuration or data that might be necessary to reproduce the issue]

Impact

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