Prevent inline snapshots in loops. Fixes #307

CHANGELOG.md

@@ -7,6 +7,7 @@ All notable changes to insta and cargo-insta are documented here.
 - Added support for rendering some invisibles in diffs.  This now also
   should make sure that ANSI sequences in strings are no longer screwing
   up the terminal output. (#308)
+- Prevent inline snapshots to be used in loops. (#307)
 
 ## 1.21.2
 

src/runtime.rs

@@ -1,5 +1,5 @@
 use std::borrow::Cow;
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, BTreeSet};
 use std::error::Error;
 use std::fs;
 use std::io::Write;
@@ -21,6 +21,8 @@ lazy_static::lazy_static! {
         Mutex::new(BTreeMap::new());
     static ref TEST_NAME_CLASH_DETECTION: Mutex<BTreeMap<String, bool>> =
         Mutex::new(BTreeMap::new());
+    static ref INLINE_DUPLICATES: Mutex<BTreeSet<String>> =
+        Mutex::new(BTreeSet::new());
 }
 
 // This macro is basically eprintln but without being captured and
@@ -243,6 +245,7 @@ impl<'a> SnapshotAssertionContext<'a> {
                 snapshot_file = Some(file);
             }
             ReferenceValue::Inline(contents) => {
+                prevent_inline_duplicate(function_name, assertion_file, assertion_line);
                 snapshot_name = detect_snapshot_name(function_name, module_path, true, is_doctest)
                     .ok()
                     .map(Cow::Owned);
@@ -411,6 +414,17 @@ impl<'a> SnapshotAssertionContext<'a> {
     }
 }
 
+fn prevent_inline_duplicate(function_name: &str, assertion_file: &str, assertion_line: u32) {
+    let key = format!("{}|{}|{}", function_name, assertion_file, assertion_line);
+    let mut set = INLINE_DUPLICATES.lock().unwrap();
+    if set.contains(&key) {
+        // drop the lock so we don't poison it
+        drop(set);
+        panic!("Insta does not allow inline snapshot assertions in loops");
+    }
+    set.insert(key);
+}
+
 /// This prints the information about the snapshot
 fn print_snapshot_info(ctx: &SnapshotAssertionContext, new_snapshot: &Snapshot) {
     match get_output_behavior() {

tests/test_inline.rs

@@ -278,3 +278,11 @@ fn test_compact_json() {
     ]
     "###);
 }
+
+#[test]
+#[should_panic = "Insta does not allow inline snapshot assertions in loops"]
+fn test_inline_test_in_loop() {
+    for i in 0..10 {
+        assert_snapshot!(i.to_string(), @"0");
+    }
+}