rustc_errors: use perfect hashing for character replacements

Cargo.lock

@@ -2712,6 +2712,7 @@ version = "0.11.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ade2d8b8f33c7333b51bcf0428d37e217e9f32192ae4772156f65063b8ce03dc"
 dependencies = [
+ "phf_macros",
  "phf_shared 0.11.2",
 ]
 
@@ -2745,6 +2746,19 @@ dependencies = [
  "rand",
 ]
 
+[[package]]
+name = "phf_macros"
+version = "0.11.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3444646e286606587e49f3bcf1679b8cef1dc2c5ecc29ddacaffc305180d464b"
+dependencies = [
+ "phf_generator 0.11.2",
+ "phf_shared 0.11.2",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.67",
+]
+
 [[package]]
 name = "phf_shared"
 version = "0.10.0"
@@ -3653,6 +3667,7 @@ version = "0.0.0"
 dependencies = [
  "annotate-snippets 0.10.2",
  "derive_setters",
+ "phf",
  "rustc_ast",
  "rustc_ast_pretty",
  "rustc_data_structures",

compiler/rustc_errors/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 # tidy-alphabetical-start
 annotate-snippets = "0.10"
 derive_setters = "0.1.6"
+phf = { version = "0.11.2", features = ["macros"] }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_data_structures = { path = "../rustc_data_structures" }

compiler/rustc_errors/src/emitter.rs

@@ -2563,66 +2563,62 @@ fn num_decimal_digits(num: usize) -> usize {
 }
 
 // We replace some characters so the CLI output is always consistent and underlines aligned.
-// Keep the following list in sync with `rustc_span::char_width`.
-// ATTENTION: keep lexicografically sorted so that the binary search will work
-const OUTPUT_REPLACEMENTS: &[(char, &str)] = &[
-    // tidy-alphabetical-start
+const OUTPUT_REPLACEMENTS: phf::Map<char, &'static str> = phf::phf_map![
     // In terminals without Unicode support the following will be garbled, but in *all* terminals
     // the underlying codepoint will be as well. We could gate this replacement behind a "unicode
     // support" gate.
-    ('\0', "␀"),
-    ('\u{0001}', "␁"),
-    ('\u{0002}', "␂"),
-    ('\u{0003}', "␃"),
-    ('\u{0004}', "␄"),
-    ('\u{0005}', "␅"),
-    ('\u{0006}', "␆"),
-    ('\u{0007}', "␇"),
-    ('\u{0008}', "␈"),
-    ('\u{0009}', "    "), // We do our own tab replacement
-    ('\u{000b}', "␋"),
-    ('\u{000c}', "␌"),
-    ('\u{000d}', "␍"),
-    ('\u{000e}', "␎"),
-    ('\u{000f}', "␏"),
-    ('\u{0010}', "␐"),
-    ('\u{0011}', "␑"),
-    ('\u{0012}', "␒"),
-    ('\u{0013}', "␓"),
-    ('\u{0014}', "␔"),
-    ('\u{0015}', "␕"),
-    ('\u{0016}', "␖"),
-    ('\u{0017}', "␗"),
-    ('\u{0018}', "␘"),
-    ('\u{0019}', "␙"),
-    ('\u{001a}', "␚"),
-    ('\u{001b}', "␛"),
-    ('\u{001c}', "␜"),
-    ('\u{001d}', "␝"),
-    ('\u{001e}', "␞"),
-    ('\u{001f}', "␟"),
-    ('\u{007f}', "␡"),
-    ('\u{200d}', ""), // Replace ZWJ for consistent terminal output of grapheme clusters.
-    ('\u{202a}', "�"), // The following unicode text flow control characters are inconsistently
-    ('\u{202b}', "�"), // supported across CLIs and can cause confusion due to the bytes on disk
-    ('\u{202c}', "�"), // not corresponding to the visible source code, so we replace them always.
-    ('\u{202d}', "�"),
-    ('\u{202e}', "�"),
-    ('\u{2066}', "�"),
-    ('\u{2067}', "�"),
-    ('\u{2068}', "�"),
-    ('\u{2069}', "�"),
-    // tidy-alphabetical-end
+    '\0' => "␀",
+    '\t' => "    ", // We do our own tab replacement
+    '\r' => "␍",
+    '\u{0001}' => "␁",
+    '\u{0002}' => "␂",
+    '\u{0003}' => "␃",
+    '\u{0004}' => "␄",
+    '\u{0005}' => "␅",
+    '\u{0006}' => "␆",
+    '\u{0007}' => "␇",
+    '\u{0008}' => "␈",
+    '\u{000b}' => "␋",
+    '\u{000c}' => "␌",
+    '\u{000e}' => "␎",
+    '\u{000f}' => "␏",
+    '\u{0010}' => "␐",
+    '\u{0011}' => "␑",
+    '\u{0012}' => "␒",
+    '\u{0013}' => "␓",
+    '\u{0014}' => "␔",
+    '\u{0015}' => "␕",
+    '\u{0016}' => "␖",
+    '\u{0017}' => "␗",
+    '\u{0018}' => "␘",
+    '\u{0019}' => "␙",
+    '\u{001a}' => "␚",
+    '\u{001b}' => "␛",
+    '\u{001c}' => "␜",
+    '\u{001d}' => "␝",
+    '\u{001e}' => "␞",
+    '\u{001f}' => "␟",
+    '\u{007f}' => "␡",
+    '\u{200d}' => "", // Replace ZWJ for consistent terminal output of grapheme clusters.
+    '\u{202a}' => "�", // The following unicode text flow control characters are inconsistently
+    '\u{202b}' => "�", // supported across CLIs and can cause confusion due to the bytes on disk
+    '\u{202c}' => "�", // not corresponding to the visible source code, so we replace them always.
+    '\u{202d}' => "�",
+    '\u{202e}' => "�",
+    '\u{2066}' => "�",
+    '\u{2067}' => "�",
+    '\u{2068}' => "�",
+    '\u{2069}' => "�",
 ];
 
 fn normalize_whitespace(s: &str) -> String {
-    // Scan the input string for a character in the ordered table above. If it's present, replace
-    // it with it's alternative string (it can be more than 1 char!). Otherwise, retain the input
-    // char. At the end, allocate all chars into a string in one operation.
+    // Scan the input string for a character in the replacement table above.
+    // If it's present, replace it with its alternative string (it can be more than 1 char!).
+    // Otherwise, retain the input char.
     s.chars().fold(String::with_capacity(s.len()), |mut s, c| {
-        match OUTPUT_REPLACEMENTS.binary_search_by_key(&c, |(k, _)| *k) {
-            Ok(i) => s.push_str(OUTPUT_REPLACEMENTS[i].1),
-            _ => s.push(c),
+        match OUTPUT_REPLACEMENTS.get(&c) {
+            Some(r) => s.push_str(r),
+            None => s.push(c),
         }
         s
     })

src/tools/tidy/src/deps.rs

@@ -345,6 +345,10 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "parking_lot_core",
     "pathdiff",
     "perf-event-open-sys",
+    "phf",
+    "phf_generator",
+    "phf_macros",
+    "phf_shared",
     "pin-project-lite",
     "polonius-engine",
     "portable-atomic", // dependency for platforms doesn't support `AtomicU64` in std
@@ -386,6 +390,7 @@ const PERMITTED_RUSTC_DEPENDENCIES: &[&str] = &[
     "sha2",
     "sharded-slab",
     "shlex",
+    "siphasher",
     "smallvec",
     "snap",
     "stable_deref_trait",