4 files changed, 87 insertions, 0 deletions
diff --git a/src/tools/tidy/Cargo.toml b/src/tools/tidy/Cargo.toml
index 63963b0bd1c..f39438bd9ac 100644
--- a/src/tools/tidy/Cargo.toml
+++ b/src/tools/tidy/Cargo.toml
@@ -13,6 +13,7 @@ ignore = "0.4.18"
 semver = "1.0"
 termcolor = "1.1.3"
 rustc-hash = "1.1.0"
+fluent-syntax = "0.11.1"
 
 [[bin]]
 name = "rust-tidy"
diff --git a/src/tools/tidy/src/fluent_period.rs b/src/tools/tidy/src/fluent_period.rs
new file mode 100644
index 00000000000..3a1fb6daf48
--- /dev/null
+++ b/src/tools/tidy/src/fluent_period.rs
@@ -0,0 +1,84 @@
+//! Checks that no Fluent messages or attributes end in periods (except ellipses)
+
+use fluent_syntax::ast::{Entry, PatternElement};
+
+use crate::walk::{filter_dirs, walk};
+use std::path::Path;
+
+fn filter_fluent(path: &Path) -> bool {
+    if let Some(ext) = path.extension() { ext.to_str() != Some("ftl") } else { true }
+}
+
+/// Messages allowed to have `.` at their end.
+///
+/// These should probably be reworked eventually.
+const ALLOWLIST: &[&str] = &[
+    "const_eval_long_running",
+    "const_eval_validation_failure_note",
+    "driver_impl_ice",
+    "incremental_corrupt_file",
+    "mir_build_pointer_pattern",
+];
+
+fn check_period(filename: &str, contents: &str, bad: &mut bool) {
+    if filename.contains("codegen") {
+        // FIXME: Too many codegen messages have periods right now...
+        return;
+    }
+
+    let (Ok(parse) | Err((parse, _))) = fluent_syntax::parser::parse(contents);
+    for entry in &parse.body {
+        if let Entry::Message(m) = entry {
+            if ALLOWLIST.contains(&m.id.name) {
+                continue;
+            }
+
+            if let Some(pat) = &m.value {
+                if let Some(PatternElement::TextElement { value }) = pat.elements.last() {
+                    // We don't care about ellipses.
+                    if value.ends_with(".") && !value.ends_with("...") {
+                        let ll = find_line(contents, *value);
+                        let name = m.id.name;
+                        tidy_error!(bad, "{filename}:{ll}: message `{name}` ends in a period");
+                    }
+                }
+            }
+
+            for attr in &m.attributes {
+                // Teach notes usually have long messages.
+                if attr.id.name == "teach_note" {
+                    continue;
+                }
+
+                if let Some(PatternElement::TextElement { value }) = attr.value.elements.last() {
+                    if value.ends_with(".") && !value.ends_with("...") {
+                        let ll = find_line(contents, *value);
+                        let name = attr.id.name;
+                        tidy_error!(bad, "{filename}:{ll}: attr `{name}` ends in a period");
+                    }
+                }
+            }
+        }
+    }
+}
+
+/// Evil cursed bad hack. Requires that `value` be a substr (in memory) of `contents`.
+fn find_line(haystack: &str, needle: &str) -> usize {
+    for (ll, line) in haystack.lines().enumerate() {
+        if line.as_ptr() > needle.as_ptr() {
+            return ll;
+        }
+    }
+
+    1
+}
+
+pub fn check(path: &Path, bad: &mut bool) {
+    walk(
+        path,
+        |path, is_dir| filter_dirs(path) || (!is_dir && filter_fluent(path)),
+        &mut |ent, contents| {
+            check_period(ent.path().to_str().unwrap(), contents, bad);
+        },
+    );
+}
diff --git a/src/tools/tidy/src/lib.rs b/src/tools/tidy/src/lib.rs
index ae9d2b8b8dc..ecd32727fa0 100644
--- a/src/tools/tidy/src/lib.rs
+++ b/src/tools/tidy/src/lib.rs
@@ -72,6 +72,7 @@ pub mod ext_tool_checks;
 pub mod extdeps;
 pub mod features;
 pub mod fluent_alphabetical;
+pub mod fluent_period;
 mod fluent_used;
 pub(crate) mod iter_header;
 pub mod known_bug;
diff --git a/src/tools/tidy/src/main.rs b/src/tools/tidy/src/main.rs
index 1d2b2e4d034..ec6fc1f07f1 100644
--- a/src/tools/tidy/src/main.rs
+++ b/src/tools/tidy/src/main.rs
@@ -115,6 +115,7 @@ fn main() {
         // Checks that only make sense for the compiler.
         check!(error_codes, &root_path, &[&compiler_path, &librustdoc_path], verbose);
         check!(fluent_alphabetical, &compiler_path, bless);
+        check!(fluent_period, &compiler_path);
         check!(target_policy, &root_path);
 
         // Checks that only make sense for the std libs.