From 86f2d424c8cda473aa1bf91365f499cfe520c54a Mon Sep 17 00:00:00 2001 From: Marijn Schouten Date: Mon, 15 Sep 2025 11:35:08 +0000 Subject: [PATCH] indexing: reword help Co-authored-by: beef --- .../src/error_codes/E0608.md | 15 ++++++++--- compiler/rustc_hir_typeck/src/expr.rs | 27 +++++-------------- tests/ui/indexing/index_message.stderr | 4 ++- tests/ui/issues/issue-27842.stderr | 12 ++++----- tests/ui/span/suggestion-non-ascii.stderr | 4 ++- ...for-indexing-expression-issue-40861.stderr | 2 +- 6 files changed, 30 insertions(+), 34 deletions(-) diff --git a/compiler/rustc_error_codes/src/error_codes/E0608.md b/compiler/rustc_error_codes/src/error_codes/E0608.md index d0ebc3a26f082..3c29484f575ce 100644 --- a/compiler/rustc_error_codes/src/error_codes/E0608.md +++ b/compiler/rustc_error_codes/src/error_codes/E0608.md @@ -1,5 +1,5 @@ -An attempt to use index on a type which doesn't implement the `std::ops::Index` -trait was performed. +Attempted to index a value whose type doesn't implement the +`std::ops::Index` trait. Erroneous code example: @@ -7,8 +7,8 @@ Erroneous code example: 0u8[2]; // error: cannot index into a value of type `u8` ``` -To be able to index into a type it needs to implement the `std::ops::Index` -trait. Example: +Only values with types that implement the `std::ops::Index` trait +can be indexed with square brackets. Example: ``` let v: Vec = vec![0, 1, 2, 3]; @@ -16,3 +16,10 @@ let v: Vec = vec![0, 1, 2, 3]; // The `Vec` type implements the `Index` trait so you can do: println!("{}", v[2]); ``` + +Tuples and structs are indexed with dot (`.`), not with brackets (`[]`), +and tuple element names are their positions: +```ignore(pseudo code) +// this (pseudo code) expression is true for any tuple: +tuple == (tuple.0, tuple.1, ...) +``` diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs index d1ce0afddf91c..f9cdc923670f0 100644 --- a/compiler/rustc_hir_typeck/src/expr.rs +++ b/compiler/rustc_hir_typeck/src/expr.rs @@ -3551,35 +3551,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { ); // Try to give some advice about indexing tuples. if let ty::Tuple(types) = base_t.kind() { - let mut needs_note = true; - // If the index is an integer, we can show the actual - // fixed expression: + err.help( + "tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc.", + ); + // If index is an unsuffixed integer, show the fixed expression: if let ExprKind::Lit(lit) = idx.kind && let ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) = lit.node - && i.get() - < types - .len() - .try_into() - .expect("expected tuple index to be < usize length") + && i.get() < types.len().try_into().expect("tuple length fits in u128") { err.span_suggestion( brackets_span, - "to access tuple elements, use", + format!("to access tuple element `{i}`, use"), format!(".{i}"), Applicability::MachineApplicable, ); - needs_note = false; - } else if let ExprKind::Path(..) = idx.peel_borrows().kind { - err.span_label( - idx.span, - "cannot access tuple elements at a variable index", - ); - } - if needs_note { - err.help( - "to access tuple elements, use tuple indexing \ - syntax (e.g., `tuple.0`)", - ); } } diff --git a/tests/ui/indexing/index_message.stderr b/tests/ui/indexing/index_message.stderr index 6affb1ed96252..b6f61379f2af5 100644 --- a/tests/ui/indexing/index_message.stderr +++ b/tests/ui/indexing/index_message.stderr @@ -2,7 +2,9 @@ error[E0608]: cannot index into a value of type `({integer},)` --> $DIR/index_message.rs:3:14 | LL | let _ = z[0]; - | ^^^ help: to access tuple elements, use: `.0` + | ^^^ help: to access tuple element `0`, use: `.0` + | + = help: tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc. error: aborting due to 1 previous error diff --git a/tests/ui/issues/issue-27842.stderr b/tests/ui/issues/issue-27842.stderr index b18fe1512b50b..f388fdf85cde5 100644 --- a/tests/ui/issues/issue-27842.stderr +++ b/tests/ui/issues/issue-27842.stderr @@ -2,17 +2,17 @@ error[E0608]: cannot index into a value of type `({integer}, {integer}, {integer --> $DIR/issue-27842.rs:4:16 | LL | let _ = tup[0]; - | ^^^ help: to access tuple elements, use: `.0` + | ^^^ help: to access tuple element `0`, use: `.0` + | + = help: tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc. error[E0608]: cannot index into a value of type `({integer}, {integer}, {integer})` --> $DIR/issue-27842.rs:9:16 | LL | let _ = tup[i]; - | ^-^ - | | - | cannot access tuple elements at a variable index + | ^^^ | - = help: to access tuple elements, use tuple indexing syntax (e.g., `tuple.0`) + = help: tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc. error[E0608]: cannot index into a value of type `({integer},)` --> $DIR/issue-27842.rs:14:16 @@ -20,7 +20,7 @@ error[E0608]: cannot index into a value of type `({integer},)` LL | let _ = tup[3]; | ^^^ | - = help: to access tuple elements, use tuple indexing syntax (e.g., `tuple.0`) + = help: tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc. error: aborting due to 3 previous errors diff --git a/tests/ui/span/suggestion-non-ascii.stderr b/tests/ui/span/suggestion-non-ascii.stderr index 6e6e31a5698b8..361f744ee8eb6 100644 --- a/tests/ui/span/suggestion-non-ascii.stderr +++ b/tests/ui/span/suggestion-non-ascii.stderr @@ -2,7 +2,9 @@ error[E0608]: cannot index into a value of type `({integer},)` --> $DIR/suggestion-non-ascii.rs:3:24 | LL | println!("☃{}", tup[0]); - | ^^^ help: to access tuple elements, use: `.0` + | ^^^ help: to access tuple element `0`, use: `.0` + | + = help: tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc. error: aborting due to 1 previous error diff --git a/tests/ui/typeck/coercion-check-for-indexing-expression-issue-40861.stderr b/tests/ui/typeck/coercion-check-for-indexing-expression-issue-40861.stderr index 13bc0cd94f37c..ef5f1786801a1 100644 --- a/tests/ui/typeck/coercion-check-for-indexing-expression-issue-40861.stderr +++ b/tests/ui/typeck/coercion-check-for-indexing-expression-issue-40861.stderr @@ -4,7 +4,7 @@ error[E0608]: cannot index into a value of type `()` LL | ()[f(&[1.0])]; | ^^^^^^^^^^^ | - = help: to access tuple elements, use tuple indexing syntax (e.g., `tuple.0`) + = help: tuples are indexed with a dot and a literal index: `tuple.0`, `tuple.1`, etc. error: aborting due to 1 previous error