3 files changed, 376 insertions, 1 deletions

diff --git a/crates/ide/src/completion/complete_postfix.rs b/crates/ide/src/completion/complete_postfix.rs
index 26a5af5b9..73a5f1439 100644
--- a/crates/ide/src/completion/complete_postfix.rs
+++ b/crates/ide/src/completion/complete_postfix.rs
@@ -6,6 +6,7 @@ use syntax::{
 };
 use text_edit::TextEdit;
 
+use self::format_like::add_format_like_completions;
 use crate::{
     completion::{
         completion_config::SnippetCap,
@@ -15,6 +16,8 @@ use crate::{
     CompletionItem, CompletionItemKind,
 };
 
+mod format_like;
+
 pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
     if !ctx.config.enable_postfix_completions {
         return;
@@ -207,6 +210,10 @@ pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
         &format!("${{1}}({})", receiver_text),
     )
     .add_to(acc);
+
+    if ctx.is_string_literal {
+        add_format_like_completions(acc, ctx, &dot_receiver, cap, &receiver_text);
+    }
 }
 
 fn get_receiver_text(receiver: &ast::Expr, receiver_is_ambiguous_float_literal: bool) -> String {
@@ -392,4 +399,53 @@ fn main() {
         check_edit("dbg", r#"fn main() { &&42.<|> }"#, r#"fn main() { dbg!(&&42) }"#);
         check_edit("refm", r#"fn main() { &&42.<|> }"#, r#"fn main() { &&&mut 42 }"#);
     }
+
+    #[test]
+    fn postfix_completion_for_format_like_strings() {
+        check_edit(
+            "fmt",
+            r#"fn main() { "{some_var:?}".<|> }"#,
+            r#"fn main() { format!("{:?}", some_var) }"#,
+        );
+        check_edit(
+            "panic",
+            r#"fn main() { "Panic with {a}".<|> }"#,
+            r#"fn main() { panic!("Panic with {}", a) }"#,
+        );
+        check_edit(
+            "println",
+            r#"fn main() { "{ 2+2 } { SomeStruct { val: 1, other: 32 } :?}".<|> }"#,
+            r#"fn main() { println!("{} {:?}", 2+2, SomeStruct { val: 1, other: 32 }) }"#,
+        );
+        check_edit(
+            "loge",
+            r#"fn main() { "{2+2}".<|> }"#,
+            r#"fn main() { log::error!("{}", 2+2) }"#,
+        );
+        check_edit(
+            "logt",
+            r#"fn main() { "{2+2}".<|> }"#,
+            r#"fn main() { log::trace!("{}", 2+2) }"#,
+        );
+        check_edit(
+            "logd",
+            r#"fn main() { "{2+2}".<|> }"#,
+            r#"fn main() { log::debug!("{}", 2+2) }"#,
+        );
+        check_edit(
+            "logi",
+            r#"fn main() { "{2+2}".<|> }"#,
+            r#"fn main() { log::info!("{}", 2+2) }"#,
+        );
+        check_edit(
+            "logw",
+            r#"fn main() { "{2+2}".<|> }"#,
+            r#"fn main() { log::warn!("{}", 2+2) }"#,
+        );
+        check_edit(
+            "loge",
+            r#"fn main() { "{2+2}".<|> }"#,
+            r#"fn main() { log::error!("{}", 2+2) }"#,
+        );
+    }
 }
diff --git a/crates/ide/src/completion/complete_postfix/format_like.rs b/crates/ide/src/completion/complete_postfix/format_like.rs
new file mode 100644
index 000000000..93211a35f
--- /dev/null
+++ b/crates/ide/src/completion/complete_postfix/format_like.rs
@@ -0,0 +1,310 @@
+//! Postfix completion for `format`-like strings.
+//!
+//! `"Result {result} is {2 + 2}"` is expanded to the `"Result {} is {}", result, 2 + 2`.
+//!
+//! The following postfix snippets are available:
+//!
