dbg macro: align line number to 4 digits

Author: hellow554

src/libstd/macros.rs

@@ -221,7 +221,7 @@ macro_rules! eprintln {
 /// ```rust
 /// let a = 2;
 /// let b = dbg!(a * 2) + 1;
-/// //      ^-- prints: [src/main.rs:2] a * 2 = 4
+/// //      ^-- prints: [src/main.rs:0002] a * 2 = 4
 /// assert_eq!(b, 5);
 /// ```
 ///
@@ -267,7 +267,7 @@ macro_rules! eprintln {
 /// This prints to [stderr]:
 ///
 /// ```text,ignore
-/// [src/main.rs:4] n.checked_sub(4) = None
+/// [src/main.rs:0004] n.checked_sub(4) = None
 /// ```
 ///
 /// Naive factorial implementation:
@@ -287,15 +287,15 @@ macro_rules! eprintln {
 /// This prints to [stderr]:
 ///
 /// ```text,ignore
-/// [src/main.rs:3] n <= 1 = false
-/// [src/main.rs:3] n <= 1 = false
-/// [src/main.rs:3] n <= 1 = false
-/// [src/main.rs:3] n <= 1 = true
-/// [src/main.rs:4] 1 = 1
-/// [src/main.rs:5] n * factorial(n - 1) = 2
-/// [src/main.rs:5] n * factorial(n - 1) = 6
-/// [src/main.rs:5] n * factorial(n - 1) = 24
-/// [src/main.rs:11] factorial(4) = 24
+/// [src/main.rs:0003] n <= 1 = false
+/// [src/main.rs:0003] n <= 1 = false
+/// [src/main.rs:0003] n <= 1 = false
+/// [src/main.rs:0003] n <= 1 = true
+/// [src/main.rs:0004] 1 = 1
+/// [src/main.rs:0005] n * factorial(n - 1) = 2
+/// [src/main.rs:0005] n * factorial(n - 1) = 6
+/// [src/main.rs:0005] n * factorial(n - 1) = 24
+/// [src/main.rs:0011] factorial(4) = 24
 /// ```
 ///
 /// The `dbg!(..)` macro moves the input:
@@ -319,7 +319,7 @@ macro_rules! dbg {
         // of temporaries - https://stackoverflow.com/a/48732525/1063961
         match $val {
             tmp => {
-                eprintln!("[{}:{}] {} = {:#?}",
+                eprintln!("[{}:{:04}] {} = {:#?}",
                     file!(), line!(), stringify!($val), &tmp);
                 tmp
             }

src/test/ui/rfc-2361-dbg-macro/dbg-macro-expected-behavior.rs

@@ -55,31 +55,31 @@ fn test() {
 
 fn validate_stderr(stderr: Vec<String>) {
     assert_eq!(stderr, &[
-        ":21] Unit = Unit",
+        ":0021] Unit = Unit",
 
-        ":22] a = Unit",
+        ":0022] a = Unit",
 
-        ":28] Point{x: 42, y: 24,} = Point {",
+        ":0028] Point{x: 42, y: 24,} = Point {",
         "    x: 42,",
         "    y: 24",
         "}",
 
-        ":29] b = Point {",
+        ":0029] b = Point {",
         "    x: 42,",
         "    y: 24",
         "}",
 
-        ":38] &a = NoCopy(",
+        ":0038] &a = NoCopy(",
         "    1337",
         ")",
 
-        ":38] dbg!(& a) = NoCopy(",
+        ":0038] dbg!(& a) = NoCopy(",
         "    1337",
         ")",
-        ":43] f(&42) = 42",
+        ":0043] f(&42) = 42",
 
         "before",
-        ":48] { foo += 1; eprintln!(\"before\"); 7331 } = 7331",
+        ":0048] { foo += 1; eprintln!(\"before\"); 7331 } = 7331",
     ]);
 }