Add parser for LSP snippet

4 files changed, 371 insertions, 0 deletions

diff --git a/Cargo.lock b/Cargo.lock
index affc6bd9..d069cf41 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1141,6 +1141,7 @@ dependencies = [
  "helix-loader",
  "log",
  "lsp-types",
+ "once_cell",
  "serde",
  "serde_json",
  "thiserror",
diff --git a/helix-lsp/Cargo.toml b/helix-lsp/Cargo.toml
index c1f09110..7c71fa9f 100644
--- a/helix-lsp/Cargo.toml
+++ b/helix-lsp/Cargo.toml
@@ -14,6 +14,7 @@ homepage = "https://helix-editor.com"
 [dependencies]
 helix-core = { version = "0.6", path = "../helix-core" }
 helix-loader = { version = "0.6", path = "../helix-loader" }
+helix-parsec = { version = "0.6", path = "../helix-parsec" }
 
 anyhow = "1.0"
 futures-executor = "0.3"
@@ -26,3 +27,4 @@ thiserror = "1.0"
 tokio = { version = "1.26", features = ["rt", "rt-multi-thread", "io-util", "io-std", "time", "process", "macros", "fs", "parking_lot", "sync"] }
 tokio-stream = "0.1.12"
 which = "4.4"
+once_cell = "1.15"
diff --git a/helix-lsp/src/lib.rs b/helix-lsp/src/lib.rs
index ca9d17ac..cce848ab 100644
--- a/helix-lsp/src/lib.rs
+++ b/helix-lsp/src/lib.rs
@@ -1,5 +1,6 @@
 mod client;
 pub mod jsonrpc;
+pub mod snippet;
 mod transport;
 
