test-float-parse: Use an overrideable random seed

Cargo.toml

@@ -77,7 +77,8 @@ strip = true
 debug = 0
 strip = true
 
-# Bigint libraries are slow without optimization, speed up testing
+# Bigint libraries are slow without optimization, speed up testing. Note that this doesn't affect
+# its dependencies, it should still be run in release mode where possible.
 [profile.dev.package.test-float-parse]
 opt-level = 3
 
@@ -92,4 +93,3 @@ codegen-units = 1
 # If you want to use a crate with local modifications, you can set a path or git dependency here.
 # For git dependencies, also add your source to ALLOWED_SOURCES in src/tools/tidy/src/extdeps.rs.
 #[patch.crates-io]
-

src/tools/test-float-parse/Cargo.toml

@@ -5,11 +5,12 @@ edition = "2024"
 publish = false
 
 [dependencies]
-indicatif = { version = "0.17.8", default-features = false }
+base64 = "0.22.1"
+indicatif = { version = "0.18.3", default-features = false }
 num = "0.4.3"
-rand = "0.9.0"
-rand_chacha = "0.9.0"
-rayon = "1"
+rand = "0.10.0"
+rand_chacha = "0.10.0"
+rayon = "1.11.0"
 
 [lib]
 name = "test_float_parse"

src/tools/test-float-parse/build.rs

@@ -0,0 +1,9 @@
+use std::env;
+
+fn main() {
+    // Forward the opt level so we can warn if the tests are going to be slow.
+    let opt = env::var("OPT_LEVEL").expect("OPT_LEVEL unset");
+    let profile = env::var("PROFILE").expect("PROFILE unset");
+    println!("cargo::rustc-env=OPT_LEVEL={opt}");
+    println!("cargo::rustc-env=PROFILE={profile}");
+}

src/tools/test-float-parse/src/gen_/fuzz.rs

@@ -5,7 +5,7 @@ use std::marker::PhantomData;
 use std::ops::Range;
 use std::sync::Mutex;
 
-use rand::Rng;
+use rand::RngExt;
 use rand::distr::{Distribution, StandardUniform};
 use rand_chacha::ChaCha8Rng;
 use rand_chacha::rand_core::SeedableRng;
@@ -62,7 +62,7 @@ where
     }
 
     fn new() -> Self {
-        let rng = ChaCha8Rng::from_seed(SEED);
+        let rng = ChaCha8Rng::from_seed(SEED.0);
 
         Self { iter: 0..Self::total_tests(), rng, marker: PhantomData }
     }

src/tools/test-float-parse/src/gen_/many_digits.rs

@@ -4,7 +4,7 @@ use std::marker::PhantomData;
 use std::ops::{Range, RangeInclusive};
 
 use rand::distr::{Distribution, Uniform};
-use rand::{Rng, SeedableRng};
+use rand::{RngExt, SeedableRng};
 use rand_chacha::ChaCha8Rng;
 
 use crate::{Float, Generator, SEED};
@@ -39,7 +39,7 @@ impl<F: Float> Generator<F> for RandDigits<F> {
     }
 
     fn new() -> Self {
-        let rng = ChaCha8Rng::from_seed(SEED);
+        let rng = ChaCha8Rng::from_seed(SEED.0);
         let range = Uniform::try_from(0..10).unwrap();
 
         Self { rng, iter: 0..ITERATIONS, uniform: range, marker: PhantomData }

src/tools/test-float-parse/src/lib.rs

@@ -10,11 +10,15 @@ use std::any::type_name;
 use std::cmp::min;
 use std::ops::RangeInclusive;
 use std::process::ExitCode;
-use std::sync::OnceLock;
 use std::sync::atomic::{AtomicU64, Ordering};
-use std::{fmt, time};
+use std::sync::{LazyLock, OnceLock};
+use std::{env, fmt, time};
 
+use base64::engine::Engine;
+use base64::engine::general_purpose::URL_SAFE_NO_PAD;
+use rand::TryRng;
 use rand::distr::{Distribution, StandardUniform};
+use rand::rngs::SysRng;
 use rayon::prelude::*;
 use time::{Duration, Instant};
 use traits::{Float, Generator, Int};
@@ -44,8 +48,26 @@ const MAX_BITS_FOR_EXHAUUSTIVE: u32 = 32;
 /// `--skip-huge`.
 const HUGE_TEST_CUTOFF: u64 = 5_000_000;
 
