migrate fmt-write-bloat to rmake

src/tools/run-make-support/src/env.rs

@@ -17,3 +17,10 @@ pub fn env_var_os(name: &str) -> OsString {
         None => panic!("failed to retrieve environment variable {name:?}"),
     }
 }
+
+/// Check if `NO_DEBUG_ASSERTIONS` is set (usually this may be set in CI jobs).
+#[track_caller]
+#[must_use]
+pub fn no_debug_assertions() -> bool {
+    std::env::var_os("NO_DEBUG_ASSERTIONS").is_some()
+}

src/tools/run-make-support/src/lib.rs

@@ -21,6 +21,7 @@ pub mod run;
 pub mod scoped_run;
 pub mod string;
 pub mod targets;
+pub mod symbols;
 
 // Internally we call our fs-related support module as `fs`, but re-export its content as `rfs`
 // to tests to avoid colliding with commonly used `use std::fs;`.

src/tools/run-make-support/src/symbols.rs

@@ -0,0 +1,44 @@
+use std::path::Path;
+
+use object::{self, Object, ObjectSymbol, SymbolIterator};
+
+/// Iterate through the symbols in an object file.
+///
+/// Uses a callback because `SymbolIterator` does not own its data.
+///
+/// Panics if `path` is not a valid object file readable by the current user.
+pub fn with_symbol_iter<P, F, R>(path: P, func: F) -> R
+where
+    P: AsRef<Path>,
+    F: FnOnce(&mut SymbolIterator<'_, '_>) -> R,
+{
+    let raw_bytes = crate::fs::read(path);
+    let f = object::File::parse(raw_bytes.as_slice()).expect("unable to parse file");
+    let mut iter = f.symbols();
+    func(&mut iter)
+}
+
+/// Check an object file's symbols for substrings.
+///
+/// Returns `true` if any of the symbols found in the object file at
+/// `path` contain a substring listed in `substrings`.
+///
+/// Panics if `path` is not a valid object file readable by the current user.
+pub fn any_symbol_contains(path: impl AsRef<Path>, substrings: &[&str]) -> bool {
+    with_symbol_iter(path, |syms| {
+        for sym in syms {
+            for substring in substrings {
+                if sym
+                    .name_bytes()
+                    .unwrap()
+                    .windows(substring.len())
+                    .any(|x| x == substring.as_bytes())
+                {
+                    eprintln!("{:?} contains {}", sym, substring);
+                    return true;
+                }
+            }
+        }
+        false
+    })
+}

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -10,7 +10,6 @@ run-make/dep-info-spaces/Makefile
 run-make/dep-info/Makefile
 run-make/emit-to-stdout/Makefile
 run-make/extern-fn-reachable/Makefile
-run-make/fmt-write-bloat/Makefile
 run-make/foreign-double-unwind/Makefile
 run-make/foreign-exceptions/Makefile
 run-make/incr-add-rust-src-component/Makefile

tests/run-make/fmt-write-bloat/rmake.rs

@@ -0,0 +1,37 @@
+//! Before #78122, writing any `fmt::Arguments` would trigger the inclusion of `usize` formatting
+//! and padding code in the resulting binary, because indexing used in `fmt::write` would generate
+//! code using `panic_bounds_check`, which prints the index and length.
+//!
+//! These bounds checks are not necessary, as `fmt::Arguments` never contains any out-of-bounds
+//! indexes. The test is a `run-make` test, because it needs to check the result after linking. A
+//! codegen or assembly test doesn't check the parts that will be pulled in from `core` by the
+//! linker.
+//!
+//! In this test, we try to check that the `usize` formatting and padding code are not present in
+//! the final binary by checking that panic symbols such as `panic_bounds_check` are **not**
+//! present.
+//!
+//! Some CI jobs try to run faster by disabling debug assertions (through setting
+//! `NO_DEBUG_ASSERTIONS=1`). If debug assertions are disabled, then we can check for the absence of
+//! additional `usize` formatting and padding related symbols.
+
+// Reason: This test is `ignore-windows` because the `no_std` test (using `#[link(name = "c")])`
+// doesn't link on windows.
+//@ ignore-windows
+//@ ignore-cross-compile
+
+use run_make_support::env::no_debug_assertions;
+use run_make_support::rustc;
+use run_make_support::symbols::any_symbol_contains;
+
+fn main() {
+    rustc().input("main.rs").opt().run();
+    // panic machinery identifiers, these should not appear in the final binary
+    let mut panic_syms = vec!["panic_bounds_check", "Debug"];
+    if no_debug_assertions() {
+        // if debug assertions are allowed, we need to allow these,
+        // otherwise, add them to the list of symbols to deny.
+        panic_syms.extend_from_slice(&["panicking", "panic_fmt", "pad_integral", "Display"]);
+    }
+    assert!(!any_symbol_contains("main", &panic_syms));
+}