Limit the number of names and values in check-cfg diagnostics

compiler/rustc_lint/src/context/diagnostics.rs

@@ -9,6 +9,47 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::BytePos;
 
+const MAX_CHECK_CFG_NAMES_OR_VALUES: usize = 35;
+
+fn check_cfg_expected_note(
+    possibilities: &[Symbol],
+    type_: &str,
+    name: Option<Symbol>,
+    suffix: &str,
+) -> String {
+    use std::fmt::Write;
+
+    // as an anti-regression test `tests/ui/check-cfg/well-known-values.rs`
+    // needs to have the full list of expected values, so we use this dummy env
+    let n_possibilities = std::cmp::min(
+        possibilities.len(),
+        if std::env::var("RUSTC_PRINT_FULL_CHECK_CFG").is_ok() {
+            possibilities.len()
+        } else {
+            MAX_CHECK_CFG_NAMES_OR_VALUES
+        },
+    );
+
+    let mut possibilities = possibilities.iter().map(Symbol::as_str).collect::<Vec<_>>();
+    possibilities.sort();
+
+    let and_more = possibilities.len().saturating_sub(n_possibilities);
+    let possibilities = possibilities[..n_possibilities].join("`, `");
+
+    let mut note = String::with_capacity(50 + possibilities.len());
+
+    write!(&mut note, "expected {type_}").unwrap();
+    if let Some(name) = name {
+        write!(&mut note, " for `{name}`").unwrap();
+    }
+    write!(&mut note, " are: {suffix}`{possibilities}`").unwrap();
+    if and_more > 0 {
+        write!(&mut note, " and {and_more} more").unwrap();
+    }
+
+    note
+}
+
 pub(super) fn builtin(
     sess: &Session,
     diagnostic: BuiltinLintDiagnostics,
@@ -292,16 +333,7 @@ pub(super) fn builtin(
                     }
                 }
                 if !possibilities.is_empty() {
-                    let mut possibilities =
-                        possibilities.iter().map(Symbol::as_str).collect::<Vec<_>>();
-                    possibilities.sort();
-                    let possibilities = possibilities.join("`, `");
-
-                    // The list of expected names can be long (even by default) and
-                    // so the diagnostic produced can take a lot of space. To avoid
-                    // cloging the user output we only want to print that diagnostic
-                    // once.
-                    db.help_once(format!("expected names are: `{possibilities}`"));
+                    db.help_once(check_cfg_expected_note(&possibilities, "names", None, ""));
                 }
             }
 
@@ -345,16 +377,12 @@ pub(super) fn builtin(
             // Show the full list if all possible values for a given name, but don't do it
             // for names as the possibilities could be very long
             if !possibilities.is_empty() {
-                {
-                    let mut possibilities =
-                        possibilities.iter().map(Symbol::as_str).collect::<Vec<_>>();
-                    possibilities.sort();
-
-                    let possibilities = possibilities.join("`, `");
-                    let none = if have_none_possibility { "(none), " } else { "" };
-
-                    db.note(format!("expected values for `{name}` are: {none}`{possibilities}`"));
-                }
+                db.note(check_cfg_expected_note(
+                    &possibilities,
+                    "values",
+                    Some(name),
+                    if have_none_possibility { "(none), " } else { "" },
+                ));
 
                 if let Some((value, value_span)) = value {
                     // Suggest the most probable if we found one

tests/ui/check-cfg/mix.rs

@@ -74,6 +74,8 @@ fn test_cfg_macro() {
     //~^ WARNING unexpected `cfg` condition value
     //~| WARNING unexpected `cfg` condition value
     //~| WARNING unexpected `cfg` condition value
+    cfg!(target_feature = "zebra");
+    //~^ WARNING unexpected `cfg` condition value
 }
 
 fn main() {}

tests/ui/check-cfg/mix.stderr

@@ -245,5 +245,14 @@ LL |     cfg!(all(feature = "zebra", feature = "zebra", feature = "zebra"));
    = help: to expect this configuration use `--check-cfg=cfg(feature, values("zebra"))`
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
-warning: 26 warnings emitted
+warning: unexpected `cfg` condition value: `zebra`
+  --> $DIR/mix.rs:77:10
+   |
+LL |     cfg!(target_feature = "zebra");
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: expected values for `target_feature` are: `10e60`, `2e3`, `3e3r1`, `3e3r2`, `3e3r3`, `3e7`, `7e10`, `a`, `aclass`, `adx`, `aes`, `altivec`, `alu32`, `atomics`, `avx`, `avx2`, `avx512bf16`, `avx512bitalg`, `avx512bw`, `avx512cd`, `avx512dq`, `avx512er`, `avx512f`, `avx512fp16`, `avx512ifma`, `avx512pf`, `avx512vbmi`, `avx512vbmi2`, `avx512vl`, `avx512vnni`, `avx512vp2intersect`, `avx512vpopcntdq`, `bf16`, `bmi1`, `bmi2` and 186 more
+   = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
+
+warning: 27 warnings emitted
 

tests/ui/check-cfg/well-known-values.rs

@@ -6,6 +6,7 @@
 //
 //@ check-pass
 //@ compile-flags: --check-cfg=cfg() -Z unstable-options
+//@ rustc-env:RUSTC_PRINT_FULL_CHECK_CFG=1
 
