Multiline string attr display

[GuillaumeGomez]

Fixes #81482.

As you see here (or on the screenshot below):

The backslash is kept in the string literal in the end. This fix removes it, however I wonder if there isn't a function to do that already in the compiler (couldn't find anything so...). Maybe you might have some information about it @oli-obk ?

cc @CraftSpider
r? @camelid

[oli-obk]

We definitely have code for this somewhere already. I would actually have expected the parser to handle this for us so we don't ever see this.

[camelid]

I think the issue is that we get the attributes using:

        .filter_map(|attr| {
            if ALLOWED_ATTRIBUTES.contains(&attr.name_or_empty()) {
                Some(pprust::attribute_to_string(&attr))
            } else {
                None
            }
        })

which seems very hacky.

[camelid]

I think we want to use something like Attribute::value_str instead of the pretty-printer. Can you try that?

@rustbot label: -S-waiting-on-review +S-waiting-on-author

[GuillaumeGomez]

The problem here is that we print not only the value but the whole attr. So here, we print #[must_use = "blablabla"], no just "blablabla".

[oli-obk]

maybe we can fix the pretty printer to use value_str?

[GuillaumeGomez]

Sounds like a good idea! I'll go with this then.

[GuillaumeGomez]

It seems that the pretty printer cannot really use value_str as we go through multiple steps and in the end just finish with a ast::Literal. We can still make it remove the backslash though (diff of what I did):

diff --git a/compiler/rustc_ast/src/util/literal.rs b/compiler/rustc_ast/src/util/literal.rs
index 2124f1efb99..cf0f6ef3b2b 100644
--- a/compiler/rustc_ast/src/util/literal.rs
+++ b/compiler/rustc_ast/src/util/literal.rs
@@ -23,7 +23,7 @@ pub enum LitError {
 
 impl LitKind {
     /// Converts literal token into a semantic literal.
-    fn from_lit_token(lit: token::Lit) -> Result<LitKind, LitError> {
+    pub fn from_lit_token(lit: token::Lit) -> Result<LitKind, LitError> {
         let token::Lit { kind, symbol, suffix } = lit;
         if suffix.is_some() && !kind.may_have_suffix() {
             return Err(LitError::InvalidSuffix);
diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index 2c8caf68f00..b79398035c6 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -191,13 +191,49 @@ pub fn literal_to_string(lit: token::Lit) -> String {
     let mut out = match kind {
         token::Byte => format!("b'{}'", symbol),
         token::Char => format!("'{}'", symbol),
-        token::Str => format!("\"{}\"", symbol),
+        token::Str => {
+            if let Ok(ast::LitKind::Str(symbol, _)) = ast::LitKind::from_lit_token(lit) {
+                format!("\"{}\"", symbol)
+            } else {
+                format!("\"{}\"", symbol)
+            }
+        }
         token::StrRaw(n) => {
-            format!("r{delim}\"{string}\"{delim}", delim = "#".repeat(n as usize), string = symbol)
+            if let Ok(ast::LitKind::Str(symbol, _)) = ast::LitKind::from_lit_token(lit) {
+                format!(
+                    "r{delim}\"{string}\"{delim}",
+                    delim = "#".repeat(n as usize),
+                    string = symbol
+                )
+            } else {
+                format!(
+                    "r{delim}\"{string}\"{delim}",
+                    delim = "#".repeat(n as usize),
+                    string = symbol
+                )
+            }
+        }
+        token::ByteStr => {
+            if let Ok(l) = ast::LitKind::from_lit_token(lit) {
+                format!("b\"{}\"", l.to_lit_token().symbol)
+            } else {
+                format!("b\"{}\"", symbol)
+            }
         }
-        token::ByteStr => format!("b\"{}\"", symbol),
         token::ByteStrRaw(n) => {
-            format!("br{delim}\"{string}\"{delim}", delim = "#".repeat(n as usize), string = symbol)
+            if let Ok(l) = ast::LitKind::from_lit_token(lit) {
+                format!(
+                    "br{delim}\"{string}\"{delim}",
+                    delim = "#".repeat(n as usize),
+                    string = l.to_lit_token().symbol
+                )
+            } else {
+                format!(
+                    "br{delim}\"{string}\"{delim}",
+                    delim = "#".repeat(n as usize),
+                    string = symbol
+                )
+            }
         }
         token::Integer | token::Float | token::Bool | token::Err => symbol.to_string(),
     };

So in the meantime, I opened a discussion about it in zulip here.

One extra thing to be added here would be a test to ensure that the sources display still has the original content too.

[bors]

☔ The latest upstream changes (presumably #83880) made this pull request unmergeable. Please resolve the merge conflicts.

[jsha]

This is not needed so badly anymore since we removed must_use from ALLOWED_ATTRIBUTES. Do you still want to get this done?

[camelid]

I'm going to close this for now since this PR isn't actionable.