[ruff] Handle empty t-strings in unnecessary-empty-iterable-within-deque-call (RUF037) (astral-sh#20045)

Adds a method to `TStringValue` to detect whether the t-string is empty
_as an iterable_. Note the subtlety here that, unlike f-strings, an
empty t-string is still truthy (i.e. `bool(t"")==True`).

Closes astral-sh#19951

Author: dylwil3

crates/ruff_linter/resources/test/fixtures/ruff/RUF037.py

@@ -102,3 +102,8 @@ def f():
 deque(b"abc") # OK
 deque(f"" "a")  # OK
 deque(f"{x}" "")  # OK
+
+# https://github.com/astral-sh/ruff/issues/19951
+deque(t"")
+deque(t""  t"")
+deque(t"{""}") # OK

crates/ruff_linter/src/rules/ruff/rules/unnecessary_literal_within_deque_call.rs

@@ -103,6 +103,7 @@ pub(crate) fn unnecessary_literal_within_deque_call(checker: &Checker, deque: &a
         Expr::StringLiteral(string) => string.value.is_empty(),
         Expr::BytesLiteral(bytes) => bytes.value.is_empty(),
         Expr::FString(fstring) => fstring.value.is_empty_literal(),
+        Expr::TString(tstring) => tstring.value.is_empty_iterable(),
         _ => false,
     };
     if !is_empty_literal {

crates/ruff_linter/src/rules/ruff/snapshots/ruff_linter__rules__ruff__tests__RUF037_RUF037.py.snap

@@ -383,3 +383,42 @@ help: Replace with `deque()`
 101 101 | deque("abc") # OK
 102 102 | deque(b"abc") # OK
 103 103 | deque(f"" "a")  # OK
+
+RUF037 [*] Unnecessary empty iterable within a deque call
+   --> RUF037.py:107:1
+    |
+106 | # https://github.com/astral-sh/ruff/issues/19951
+107 | deque(t"")
+    | ^^^^^^^^^^
+108 | deque(t""  t"")
+109 | deque(t"{""}") # OK
+    |
+help: Replace with `deque()`
+
+ℹ Safe fix
+104 104 | deque(f"{x}" "")  # OK
+105 105 | 
+106 106 | # https://github.com/astral-sh/ruff/issues/19951
+107     |-deque(t"")
+    107 |+deque()
+108 108 | deque(t""  t"")
+109 109 | deque(t"{""}") # OK
+
+RUF037 [*] Unnecessary empty iterable within a deque call
+   --> RUF037.py:108:1
+    |
+106 | # https://github.com/astral-sh/ruff/issues/19951
+107 | deque(t"")
+108 | deque(t""  t"")
+    | ^^^^^^^^^^^^^^^
+109 | deque(t"{""}") # OK
+    |
+help: Replace with `deque()`
+
+ℹ Safe fix
+105 105 | 
+106 106 | # https://github.com/astral-sh/ruff/issues/19951
+107 107 | deque(t"")
+108     |-deque(t""  t"")
+    108 |+deque()
+109 109 | deque(t"{""}") # OK

crates/ruff_python_ast/src/nodes.rs

@@ -515,7 +515,7 @@ impl FStringValue {
 
     /// Returns `true` if the node represents an empty f-string literal.
     ///
-    /// Noteh that a [`FStringValue`] node will always have >= 1 [`FStringPart`]s inside it.
+    /// Note that a [`FStringValue`] node will always have >= 1 [`FStringPart`]s inside it.
     /// This method checks whether the value of the concatenated parts is equal to the empty
     /// f-string, not whether the f-string has 0 parts inside it.
     pub fn is_empty_literal(&self) -> bool {
@@ -681,6 +681,22 @@ impl TStringValue {
     pub fn elements(&self) -> impl Iterator<Item = &InterpolatedStringElement> {
         self.iter().flat_map(|tstring| tstring.elements.iter())
     }
+
+    /// Returns `true` if the node represents an empty t-string in the
+    /// sense that `__iter__` returns an empty iterable.
+    ///
+    /// Beware that empty t-strings are still truthy, i.e. `bool(t"") == True`.
+    ///
+    /// Note that a [`TStringValue`] node will always contain at least one
+    /// [`TString`] node. This method checks whether each of the constituent
+    /// t-strings (in an implicitly concatenated t-string) are empty
+    /// in the above sense.
+    pub fn is_empty_iterable(&self) -> bool {
+        match &self.inner {
+            TStringValueInner::Single(tstring) => tstring.is_empty(),
+            TStringValueInner::Concatenated(tstrings) => tstrings.iter().all(TString::is_empty),
+        }
+    }
 }
 
 impl<'a> IntoIterator for &'a TStringValue {
@@ -1182,6 +1198,10 @@ impl TString {
     pub fn quote_style(&self) -> Quote {
         self.flags.quote_style()
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.elements.is_empty()
+    }
 }
 
 impl From<TString> for Expr {