String formatting: support padding, alignment and precision

godot-core/src/builtin/string/gstring.rs

@@ -13,7 +13,7 @@ use godot_ffi as sys;
 use sys::types::OpaqueString;
 use sys::{ffi_methods, interface_fn, GodotFfi};
 
-use crate::builtin::string::Encoding;
+use crate::builtin::string::{pad_if_needed, Encoding};
 use crate::builtin::{inner, NodePath, StringName, Variant};
 use crate::meta::error::StringError;
 use crate::meta::AsArg;
@@ -298,11 +298,13 @@ impl_shared_string_api! {
 
 impl fmt::Display for GString {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        for ch in self.chars() {
-            f.write_char(*ch)?;
-        }
+        pad_if_needed(f, |f| {
+            for ch in self.chars() {
+                f.write_char(*ch)?;
+            }
 
-        Ok(())
+            Ok(())
+        })
     }
 }
 

godot-core/src/builtin/string/mod.rs

@@ -155,3 +155,48 @@ fn found_to_option(index: i64) -> Option<usize> {
         Some(index_usize)
     }
 }
+
+// ----------------------------------------------------------------------------------------------------------------------------------------------
+// Padding, alignment and precision support
+
+// Used by sub-modules of this module.
+use standard_fmt::pad_if_needed;
+
+mod standard_fmt {
+    use std::fmt;
+    use std::fmt::Write;
+
+    pub fn pad_if_needed<F>(f: &mut fmt::Formatter<'_>, display_impl: F) -> fmt::Result
+    where
+        F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,
+    {
+        let needs_format = f.width().is_some() || f.precision().is_some() || f.align().is_some();
+
+        // Early exit if no custom formatting is needed.
+        if !needs_format {
+            return display_impl(f);
+        }
+
+        let ic = FmtInterceptor { display_impl };
+
+        let mut local_str = String::new();
+        write!(&mut local_str, "{ic}")?;
+        f.pad(&local_str)
+    }
+
+    struct FmtInterceptor<F>
+    where
+        F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,
+    {
+        display_impl: F,
+    }
+
+    impl<F> fmt::Display for FmtInterceptor<F>
+    where
+        F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result,
+    {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            (self.display_impl)(f)
+        }
+    }
+}

godot-core/src/global/print.rs

@@ -50,6 +50,11 @@ macro_rules! inner_godot_msg {
 
 /// Pushes a warning message to Godot's built-in debugger and to the OS terminal.
 ///
+/// # See also
+/// [`godot_print!`](macro.godot_print.html) and [`godot_error!`](macro.godot_error.html).
+///
+/// Related to the utility function [`global::push_warning()`](crate::global::push_warning).
+///
 /// _Godot equivalent: [`@GlobalScope.push_warning()`](https://docs.godotengine.org/en/stable/classes/[email protected]#class-globalscope-method-push-warning)_.
 #[macro_export]
 macro_rules! godot_warn {
@@ -60,6 +65,12 @@ macro_rules! godot_warn {
 
 /// Pushes an error message to Godot's built-in debugger and to the OS terminal.
 ///
+/// # See also
+/// [`godot_print!`](macro.godot_print.html) and [`godot_warn!`](macro.godot_warn.html).
+/// For script errors (less relevant in Rust), use [`godot_script_error!`](macro.godot_script_error.html).
+///
+/// Related to the utility function [`global::push_error()`][crate::global::push_error].
+///
 /// _Godot equivalent: [`@GlobalScope.push_error()`](https://docs.godotengine.org/en/stable/classes/[email protected]#class-globalscope-method-push-error)_.
 #[macro_export]
 macro_rules! godot_error {
@@ -69,6 +80,13 @@ macro_rules! godot_error {
 }
 
 /// Logs a script error to Godot's built-in debugger and to the OS terminal.
+///
+/// This is rarely needed in Rust; script errors are typically emitted by the GDScript parser.
+///
+/// # See also
+/// [`godot_error!`](macro.godot_error.html) for a general error message.
+///
+///
 #[macro_export]
 macro_rules! godot_script_error {
     ($fmt:literal $(, $args:expr)* $(,)?) => {
@@ -78,6 +96,22 @@ macro_rules! godot_script_error {
 
