fix(noUselessEscapeInString): correctly flag chars (#9420)

Author: ematipico

.changeset/fix-css-unicode-escape-in-string.md

@@ -0,0 +1,5 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#9385](https://github.com/biomejs/biome/issues/9385): [`noUselessEscapeInString`](https://biomejs.dev/linter/rules/no-useless-escape-in-string/) no longer incorrectly flags valid CSS hex escapes (e.g. `\e7bb`) as useless. The rule now recognizes all hex digits (`0-9`, `a-f`, `A-F`) as valid escape characters in CSS strings.

crates/biome_css_analyze/src/lint/suspicious/no_useless_escape_in_string.rs

@@ -19,7 +19,7 @@ declare_lint_rule! {
     ///
     /// ```css,expect_diagnostic
     /// a::after {
-    ///   content: "\a"
+    ///   content: "\z"
     /// }
     /// ```
     ///
@@ -43,6 +43,12 @@ declare_lint_rule! {
     /// }
     /// ```
     ///
+    /// ```css
+    /// a::after {
+    ///   content: "\e7bb"
+    /// }
+    /// ```
+    ///
     pub NoUselessEscapeInString {
         version: "2.0.0",
         name: "noUselessEscapeInString",
@@ -109,10 +115,10 @@ fn next_useless_escape(str: &str, quote: u8) -> Option<usize> {
                 b'^'
                 | b'\r'
                 | b'\n'
-                | b'0'..=b'7'
+                | b'0'..=b'9'
+                | b'a'..=b'f'
+                | b'A'..=b'F'
                 | b'\\'
-                | b'b'
-                | b'f'
                 | b'n'
                 | b'r'
                 | b't'

crates/biome_css_analyze/tests/specs/suspicious/noUselessEscapeInString/invalid.css

@@ -1,6 +1,8 @@
+/* should generate diagnostics */
+
 .a::after {
-    content: /*before*/ "useless \a" /*after*/
+    content: /*before*/ "useless \z" /*after*/
 }
 .b::after {
     content: "useless \'"
-}
+}

crates/biome_css_analyze/tests/specs/suspicious/noUselessEscapeInString/invalid.css.snap

@@ -4,51 +4,55 @@ expression: invalid.css
 ---
 # Input
 ```css
+/* should generate diagnostics */
+
 .a::after {
-    content: /*before*/ "useless \a" /*after*/
+    content: /*before*/ "useless \z" /*after*/
 }
 .b::after {
     content: "useless \'"
 }
+
 ```
 
 # Diagnostics
 ```
-invalid.css:2:35 lint/suspicious/noUselessEscapeInString  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+invalid.css:4:35 lint/suspicious/noUselessEscapeInString  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 
   ! The character doesn't need to be escaped.
   
-    1 │ .a::after {
-  > 2 │     content: /*before*/ "useless \a" /*after*/
+    3 │ .a::after {
+  > 4 │     content: /*before*/ "useless \z" /*after*/
       │                                   ^
-    3 │ }
-    4 │ .b::after {
+    5 │ }
+    6 │ .b::after {
   
   i Only quotes that enclose the string and special characters need to be escaped.
   
   i Safe fix: Unescape the character.
   
-    2 │ ····content:·/*before*/·"useless·\a"·/*after*/
+    4 │ ····content:·/*before*/·"useless·\z"·/*after*/
       │                                  -            
 
 ```
 
 ```
-invalid.css:5:24 lint/suspicious/noUselessEscapeInString  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+invalid.css:7:24 lint/suspicious/noUselessEscapeInString  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 
   ! The character doesn't need to be escaped.
   
-    3 │ }
-    4 │ .b::after {
-  > 5 │     content: "useless \'"
+    5 │ }
+    6 │ .b::after {
+  > 7 │     content: "useless \'"
       │                        ^
-    6 │ }
+    8 │ }
+    9 │ 
   
   i Only quotes that enclose the string and special characters need to be escaped.
   
   i Safe fix: Unescape the character.
   
-    5 │ ····content:·"useless·\'"
+    7 │ ····content:·"useless·\'"
       │                       -  
 
 ```

crates/biome_css_analyze/tests/specs/suspicious/noUselessEscapeInString/valid.css

@@ -1,7 +1,12 @@
 /* should not generate diagnostics */
+
 .a::after {
     content: "\""
 }
 .b::after {
     content: "\t"
-}
+}
+
+.icon-file:before {
+	content: "\e7bb";
+}

crates/biome_css_analyze/tests/specs/suspicious/noUselessEscapeInString/valid.css.snap

@@ -5,10 +5,16 @@ expression: valid.css
 # Input
 ```css
 /* should not generate diagnostics */
+
 .a::after {
     content: "\""
 }
 .b::after {
     content: "\t"
 }
+
+.icon-file:before {
+	content: "\e7bb";
+}
+
 ```