-/// Seed for tests that use a deterministic RNG.
-const SEED: [u8; 32] = *b"3.141592653589793238462643383279";
+const SEED_ENV: &str = "TEST_FLOAT_PARSE_SEED";
+
+/// Seed for tests that use a deterministic RNG, and its b64 representation for printing. Taken
+/// from env if provided,
+static SEED: LazyLock<([u8; 32], Box<str>)> = LazyLock::new(|| {
+    let seed = match env::var(SEED_ENV) {
+        Ok(s) => URL_SAFE_NO_PAD
+            .decode(s)
+            .ok()
+            .and_then(|decoded| <[u8; 32]>::try_from(decoded).ok())
+            .unwrap_or_else(|| panic!("{SEED_ENV} must be 32 bytes, base64 encoded")),
+        Err(_) => {
+            let mut seed = [0u8; 32];
+            SysRng.try_fill_bytes(&mut seed).unwrap();
+            seed
+        }
+    };
+    let encoded = URL_SAFE_NO_PAD.encode(&seed).into_boxed_str();
+    (seed, encoded)
+});
 
 /// Global configuration.
 #[derive(Debug)]
@@ -78,8 +100,10 @@ pub fn run(cfg: Config, include: &[String], exclude: &[String]) -> ExitCode {
     let threads = std::thread::available_parallelism().map(Into::into).unwrap_or(0) * 3 / 2;
     rayon::ThreadPoolBuilder::new().num_threads(threads).build_global().unwrap();
 
+    println!("Starting test runner");
+    println!("Using {SEED_ENV}={}`", SEED.1);
     let mut tests = register_tests(&cfg);
-    println!("registered");
+    println!("Tests registered");
     let initial_tests: Vec<_> = tests.iter().map(|t| t.name.clone()).collect();
 
     let unmatched: Vec<_> = include

src/tools/test-float-parse/src/main.rs

@@ -39,12 +39,24 @@ enum ArgMode {
 }
 
 fn main() -> ExitCode {
-    if cfg!(debug_assertions) {
+    let opt = env!("OPT_LEVEL");
+    let profile = env!("PROFILE");
+
+    println!("Crate config:");
+    println!("    opt level: {opt}");
+    println!("    profile: {profile}");
+    println!("    debug assertions: {}", cfg!(debug_assertions));
+
+    if !matches!(opt, "2" | "3") || profile != "release" {
+        // Warn for `profile != release` because optimizations being on for this crate (always,
+        // via the workspace Cargo.toml)  may not mean they are on for dependencies.
         println!(
-            "WARNING: running in debug mode. Release mode is recommended to reduce test duration."
+            "WARNING: test-float-parse may be running unoptimized or with unoptimized \
+            dependencies. Release mode is recommended to reduce test duration."
         );
         std::thread::sleep(Duration::from_secs(2));
     }
+    println!("Running with debug assertions={}", cfg!(debug_assertions));
 
     let args: Vec<_> = std::env::args().skip(1).collect();
     if args.iter().any(|arg| arg == "--help" || arg == "-h") {

src/tools/test-float-parse/src/ui.rs

@@ -8,7 +8,7 @@ use std::time::Duration;
 
 use indicatif::{ProgressBar, ProgressStyle};
 
-use crate::{Completed, Config, EarlyExit, FinishedAll, TestInfo};
+use crate::{Completed, Config, EarlyExit, FinishedAll, SEED, SEED_ENV, TestInfo};
 
 /// Templates for progress bars.
 const PB_TEMPLATE: &str = "[{elapsed:3} {percent:3}%] {bar:20.cyan/blue} NAME \
@@ -135,6 +135,16 @@ pub fn finish_all(tests: &[TestInfo], total_elapsed: Duration, cfg: &Config) ->
     );
 
     if failed_generators > 0 || stopped_generators > 0 {
+        println!();
+        println!(
+            "ERROR: Some float parsing/printing tests failed.\n\
+            \n\
+            If you ever encounter this failure when not expected, PLEASE OPEN AN ISSUE!! The \
+            failure will likely go away on the next run, but may represent a real bug.\n\
+            \n\
+            To reproduce, rerun with the same seed: {}={}",
+            SEED_ENV, SEED.1
+        );
         ExitCode::FAILURE
     } else {
         ExitCode::SUCCESS