 /// Prints to the Godot console.
 ///
+/// Automatically appends a newline character at the end of the message.
+///
+/// Used exactly like standard [`println!`]:
+/// ```no_run
+/// use godot::global::godot_print;
+///
+/// let version = 4;
+/// godot_print!("Hello, Godot {version}!");
+/// ```
+///
+/// # See also
+/// [`godot_print_rich!`](macro.godot_print_rich.html) for a slower alternative that supports BBCode, color and URL tags.
+/// To print Godot errors and warnings, use [`godot_error!`](macro.godot_error.html) and [`godot_warn!`](macro.godot_warn.html), respectively.
+///
+/// This uses the underlying [`global::print()`][crate::global::print] function, which takes a variable-length slice of variants.
+///
 /// _Godot equivalent: [`@GlobalScope.print()`](https://docs.godotengine.org/en/stable/classes/[email protected]#class-globalscope-method-print)_.
 #[macro_export]
 macro_rules! godot_print {
@@ -92,7 +126,7 @@ macro_rules! godot_print {
 
 /// Prints to the Godot console. Supports BBCode, color and URL tags.
 ///
-/// Slower than [`godot_print!`].
+/// Slower than [`godot_print!`](macro.godot_print_rich.html).
 ///
 /// _Godot equivalent: [`@GlobalScope.print_rich()`](https://docs.godotengine.org/en/stable/classes/[email protected]#class-globalscope-method-print-rich)_.
 #[macro_export]

itest/rust/src/builtin_tests/string/gstring_test.rs

@@ -279,6 +279,14 @@ crate::generate_string_bytes_and_cstr_tests!(
     ]
 );
 
+crate::generate_string_standard_fmt_tests!(
+    builtin: GString,
+    tests: [
+        gstring_display,
+        gstring_standard_pad,
+    ]
+);
+
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 // Helpers
 

itest/rust/src/builtin_tests/string/node_path_test.rs

@@ -31,6 +31,7 @@ fn node_path_conversion() {
 
     assert_eq!(string, back);
 }
+
 #[itest]
 fn node_path_equality() {
     let string = NodePath::from("some string");
@@ -126,3 +127,11 @@ fn node_path_get_subname() {
         assert_eq!(path.get_subname(2), "".into());
     })
 }
+
+crate::generate_string_standard_fmt_tests!(
+    builtin: NodePath,
+    tests: [
+        node_path_display,
+        node_path_standard_pad,
+    ]
+);

itest/rust/src/builtin_tests/string/string_name_test.rs

@@ -175,3 +175,11 @@ crate::generate_string_bytes_and_cstr_tests!(
         string_name_from_cstr_utf8,
     ]
 );
+
+crate::generate_string_standard_fmt_tests!(
+    builtin: StringName,
+    tests: [
+        string_name_display,
+        string_name_standard_pad,
+    ]
+);

itest/rust/src/builtin_tests/string/string_test_macros.rs

@@ -162,3 +162,35 @@ macro_rules! generate_string_bytes_and_cstr_tests {
         }
     };
 }
+
+// Tests padding with the standard formatter.
+#[macro_export]
+macro_rules! generate_string_standard_fmt_tests {
+    (
+        builtin: $T:ty,
+        tests: [
+            $display:ident,
+            $standard_pad:ident,
+        ]
+    ) => {
+        #[itest]
+        fn $display() {
+            let s = <$T>::from("abcd");
+
+            assert_eq!(format!("{s}"), "abcd");
+        }
+
+        #[itest]
+        fn $standard_pad() {
+            let s = <$T>::from("abcd");
+
+            // Padding with spaces + alignment.
+            assert_eq!(format!("{s:<6}"), "abcd  ");
+            assert_eq!(format!("{s:>6}"), "  abcd");
+
+            // Precision.
+            assert_eq!(format!("{s:.2}"), "ab");
+            assert_eq!(format!("{s:.3}"), "abc");
+        }
+    };
+}