Rollup merge of #91607 - FabianWolff:issue-91560-const-span, r=jackh726

Make `span_extend_to_prev_str()` more robust

Fixes #91560. The logic in `span_extend_to_prev_str()` is currently quite brittle and fails if there is extra whitespace or something else in between, and it also should return an `Option` but doesn't currently.

Author: matthiaskrgr

compiler/rustc_resolve/src/diagnostics.rs

@@ -453,28 +453,28 @@ impl<'a> Resolver<'a> {
                 // edit:
                 // only do this if the const and usage of the non-constant value are on the same line
                 // the further the two are apart, the higher the chance of the suggestion being wrong
-                // also make sure that the pos for the suggestion is not 0 (ICE #90878)
 
-                let sp =
-                    self.session.source_map().span_extend_to_prev_str(ident.span, current, true);
-
-                let pos_for_suggestion = sp.lo().0.saturating_sub(current.len() as u32);
+                let sp = self
+                    .session
+                    .source_map()
+                    .span_extend_to_prev_str(ident.span, current, true, false);
 
-                if sp.lo().0 == 0
-                    || pos_for_suggestion == 0
-                    || self.session.source_map().is_multiline(sp)
-                {
-                    err.span_label(ident.span, &format!("this would need to be a `{}`", sugg));
-                } else {
-                    let sp = sp.with_lo(BytePos(pos_for_suggestion));
-                    err.span_suggestion(
-                        sp,
-                        &format!("consider using `{}` instead of `{}`", sugg, current),
-                        format!("{} {}", sugg, ident),
-                        Applicability::MaybeIncorrect,
-                    );
-                    err.span_label(span, "non-constant value");
+                match sp {
+                    Some(sp) if !self.session.source_map().is_multiline(sp) => {
+                        let sp = sp.with_lo(BytePos(sp.lo().0 - (current.len() as u32)));
+                        err.span_suggestion(
+                            sp,
+                            &format!("consider using `{}` instead of `{}`", sugg, current),
+                            format!("{} {}", sugg, ident),
+                            Applicability::MaybeIncorrect,
+                        );
+                        err.span_label(span, "non-constant value");
+                    }
+                    _ => {
+                        err.span_label(ident.span, &format!("this would need to be a `{}`", sugg));
+                    }
                 }
+
                 err
             }
             ResolutionError::BindingShadowsSomethingUnacceptable {

compiler/rustc_span/src/source_map.rs

@@ -629,26 +629,41 @@ impl SourceMap {
     }
 
     /// Extends the given `Span` to just after the previous occurrence of `pat` when surrounded by
-    /// whitespace. Returns the same span if no character could be found or if an error occurred
-    /// while retrieving the code snippet.
-    pub fn span_extend_to_prev_str(&self, sp: Span, pat: &str, accept_newlines: bool) -> Span {
+    /// whitespace. Returns None if the pattern could not be found or if an error occurred while
+    /// retrieving the code snippet.
+    pub fn span_extend_to_prev_str(
+        &self,
+        sp: Span,
+        pat: &str,
+        accept_newlines: bool,
+        include_whitespace: bool,
+    ) -> Option<Span> {
         // assure that the pattern is delimited, to avoid the following
         //     fn my_fn()
         //           ^^^^ returned span without the check
         //     ---------- correct span
+        let prev_source = self.span_to_prev_source(sp).ok()?;
         for ws in &[" ", "\t", "\n"] {
             let pat = pat.to_owned() + ws;
-            if let Ok(prev_source) = self.span_to_prev_source(sp) {
-                let prev_source = prev_source.rsplit(&pat).next().unwrap_or("").trim_start();
-                if prev_source.is_empty() && sp.lo().0 != 0 {
-                    return sp.with_lo(BytePos(sp.lo().0 - 1));
-                } else if accept_newlines || !prev_source.contains('\n') {
-                    return sp.with_lo(BytePos(sp.lo().0 - prev_source.len() as u32));
+            if let Some(pat_pos) = prev_source.rfind(&pat) {
+                let just_after_pat_pos = pat_pos + pat.len() - 1;
+                let just_after_pat_plus_ws = if include_whitespace {
+                    just_after_pat_pos
+                        + prev_source[just_after_pat_pos..]
+                            .find(|c: char| !c.is_whitespace())
+                            .unwrap_or(0)
+                } else {
+                    just_after_pat_pos
+                };
+                let len = prev_source.len() - just_after_pat_plus_ws;
+                let prev_source = &prev_source[just_after_pat_plus_ws..];
+                if accept_newlines || !prev_source.trim_start().contains('\n') {
+                    return Some(sp.with_lo(BytePos(sp.lo().0 - len as u32)));
                 }
             }
         }
 
-        sp
+        None
     }
 
     /// Returns the source snippet as `String` after the given `Span`.
@@ -927,7 +942,7 @@ impl SourceMap {
     }
 
     pub fn generate_fn_name_span(&self, span: Span) -> Option<Span> {
-        let prev_span = self.span_extend_to_prev_str(span, "fn", true);
+        let prev_span = self.span_extend_to_prev_str(span, "fn", true, true).unwrap_or(span);
         if let Ok(snippet) = self.span_to_snippet(prev_span) {
             debug!(
                 "generate_fn_name_span: span={:?}, prev_span={:?}, snippet={:?}",
@@ -968,8 +983,7 @@ impl SourceMap {
     pub fn generate_local_type_param_snippet(&self, span: Span) -> Option<(Span, String)> {
         // Try to extend the span to the previous "fn" keyword to retrieve the function
         // signature.
-        let sugg_span = self.span_extend_to_prev_str(span, "fn", false);
-        if sugg_span != span {
+        if let Some(sugg_span) = self.span_extend_to_prev_str(span, "fn", false, true) {
             if let Ok(snippet) = self.span_to_snippet(sugg_span) {
                 // Consume the function name.
                 let mut offset = snippet