+//! - `format` -> `format!(...)`
+//! - `println` -> `println!(...)`
+//! - `log`:
+//!   + `logd` -> `log::debug!(...)`
+//!   + `logt` -> `log::trace!(...)`
+//!   + `logi` -> `log::info!(...)`
+//!   + `logw` -> `log::warn!(...)`
+//!   + `loge` -> `log::error!(...)`
+
+use super::postfix_snippet;
+use crate::completion::{
+    completion_config::SnippetCap, completion_context::CompletionContext,
+    completion_item::Completions,
+};
+use syntax::ast;
+
+pub(super) fn add_format_like_completions(
+    acc: &mut Completions,
+    ctx: &CompletionContext,
+    dot_receiver: &ast::Expr,
+    cap: SnippetCap,
+    receiver_text: &str,
+) {
+    assert!(receiver_text.len() >= 2);
+    let input = &receiver_text[1..receiver_text.len() - 1];
+
+    let mut parser = FormatStrParser::new(input);
+
+    if parser.parse().is_ok() {
+        for kind in PostfixKind::all_suggestions() {
+            let snippet = parser.into_suggestion(*kind);
+            let (label, detail) = kind.into_description();
+
+            postfix_snippet(ctx, cap, &dot_receiver, label, detail, &snippet).add_to(acc);
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct FormatStrParser {
+    input: String,
+    output: String,
+    extracted_expressions: Vec<String>,
+    state: State,
+    parsed: bool,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum PostfixKind {
+    Format,
+    Panic,
+    Println,
+    LogDebug,
+    LogTrace,
+    LogInfo,
+    LogWarn,
+    LogError,
+}
+
+impl PostfixKind {
+    pub fn all_suggestions() -> &'static [PostfixKind] {
+        &[
+            Self::Format,
+            Self::Panic,
+            Self::Println,
+            Self::LogDebug,
+            Self::LogTrace,
+            Self::LogInfo,
+            Self::LogWarn,
+            Self::LogError,
+        ]
+    }
+
+    pub fn into_description(self) -> (&'static str, &'static str) {
+        match self {
+            Self::Format => ("fmt", "format!"),
+            Self::Panic => ("panic", "panic!"),
+            Self::Println => ("println", "println!"),
+            Self::LogDebug => ("logd", "log::debug!"),
+            Self::LogTrace => ("logt", "log::trace!"),
+            Self::LogInfo => ("logi", "log::info!"),
+            Self::LogWarn => ("logw", "log::warn!"),
+            Self::LogError => ("loge", "log::error!"),
+        }
+    }
+
+    pub fn into_macro_name(self) -> &'static str {
+        match self {
+            Self::Format => "format!",
+            Self::Panic => "panic!",
+            Self::Println => "println!",
+            Self::LogDebug => "log::debug!",
+            Self::LogTrace => "log::trace!",
+            Self::LogInfo => "log::info!",
+            Self::LogWarn => "log::warn!",
+            Self::LogError => "log::error!",
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+enum State {
+    NotExpr,
+    MaybeExpr,
+    Expr,
+    MaybeIncorrect,
+    FormatOpts,
+}
+
+impl FormatStrParser {
+    pub fn new(input: impl Into<String>) -> Self {
+        Self {
+            input: input.into(),
+            output: String::new(),
+            extracted_expressions: Vec::new(),
+            state: State::NotExpr,
+            parsed: false,
+        }
+    }
+
+    pub fn parse(&mut self) -> Result<(), ()> {
+        let mut current_expr = String::new();
+
+        let mut placeholders_count = 0;
+
+        // Count of open braces inside of an expression.
+        // We assume that user knows what they're doing, thus we treat it like a correct pattern, e.g.
+        // "{MyStruct { val_a: 0, val_b: 1 }}".
+        let mut inexpr_open_count = 0;
+
+        for chr in self.input.chars() {
+            match (self.state, chr) {
+                (State::NotExpr, '{') => {
+                    self.output.push(chr);
+                    self.state = State::MaybeExpr;
+                }
+                (State::NotExpr, '}') => {
+                    self.output.push(chr);
+                    self.state = State::MaybeIncorrect;
+                }
+                (State::NotExpr, _) => {
+                    self.output.push(chr);
+                }
+                (State::MaybeIncorrect, '}') => {
+                    // It's okay, we met "}}".
+                    self.output.push(chr);
+                    self.state = State::NotExpr;
+                }
+                (State::MaybeIncorrect, _) => {
+                    // Error in the string.
+                    return Err(());
+                }
+                (State::MaybeExpr, '{') => {
+                    self.output.push(chr);
+                    self.state = State::NotExpr;
+                }
+                (State::MaybeExpr, '}') => {
+                    // This is an empty sequence '{}'. Replace it with placeholder.
+                    self.output.push(chr);
+                    self.extracted_expressions.push(format!("${}", placeholders_count));
+                    placeholders_count += 1;
+                    self.state = State::NotExpr;
+                }
+                (State::MaybeExpr, _) => {
+                    current_expr.push(chr);
+                    self.state = State::Expr;
+                }
+                (State::Expr, '}') => {
+                    if inexpr_open_count == 0 {
+                        self.output.push(chr);
+                        self.extracted_expressions.push(current_expr.trim().into());
+                        current_expr = String::new();
+                        self.state = State::NotExpr;
+                    } else {
+                        // We're closing one brace met before inside of the expression.
+                        current_expr.push(chr);
+                        inexpr_open_count -= 1;
+                    }
+                }
+                (State::Expr, ':') => {
+                    if inexpr_open_count == 0 {
+                        // We're outside of braces, thus assume that it's a specifier, like "{Some(value):?}"
+                        self.output.push(chr);
+                        self.extracted_expressions.push(current_expr.trim().into());
+                        current_expr = String::new();
+                        self.state = State::FormatOpts;
+                    } else {
+                        // We're inside of braced expression, assume that it's a struct field name/value delimeter.
