test: 💍 add ui tests and some docs

Author: richard-uk1

compiler/rustc_lexer/src/lib.rs

@@ -604,6 +604,8 @@ impl Cursor<'_> {
         }
     }
 
+    /// Parses a number and in `.1` returns the offset of the literal suffix
+    /// (this will be at the end of the token if there is no suffix)
     fn number(&mut self, first_digit: char) -> (LiteralKind, u32) {
         debug_assert!('0' <= self.prev() && self.prev() <= '9');
         let mut base = Base::Decimal;

tests/ui/consts/custom-suffixes-exponent-like.rs

@@ -0,0 +1,10 @@
+const _A: f64 = 1em;
+    //~^ ERROR invalid suffix `em` for number literal
+const _B: f64 = 1e0m;
+    //~^ ERROR invalid suffix `m` for float literal
+const _C: f64 = 1e_______________0m;
+    //~^ ERROR invalid suffix `m` for float literal
+const _D: f64 = 1e_______________m;
+    //~^ ERROR invalid suffix `e_______________m` for number literal
+
+fn main() {}

tests/ui/consts/custom-suffixes-exponent-like.stderr

@@ -0,0 +1,34 @@
+error: invalid suffix `em` for number literal
+  --> $DIR/custom-suffixes-exponent-like.rs:1:17
+   |
+LL | const _A: f64 = 1em;
+   |                 ^^^ invalid suffix `em`
+   |
+   = help: the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)
+
+error: invalid suffix `m` for float literal
+  --> $DIR/custom-suffixes-exponent-like.rs:3:17
+   |
+LL | const _B: f64 = 1e0m;
+   |                 ^^^^ invalid suffix `m`
+   |
+   = help: valid suffixes are `f32` and `f64`
+
+error: invalid suffix `m` for float literal
+  --> $DIR/custom-suffixes-exponent-like.rs:5:17
+   |
+LL | const _C: f64 = 1e_______________0m;
+   |                 ^^^^^^^^^^^^^^^^^^^ invalid suffix `m`
+   |
+   = help: valid suffixes are `f32` and `f64`
+
+error: invalid suffix `e_______________m` for number literal
+  --> $DIR/custom-suffixes-exponent-like.rs:7:17
+   |
+LL | const _D: f64 = 1e_______________m;
+   |                 ^^^^^^^^^^^^^^^^^^ invalid suffix `e_______________m`
+   |
+   = help: the suffix must be one of the numeric types (`u32`, `isize`, `f32`, etc.)
+
+error: aborting due to 4 previous errors
+

tests/ui/consts/custom-suffixes.rs

@@ -0,0 +1,20 @@
+//@ run-pass
+
+// This tests different kinds of valid suffixes.
+
+fn main() {
+    const _A: f64 = 1.;
+    const _B: f64 = 1f64;
+    const _C: f64 = 1.0f64;
+    const _D: f64 = 1e6;
+    const _E: f64 = 1e-6;
+    const _F: f64 = 1.0e-6;
+    const _G: f64 = 1.0e06;
+    const _H: f64 = 1.0e+6;
+    const _I: f64 = 1.0e-6;
+    // these ones are perhaps more suprising.
+    const _J: f64 = 1.0e0________________________6;
+    const _K: f64 = 1.0e________________________6;
+    const _L: f64 = 1.0e+________________________6;
+    const _M: f64 = 1.0e-________________________6;
+}