src/test/ui/asm/aarch64/parse-error.stderr

@@ -382,7 +382,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:39:37
    |
 LL |     let mut foo = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const foo`
+   |     ----------- help: consider using `const` instead of `let`: `const foo`
 ...
 LL |         asm!("{}", options(), const foo);
    |                                     ^^^ non-constant value
@@ -391,7 +391,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:48:44
    |
 LL |     let mut foo = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const foo`
+   |     ----------- help: consider using `const` instead of `let`: `const foo`
 ...
 LL |         asm!("{}", clobber_abi("C"), const foo);
    |                                            ^^^ non-constant value
@@ -400,7 +400,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:55:31
    |
 LL |     let mut foo = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const foo`
+   |     ----------- help: consider using `const` instead of `let`: `const foo`
 ...
 LL |         asm!("{a}", a = const foo, a = const bar);
    |                               ^^^ non-constant value
@@ -409,7 +409,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:55:46
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{a}", a = const foo, a = const bar);
    |                                              ^^^ non-constant value
@@ -418,7 +418,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:62:45
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{a}", in("x0") foo, a = const bar);
    |                                             ^^^ non-constant value
@@ -427,7 +427,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:65:45
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{a}", in("x0") foo, a = const bar);
    |                                             ^^^ non-constant value
@@ -436,7 +436,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:68:41
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{1}", in("x0") foo, const bar);
    |                                         ^^^ non-constant value

src/test/ui/asm/x86_64/parse-error.stderr

@@ -394,7 +394,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:39:37
    |
 LL |     let mut foo = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const foo`
+   |     ----------- help: consider using `const` instead of `let`: `const foo`
 ...
 LL |         asm!("{}", options(), const foo);
    |                                     ^^^ non-constant value
@@ -403,7 +403,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:50:44
    |
 LL |     let mut foo = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const foo`
+   |     ----------- help: consider using `const` instead of `let`: `const foo`
 ...
 LL |         asm!("{}", clobber_abi("C"), const foo);
    |                                            ^^^ non-constant value
@@ -412,7 +412,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:57:31
    |
 LL |     let mut foo = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const foo`
+   |     ----------- help: consider using `const` instead of `let`: `const foo`
 ...
 LL |         asm!("{a}", a = const foo, a = const bar);
    |                               ^^^ non-constant value
@@ -421,7 +421,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:57:46
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{a}", a = const foo, a = const bar);
    |                                              ^^^ non-constant value
@@ -430,7 +430,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:64:46
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{a}", in("eax") foo, a = const bar);
    |                                              ^^^ non-constant value
@@ -439,7 +439,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:67:46
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{a}", in("eax") foo, a = const bar);
    |                                              ^^^ non-constant value
@@ -448,7 +448,7 @@ error[E0435]: attempt to use a non-constant value in a constant
   --> $DIR/parse-error.rs:70:42
    |
 LL |     let mut bar = 0;
-   |      ---------- help: consider using `const` instead of `let`: `const bar`
+   |     ----------- help: consider using `const` instead of `let`: `const bar`
 ...
 LL |         asm!("{1}", in("eax") foo, const bar);
    |                                          ^^^ non-constant value

src/test/ui/consts/issue-91560.fixed

@@ -0,0 +1,21 @@
+// Regression test for issue #91560.
+
+// run-rustfix
+
+#![allow(unused,non_upper_case_globals)]
+
+fn foo() {
+    const length: usize = 2;
+    //~^ HELP: consider using `const`
+    let arr = [0; length];
+    //~^ ERROR: attempt to use a non-constant value in a constant [E0435]
+}
+
+fn bar() {
+    const length: usize = 2;
+    //~^ HELP: consider using `const`
+    let arr = [0; length];
+    //~^ ERROR: attempt to use a non-constant value in a constant [E0435]
+}
+
+fn main() {}

src/test/ui/consts/issue-91560.rs

@@ -0,0 +1,21 @@
+// Regression test for issue #91560.
+
+// run-rustfix
+
+#![allow(unused,non_upper_case_globals)]
+
+fn foo() {
+    let mut length: usize = 2;
+    //~^ HELP: consider using `const`
+    let arr = [0; length];
+    //~^ ERROR: attempt to use a non-constant value in a constant [E0435]
+}
+
+fn bar() {
+    let   length: usize = 2;
+    //~^ HELP: consider using `const`
+    let arr = [0; length];
+    //~^ ERROR: attempt to use a non-constant value in a constant [E0435]
+}
+
+fn main() {}

src/test/ui/consts/issue-91560.stderr

@@ -0,0 +1,21 @@
+error[E0435]: attempt to use a non-constant value in a constant
+  --> $DIR/issue-91560.rs:10:19
+   |
+LL |     let mut length: usize = 2;
+   |     -------------- help: consider using `const` instead of `let`: `const length`
+LL |
+LL |     let arr = [0; length];
+   |                   ^^^^^^ non-constant value
+
+error[E0435]: attempt to use a non-constant value in a constant
+  --> $DIR/issue-91560.rs:17:19
+   |
+LL |     let   length: usize = 2;
+   |     ------------ help: consider using `const` instead of `let`: `const length`
+LL |
+LL |     let arr = [0; length];
+   |                   ^^^^^^ non-constant value
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0435`.