+                        current_expr.push(chr);
+                    }
+                }
+                (State::Expr, '{') => {
+                    current_expr.push(chr);
+                    inexpr_open_count += 1;
+                }
+                (State::Expr, _) => {
+                    current_expr.push(chr);
+                }
+                (State::FormatOpts, '}') => {
+                    self.output.push(chr);
+                    self.state = State::NotExpr;
+                }
+                (State::FormatOpts, _) => {
+                    self.output.push(chr);
+                }
+            }
+        }
+
+        if self.state != State::NotExpr {
+            return Err(());
+        }
+
+        self.parsed = true;
+        Ok(())
+    }
+
+    pub fn into_suggestion(&self, kind: PostfixKind) -> String {
+        assert!(self.parsed, "Attempt to get a suggestion from not parsed expression");
+
+        let mut output = format!(r#"{}("{}""#, kind.into_macro_name(), self.output);
+        for expr in &self.extracted_expressions {
+            output += ", ";
+            output += expr;
+        }
+        output.push(')');
+
+        output
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn format_str_parser() {
+        let test_vector = &[
+            ("no expressions", Some(("no expressions", vec![]))),
+            ("{expr} is {2 + 2}", Some(("{} is {}", vec!["expr", "2 + 2"]))),
+            ("{expr:?}", Some(("{:?}", vec!["expr"]))),
+            ("{malformed", None),
+            ("malformed}", None),
+            ("{{correct", Some(("{{correct", vec![]))),
+            ("correct}}", Some(("correct}}", vec![]))),
+            ("{correct}}}", Some(("{}}}", vec!["correct"]))),
+            ("{correct}}}}}", Some(("{}}}}}", vec!["correct"]))),
+            ("{incorrect}}", None),
+            ("placeholders {} {}", Some(("placeholders {} {}", vec!["$0", "$1"]))),
+            ("mixed {} {2 + 2} {}", Some(("mixed {} {} {}", vec!["$0", "2 + 2", "$1"]))),
+            (
+                "{SomeStruct { val_a: 0, val_b: 1 }}",
+                Some(("{}", vec!["SomeStruct { val_a: 0, val_b: 1 }"])),
+            ),
+            ("{expr:?} is {2.32f64:.5}", Some(("{:?} is {:.5}", vec!["expr", "2.32f64"]))),
+            (
+                "{SomeStruct { val_a: 0, val_b: 1 }:?}",
+                Some(("{:?}", vec!["SomeStruct { val_a: 0, val_b: 1 }"])),
+            ),
+            ("{     2 + 2        }", Some(("{}", vec!["2 + 2"]))),
+        ];
+
+        for (input, output) in test_vector {
+            let mut parser = FormatStrParser::new(*input);
+            let outcome = parser.parse();
+
+            if let Some((result_str, result_args)) = output {
+                assert!(
+                    outcome.is_ok(),
+                    "Outcome is error for input: {}, but the expected outcome is {:?}",
+                    input,
+                    output
+                );
+                assert_eq!(parser.output, *result_str);
+                assert_eq!(&parser.extracted_expressions, result_args);
+            } else {
+                assert!(
+                    outcome.is_err(),
+                    "Outcome is OK for input: {}, but the expected outcome is error",
+                    input
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn test_into_suggestion() {
+        let test_vector = &[
+            (PostfixKind::Println, "{}", r#"println!("{}", $0)"#),
+            (
+                PostfixKind::LogInfo,
+                "{} {expr} {} {2 + 2}",
+                r#"log::info!("{} {} {} {}", $0, expr, $1, 2 + 2)"#,
+            ),
+            (PostfixKind::Format, "{expr:?}", r#"format!("{:?}", expr)"#),
+        ];
+
+        for (kind, input, output) in test_vector {
+            let mut parser = FormatStrParser::new(*input);
+            parser.parse().expect("Parsing must succeed");
+
+            assert_eq!(&parser.into_suggestion(*kind), output);
+        }
+    }
+}
diff --git a/crates/ide/src/completion/completion_context.rs b/crates/ide/src/completion/completion_context.rs
index 671b13328..842d1987c 100644
--- a/crates/ide/src/completion/completion_context.rs
+++ b/crates/ide/src/completion/completion_context.rs
@@ -74,6 +74,8 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) is_pattern_call: bool,
     /// If this is a macro call, i.e. the () are already there.
     pub(super) is_macro_call: bool,
+    /// If this is a string literal, like "lorem ipsum".
+    pub(super) is_string_literal: bool,
     pub(super) is_path_type: bool,
     pub(super) has_type_args: bool,
     pub(super) attribute_under_caret: Option<ast::Attr>,
@@ -156,6 +158,7 @@ impl<'a> CompletionContext<'a> {
             is_call: false,
             is_pattern_call: false,
             is_macro_call: false,
+            is_string_literal: false,
             is_path_type: false,
             has_type_args: false,
             dot_receiver_is_ambiguous_float_literal: false,
@@ -469,7 +472,13 @@ impl<'a> CompletionContext<'a> {
                     }
                 } else {
                     false
-                }
+                };
+
+            self.is_string_literal = if let Some(ast::Expr::Literal(l)) = &self.dot_receiver {
+                matches!(l.kind(), ast::LiteralKind::String { .. })
+            } else {
+                false
+            };
         }
         if let Some(method_call_expr) = ast::MethodCallExpr::cast(parent) {
             // As above