 #![feature(cfg_overflow_checks)]
 #![feature(cfg_relocation_model)]

tests/ui/check-cfg/well-known-values.stderr

@@ -1,5 +1,5 @@
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:26:5
+  --> $DIR/well-known-values.rs:27:5
    |
 LL |     clippy = "_UNEXPECTED_VALUE",
    |     ^^^^^^----------------------
@@ -11,7 +11,7 @@ LL |     clippy = "_UNEXPECTED_VALUE",
    = note: `#[warn(unexpected_cfgs)]` on by default
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:28:5
+  --> $DIR/well-known-values.rs:29:5
    |
 LL |     debug_assertions = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^----------------------
@@ -22,7 +22,7 @@ LL |     debug_assertions = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:30:5
+  --> $DIR/well-known-values.rs:31:5
    |
 LL |     doc = "_UNEXPECTED_VALUE",
    |     ^^^----------------------
@@ -33,7 +33,7 @@ LL |     doc = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:32:5
+  --> $DIR/well-known-values.rs:33:5
    |
 LL |     doctest = "_UNEXPECTED_VALUE",
    |     ^^^^^^^----------------------
@@ -44,7 +44,7 @@ LL |     doctest = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:34:5
+  --> $DIR/well-known-values.rs:35:5
    |
 LL |     miri = "_UNEXPECTED_VALUE",
    |     ^^^^----------------------
@@ -55,7 +55,7 @@ LL |     miri = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:36:5
+  --> $DIR/well-known-values.rs:37:5
    |
 LL |     overflow_checks = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^----------------------
@@ -66,7 +66,7 @@ LL |     overflow_checks = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:38:5
+  --> $DIR/well-known-values.rs:39:5
    |
 LL |     panic = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -75,7 +75,7 @@ LL |     panic = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:40:5
+  --> $DIR/well-known-values.rs:41:5
    |
 LL |     proc_macro = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^----------------------
@@ -86,7 +86,7 @@ LL |     proc_macro = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:42:5
+  --> $DIR/well-known-values.rs:43:5
    |
 LL |     relocation_model = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -95,7 +95,7 @@ LL |     relocation_model = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:44:5
+  --> $DIR/well-known-values.rs:45:5
    |
 LL |     sanitize = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -104,7 +104,7 @@ LL |     sanitize = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:46:5
+  --> $DIR/well-known-values.rs:47:5
    |
 LL |     target_abi = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -113,7 +113,7 @@ LL |     target_abi = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:48:5
+  --> $DIR/well-known-values.rs:49:5
    |
 LL |     target_arch = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -122,7 +122,7 @@ LL |     target_arch = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:50:5
+  --> $DIR/well-known-values.rs:51:5
    |
 LL |     target_endian = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -131,7 +131,7 @@ LL |     target_endian = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:52:5
+  --> $DIR/well-known-values.rs:53:5
    |
 LL |     target_env = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -140,7 +140,7 @@ LL |     target_env = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:54:5
+  --> $DIR/well-known-values.rs:55:5
    |
 LL |     target_family = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -149,7 +149,7 @@ LL |     target_family = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:56:5
+  --> $DIR/well-known-values.rs:57:5
    |
 LL |     target_feature = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -158,7 +158,7 @@ LL |     target_feature = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:58:5
+  --> $DIR/well-known-values.rs:59:5
    |
 LL |     target_has_atomic = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -167,7 +167,7 @@ LL |     target_has_atomic = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:60:5
+  --> $DIR/well-known-values.rs:61:5
    |
 LL |     target_has_atomic_equal_alignment = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -176,7 +176,7 @@ LL |     target_has_atomic_equal_alignment = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:62:5
+  --> $DIR/well-known-values.rs:63:5
    |
 LL |     target_has_atomic_load_store = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -185,7 +185,7 @@ LL |     target_has_atomic_load_store = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:64:5
+  --> $DIR/well-known-values.rs:65:5
    |
 LL |     target_os = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -194,7 +194,7 @@ LL |     target_os = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:66:5
+  --> $DIR/well-known-values.rs:67:5
    |
 LL |     target_pointer_width = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -203,7 +203,7 @@ LL |     target_pointer_width = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:68:5
+  --> $DIR/well-known-values.rs:69:5
    |
 LL |     target_thread_local = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^----------------------
@@ -214,7 +214,7 @@ LL |     target_thread_local = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:70:5
+  --> $DIR/well-known-values.rs:71:5
    |
 LL |     target_vendor = "_UNEXPECTED_VALUE",
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -223,7 +223,7 @@ LL |     target_vendor = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:72:5
+  --> $DIR/well-known-values.rs:73:5
    |
 LL |     test = "_UNEXPECTED_VALUE",
    |     ^^^^----------------------
@@ -234,7 +234,7 @@ LL |     test = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:74:5
+  --> $DIR/well-known-values.rs:75:5
    |
 LL |     unix = "_UNEXPECTED_VALUE",
    |     ^^^^----------------------
@@ -245,7 +245,7 @@ LL |     unix = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `_UNEXPECTED_VALUE`
-  --> $DIR/well-known-values.rs:76:5
+  --> $DIR/well-known-values.rs:77:5
    |
 LL |     windows = "_UNEXPECTED_VALUE",
    |     ^^^^^^^----------------------
@@ -256,7 +256,7 @@ LL |     windows = "_UNEXPECTED_VALUE",
    = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `linuz`
-  --> $DIR/well-known-values.rs:82:7
+  --> $DIR/well-known-values.rs:83:7
    |
 LL | #[cfg(target_os = "linuz")] // testing that we suggest `linux`
    |       ^^^^^^^^^^^^-------