HeaderValue::from_static can be const

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
           - stable
           - beta
           - nightly
-          - 1.39.0
+          - 1.46.0
 
         include:
           - rust: nightly

src/header/value.rs

@@ -57,12 +57,16 @@ impl HeaderValue {
     /// assert_eq!(val, "hello");
     /// ```
     #[inline]
-    pub fn from_static(src: &'static str) -> HeaderValue {
+    #[allow(unconditional_panic)] // required for the panic circumventon
+    #[track_caller]
+    pub const fn from_static(src: &'static str) -> HeaderValue {
         let bytes = src.as_bytes();
-        for &b in bytes {
-            if !is_visible_ascii(b) {
-                panic!("invalid header value");
+        let mut i = 0;
+        while i < bytes.len() {
+            if !is_visible_ascii(bytes[i]) {
+                ([] as [u8; 0])[0]; // Invalid header value
             }
+            i += 1;
         }
 
         HeaderValue {
@@ -555,7 +559,7 @@ mod try_from_header_name_tests {
     }
 }
 
-fn is_visible_ascii(b: u8) -> bool {
+const fn is_visible_ascii(b: u8) -> bool {
     b >= 32 && b < 127 || b == b'\t'
 }