Do not provide suggestions for non standard characters

compiler/rustc_lint/src/nonstandard_style.rs

@@ -127,14 +127,20 @@ impl NonCamelCaseTypes {
         if !is_camel_case(name) {
             cx.struct_span_lint(NON_CAMEL_CASE_TYPES, ident.span, |lint| {
                 let msg = format!("{} `{}` should have an upper camel case name", sort, name);
-                lint.build(&msg)
-                    .span_suggestion(
+                let mut err = lint.build(&msg);
+                let cc = to_camel_case(name);
+                // We cannot provide meaningful suggestions
+                // if the characters are in the category of "Lowercase Letter".
+                if name.to_string() != cc {
+                    err.span_suggestion(
                         ident.span,
                         "convert the identifier to upper camel case",
                         to_camel_case(name),
                         Applicability::MaybeIncorrect,
-                    )
-                    .emit()
+                    );
+                }
+
+                err.emit();
             })
         }
     }
@@ -263,17 +269,21 @@ impl NonSnakeCase {
                 let sc = NonSnakeCase::to_snake_case(name);
                 let msg = format!("{} `{}` should have a snake case name", sort, name);
                 let mut err = lint.build(&msg);
-                // We have a valid span in almost all cases, but we don't have one when linting a crate
-                // name provided via the command line.
-                if !ident.span.is_dummy() {
-                    err.span_suggestion(
-                        ident.span,
-                        "convert the identifier to snake case",
-                        sc,
-                        Applicability::MaybeIncorrect,
-                    );
-                } else {
-                    err.help(&format!("convert the identifier to snake case: `{}`", sc));
+                // We cannot provide meaningful suggestions
+                // if the characters are in the category of "Uppercase Letter".
+                if name.to_string() != sc {
+                    // We have a valid span in almost all cases, but we don't have one when linting a crate
+                    // name provided via the command line.
+                    if !ident.span.is_dummy() {
+                        err.span_suggestion(
+                            ident.span,
+                            "convert the identifier to snake case",
+                            sc,
+                            Applicability::MaybeIncorrect,
+                        );
+                    } else {
+                        err.help(&format!("convert the identifier to snake case: `{}`", sc));
+                    }
                 }
 
                 err.emit();
@@ -441,14 +451,20 @@ impl NonUpperCaseGlobals {
         if name.chars().any(|c| c.is_lowercase()) {
             cx.struct_span_lint(NON_UPPER_CASE_GLOBALS, ident.span, |lint| {
                 let uc = NonSnakeCase::to_snake_case(&name).to_uppercase();
-                lint.build(&format!("{} `{}` should have an upper case name", sort, name))
-                    .span_suggestion(
+                let mut err =
+                    lint.build(&format!("{} `{}` should have an upper case name", sort, name));
+                // We cannot provide meaningful suggestions
+                // if the characters are in the category of "Lowercase Letter".
+                if name.to_string() != uc {
+                    err.span_suggestion(
                         ident.span,
                         "convert the identifier to upper case",
                         uc,
                         Applicability::MaybeIncorrect,
-                    )
-                    .emit();
+                    );
+                }
+
+                err.emit();
             })
         }
     }

src/test/ui/lint/special-upper-lower-cases.rs

@@ -0,0 +1,24 @@
+// (#77273) These characters are in the general categories of
+// "Uppercase/Lowercase Letter".
+// The diagnostics don't provide meaningful suggestions for them
+// as we cannot convert them properly.
+
+// check-pass
+
+#![feature(non_ascii_idents)]
+#![allow(uncommon_codepoints, unused)]
+
+struct 𝕟𝕠𝕥𝕒𝕔𝕒𝕞𝕖𝕝;
+//~^ WARN: type `𝕟𝕠𝕥𝕒𝕔𝕒𝕞𝕖𝕝` should have an upper camel case name
+
+// FIXME: How we should handle this?
+struct 𝕟𝕠𝕥_𝕒_𝕔𝕒𝕞𝕖𝕝;
+//~^ WARN: type `𝕟𝕠𝕥_𝕒_𝕔𝕒𝕞𝕖𝕝` should have an upper camel case name
+
+static 𝗻𝗼𝗻𝘂𝗽𝗽𝗲𝗿𝗰𝗮𝘀𝗲: i32 = 1;
+//~^ WARN: static variable `𝗻𝗼𝗻𝘂𝗽𝗽𝗲𝗿𝗰𝗮𝘀𝗲` should have an upper case name
+
+fn main() {
+    let 𝓢𝓝𝓐𝓐𝓐𝓐𝓚𝓔𝓢 = 1;
+    //~^ WARN: variable `𝓢𝓝𝓐𝓐𝓐𝓐𝓚𝓔𝓢` should have a snake case name
+}

src/test/ui/lint/special-upper-lower-cases.stderr

@@ -0,0 +1,32 @@
+warning: type `𝕟𝕠𝕥𝕒𝕔𝕒𝕞𝕖𝕝` should have an upper camel case name
+  --> $DIR/special-upper-lower-cases.rs:11:8
+   |
+LL | struct 𝕟𝕠𝕥𝕒𝕔𝕒𝕞𝕖𝕝;
+   |        ^^^^^^^^^
+   |
+   = note: `#[warn(non_camel_case_types)]` on by default
+
+warning: type `𝕟𝕠𝕥_𝕒_𝕔𝕒𝕞𝕖𝕝` should have an upper camel case name
+  --> $DIR/special-upper-lower-cases.rs:15:8
+   |
+LL | struct 𝕟𝕠𝕥_𝕒_𝕔𝕒𝕞𝕖𝕝;
+   |        ^^^^^^^^^^^ help: convert the identifier to upper camel case: `𝕟𝕠𝕥𝕒𝕔𝕒𝕞𝕖𝕝`
+
+warning: static variable `𝗻𝗼𝗻𝘂𝗽𝗽𝗲𝗿𝗰𝗮𝘀𝗲` should have an upper case name
+  --> $DIR/special-upper-lower-cases.rs:18:8
+   |
+LL | static 𝗻𝗼𝗻𝘂𝗽𝗽𝗲𝗿𝗰𝗮𝘀𝗲: i32 = 1;
+   |        ^^^^^^^^^^^^
+   |
+   = note: `#[warn(non_upper_case_globals)]` on by default
+
+warning: variable `𝓢𝓝𝓐𝓐𝓐𝓐𝓚𝓔𝓢` should have a snake case name
+  --> $DIR/special-upper-lower-cases.rs:22:9
+   |
+LL |     let 𝓢𝓝𝓐𝓐𝓐𝓐𝓚𝓔𝓢 = 1;
+   |         ^^^^^^^^^
+   |
+   = note: `#[warn(non_snake_case)]` on by default
+
+warning: 4 warnings emitted
+