Introduce `-Zmacro-stats`.

It collects data about macro expansions and prints them in a table after
expansion finishes. It's very useful for detecting macro bloat,
especially for proc macros.

Details:
- It measures code snippets by pretty-printing them and then measuring
  lines and bytes. This required a bunch of additional pretty-printing
  plumbing, in `rustc_ast_pretty` and `rustc_expand`.
- The measurement is done in `MacroExpander::expand_invoc`.
- The measurements are stored in `ExtCtxt::macro_stats`.

3 files changed, 159 insertions, 0 deletions

diff --git a/tests/ui/stats/auxiliary/include.rs b/tests/ui/stats/auxiliary/include.rs
new file mode 100644
index 00000000000..7fb7c781137
--- /dev/null
+++ b/tests/ui/stats/auxiliary/include.rs
@@ -0,0 +1,3 @@
+fn zzz(x: u32) -> u32 {
+    x
+}
diff --git a/tests/ui/stats/macro-stats.rs b/tests/ui/stats/macro-stats.rs
new file mode 100644
index 00000000000..ee265d682fd
--- /dev/null
+++ b/tests/ui/stats/macro-stats.rs
@@ -0,0 +1,130 @@
+//@ check-pass
+//@ compile-flags: -Zmacro-stats
+
+#[test]
+fn test_foo() {
+    let what = "this";
+    let how = "completely";
+    let when = "immediately";
+    println!("{what} disappears {how} and {when}");
+}
+
+#[rustfmt::skip] // non-macro attr, ignored by `-Zmacro-stats`
+fn rustfmt_skip() {
+    // Nothing to see here.
+}
+
+#[derive(Default, Clone, Copy, Hash)]
+enum E1 {
+    #[default] // non-macro attr, ignored by `-Zmacro-stats`
+    A,
+    B,
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct E2 {
+    a: u32,
+    b: String,
+    c: Vec<bool>,
+}
+
+#[derive(Clone)] struct S0;
+#[derive(Clone)] struct S1(u32);
+#[derive(Clone)] struct S2(u32, u32);
+#[derive(Clone)] struct S3(u32, u32, u32);
+#[derive(Clone)] struct S4(u32, u32, u32, u32);
+#[derive(Clone)] struct S5(u32, u32, u32, u32, u32);
+
+macro_rules! u32 {
+    () => { u32 }
+}
+
+macro_rules! none {
+    () => { None }
+}
+fn opt(x: Option<u32>) {
+    match x {
+        Some(_) => {}
+        none!() => {}           // AstFragmentKind::Pat
+    }
+}
+
+macro_rules! this_is_a_really_really_long_macro_name {
+    ($t:ty) => {
+        fn f(_: $t) {}
+    }
+}
+this_is_a_really_really_long_macro_name!(u32!()); // AstFragmentKind::{Items,Ty}
+
+macro_rules! trait_tys {
+    () => {
+        type A;
+        type B;
+    }
+}
+trait Tr {
+    trait_tys!();               // AstFragmentKind::TraitItems
+}
+
+macro_rules! impl_const { () => { const X: u32 = 0; } }
+struct U;
+impl U {
+    impl_const!();              // AstFragmentKind::ImplItems
+}
+
+macro_rules! trait_impl_tys {
+    () => {
+        type A = u32;
+        type B = bool;
+    }
+}
+struct Tr1;
+impl Tr for Tr1 {
+    trait_impl_tys!();          // AstFragment::TraitImplItems
+}
+
+macro_rules! foreign_item {
+    () => { fn fc(a: u32) -> u32; }
+}
+extern "C" {
+    foreign_item!();            // AstFragment::ForeignItems
+}
+
+// Include macros are ignored by `-Zmacro-stats`.
+mod includes {
+    mod z1 {
+        include!("auxiliary/include.rs");
+    }
+    mod z2 {
+        std::include!("auxiliary/include.rs");
+    }
+
+    const B1: &[u8] = include_bytes!("auxiliary/include.rs");
+    const B2: &[u8] = std::include_bytes!("auxiliary/include.rs");
+
+    const S1: &str = include_str!("auxiliary/include.rs");
+    const S2: &str = std::include_str!("auxiliary/include.rs");
+}
+
+fn main() {
+    macro_rules! n99 {
+        () => { 99 }
+    }
+    let x = n99!() + n99!();    // AstFragmentKind::Expr
+
+    macro_rules! p {
+        () => {
+            // blah
+            let x = 1;
+            let y = x;
+            let _ = y;
+        }
+    }
+    p!();                       // AstFragmentKind::Stmts
+
+    macro_rules! q {
+        () => {};
+        ($($x:ident),*) => { $( let $x: u32 = 12345; )* };
+    }
+    q!(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z);
+}
diff --git a/tests/ui/stats/macro-stats.stderr b/tests/ui/stats/macro-stats.stderr
new file mode 100644
index 00000000000..f87e34622b9
--- /dev/null
+++ b/tests/ui/stats/macro-stats.stderr
@@ -0,0 +1,26 @@
+macro-stats ===================================================================================
+macro-stats MACRO EXPANSION STATS: macro_stats
+macro-stats Macro Name                         Uses      Lines  Avg Lines      Bytes  Avg Bytes
+macro-stats -----------------------------------------------------------------------------------
+macro-stats #[derive(Clone)]                      8         56        7.0      1_660      207.5
+macro-stats #[derive(PartialOrd)]                 1         16       16.0        654      654.0
+macro-stats #[derive(Hash)]                       2         15        7.5        547      273.5
+macro-stats #[derive(Ord)]                        1         14       14.0        489      489.0
+macro-stats q!                                    1         24       24.0        435      435.0
+macro-stats #[derive(Default)]                    2         14        7.0        367      183.5
+macro-stats #[derive(Eq)]                         1         10       10.0        312      312.0
+macro-stats #[derive(Debug)]                      1          7        7.0        261      261.0
+macro-stats #[derive(PartialEq)]                  1          8        8.0        247      247.0
+macro-stats #[derive(Copy)]                       1          1        1.0         46       46.0
+macro-stats p!                                    1          2        2.0         28       28.0
+macro-stats trait_impl_tys!                       1          1        1.0         11       11.0
+macro-stats foreign_item!                         1          0        0.0          6        6.0
+macro-stats impl_const!                           1          0        0.0          4        4.0
+macro-stats trait_tys!                            1          1        1.0          3        3.0
+macro-stats u32!                                  1          0        0.0         -3       -3.0
+macro-stats none!                                 1          0        0.0         -3       -3.0
+macro-stats n99!                                  2          0        0.0         -8       -4.0
+macro-stats this_is_a_really_really_long_macro_name!
+macro-stats                                       1          0        0.0        -30      -30.0
+macro-stats #[test]                               1         -6       -6.0       -158     -158.0
+macro-stats ===================================================================================