 pub use client::Client;
diff --git a/helix-lsp/src/snippet.rs b/helix-lsp/src/snippet.rs
new file mode 100644
index 00000000..529c3b97
--- /dev/null
+++ b/helix-lsp/src/snippet.rs
@@ -0,0 +1,367 @@
+use anyhow::{anyhow, Result};
+
+use crate::{util::lsp_pos_to_pos, OffsetEncoding};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum CaseChange {
+    Upcase,
+    Downcase,
+    Capitalize,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum FormatItem<'a> {
+    Text(&'a str),
+    Capture(usize),
+    CaseChange(usize, CaseChange),
+    Conditional(usize, Option<&'a str>, Option<&'a str>),
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Regex<'a> {
+    value: &'a str,
+    replacement: Vec<FormatItem<'a>>,
+    options: Option<&'a str>,
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum SnippetElement<'a> {
+    Tabstop {
+        tabstop: usize,
+    },
+    Placeholder {
+        tabstop: usize,
+        value: Box<SnippetElement<'a>>,
+    },
+    Choice {
+        tabstop: usize,
+        choices: Vec<&'a str>,
+    },
+    Variable {
+        name: &'a str,
+        default: Option<&'a str>,
+        regex: Option<Regex<'a>>,
+    },
+    Text(&'a str),
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct Snippet<'a> {
+    elements: Vec<SnippetElement<'a>>,
+}
+
+pub fn parse<'a>(s: &'a str) -> Result<Snippet<'a>> {
+    parser::parse(s).map_err(|rest| anyhow!("Failed to parse snippet. Remaining input: {}", rest))
+}
+
+mod parser {
+    use helix_core::regex;
+    use once_cell::sync::Lazy;
+
+    use helix_parsec::*;
+
+    use super::{CaseChange, FormatItem, Regex, Snippet, SnippetElement};
+
+    /*
+    https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#snippet_syntax
+
+        any         ::= tabstop | placeholder | choice | variable | text
+        tabstop     ::= '$' int | '${' int '}'
+        placeholder ::= '${' int ':' any '}'
+        choice      ::= '${' int '|' text (',' text)* '|}'
+        variable    ::= '$' var | '${' var }'
+                        | '${' var ':' any '}'
+                        | '${' var '/' regex '/' (format | text)+ '/' options '}'
+        format      ::= '$' int | '${' int '}'
+                        | '${' int ':' '/upcase' | '/downcase' | '/capitalize' '}'
+                        | '${' int ':+' if '}'
+                        | '${' int ':?' if ':' else '}'
+                        | '${' int ':-' else '}' | '${' int ':' else '}'
+        regex       ::= Regular Expression value (ctor-string)
+        options     ::= Regular Expression option (ctor-options)
+        var         ::= [_a-zA-Z] [_a-zA-Z0-9]*
+        int         ::= [0-9]+
+        text        ::= .*
+        if          ::= text
+        else        ::= text
+    */
+
+    static DIGIT: Lazy<regex::Regex> = Lazy::new(|| regex::Regex::new(r"^[0-9]+").unwrap());
+    static VARIABLE: Lazy<regex::Regex> =
+        Lazy::new(|| regex::Regex::new(r"^[_a-zA-Z][_a-zA-Z0-9]*").unwrap());
+    static TEXT: Lazy<regex::Regex> = Lazy::new(|| regex::Regex::new(r"^[^\$]+").unwrap());
+
+    fn var<'a>() -> impl Parser<'a, Output = &'a str> {
+        pattern(&VARIABLE)
+    }
+
+    fn digit<'a>() -> impl Parser<'a, Output = usize> {
+        filter_map(pattern(&DIGIT), |s| s.parse().ok())
+    }
+
+    fn case_change<'a>() -> impl Parser<'a, Output = CaseChange> {
+        use CaseChange::*;
+
+        choice!(
+            map("upcase", |_| Upcase),
+            map("downcase", |_| Downcase),
+            map("capitalize", |_| Capitalize),
+        )
+    }
+
+    fn format<'a>() -> impl Parser<'a, Output = FormatItem<'a>> {
+        use FormatItem::*;
+
+        choice!(
+            // '$' int
+            map(right("$", digit()), Capture),
+            // '${' int '}'
+            map(seq!("${", digit(), "}"), |seq| Capture(seq.1)),
+            // '${' int ':' '/upcase' | '/downcase' | '/capitalize' '}'
+            map(seq!("${", digit(), ":/", case_change(), "}"), |seq| {
+                CaseChange(seq.1, seq.3)
+            }),
+            // '${' int ':+' if '}'
+            map(
+                seq!("${", digit(), ":+", take_until(|c| c == '}'), "}"),
+                |seq| { Conditional(seq.1, Some(seq.3), None) }
+            ),
+            // '${' int ':?' if ':' else '}'
+            map(
+                seq!(
+                    "${",
+                    digit(),
+                    ":?",
+                    take_until(|c| c == ':'),
+                    ":",
+                    take_until(|c| c == '}'),
+                    "}"
+                ),
+                |seq| { Conditional(seq.1, Some(seq.3), Some(seq.5)) }
+            ),
+            // '${' int ':-' else '}' | '${' int ':' else '}'
+            map(
+                seq!(
+                    "${",
+                    digit(),
+                    ":",
+                    optional("-"),
+                    take_until(|c| c == '}'),
+                    "}"
+                ),
+                |seq| { Conditional(seq.1, None, Some(seq.4)) }
+            ),
+            // Any text
+            map(pattern(&TEXT), Text),
+        )
+    }
+
+    fn regex<'a>() -> impl Parser<'a, Output = Regex<'a>> {
+        let replacement = reparse_as(take_until(|c| c == '/'), one_or_more(format()));
+
+        map(
+            seq!(
+                "/",
+                take_until(|c| c == '/'),
+                "/",
+                replacement,
+                "/",
+                optional(take_until(|c| c == '}')),
+            ),
+            |(_, value, _, replacement, _, options)| Regex {
+                value,
+                replacement,
+                options,
+            },
+        )
+    }
+
+    fn tabstop<'a>() -> impl Parser<'a, Output = SnippetElement<'a>> {
+        map(
+            or(
+                right("$", digit()),
+                map(seq!("${", digit(), "}"), |values| values.1),
+            ),
+            |digit| SnippetElement::Tabstop { tabstop: digit },
+        )
+    }
+
+    fn placeholder<'a>() -> impl Parser<'a, Output = SnippetElement<'a>> {
+        // TODO: why doesn't parse_as work?
+        // let value = reparse_as(take_until(|c| c == '}'), anything());
+        let value = filter_map(take_until(|c| c == '}'), |s| {
+            anything().parse(s).map(|parse_result| parse_result.1).ok()
+        });
+
+        map(seq!("${", digit(), ":", value, "}"), |seq| {
+            SnippetElement::Placeholder {
+                tabstop: seq.1,
+                value: Box::new(seq.3),
+            }
+        })
+    }
+
+    fn choice<'a>() -> impl Parser<'a, Output = SnippetElement<'a>> {
+        map(
+            seq!(
+                "${",
+                digit(),
+                "|",
+                sep(take_until(|c| c == ',' || c == '|'), ","),
+                "|}",
+            ),
+            |seq| SnippetElement::Choice {
+                tabstop: seq.1,
+                choices: seq.3,
+            },
+        )
+    }
+
+    fn variable<'a>() -> impl Parser<'a, Output = SnippetElement<'a>> {
+        choice!(
+            // $var
+            map(right("$", var()), |name| SnippetElement::Variable {
+                name,
+                default: None,
+                regex: None,
+            }),
+            // ${var:default}
+            map(
+                seq!("${", var(), ":", take_until(|c| c == '}'), "}",),
+                |values| SnippetElement::Variable {
+                    name: values.1,
+                    default: Some(values.3),
+                    regex: None,
+                }
+            ),
+            // ${var/value/format/options}
+            map(seq!("${", var(), regex(), "}"), |values| {
+                SnippetElement::Variable {
+                    name: values.1,
+                    default: None,
+                    regex: Some(values.2),
+                }
+            }),
+        )
+    }
+
+    fn text<'a>() -> impl Parser<'a, Output = SnippetElement<'a>> {
+        map(pattern(&TEXT), SnippetElement::Text)
+    }
+
+    fn anything<'a>() -> impl Parser<'a, Output = SnippetElement<'a>> {
+        choice!(tabstop(), placeholder(), choice(), variable(), text())
+    }
+
+    fn snippet<'a>() -> impl Parser<'a, Output = Snippet<'a>> {
+        map(one_or_more(anything()), |parts| Snippet { elements: parts })
+    }
+
+    pub fn parse(s: &str) -> Result<Snippet, &str> {
+        snippet().parse(s).map(|(_input, elements)| elements)
+    }
+
+    #[cfg(test)]
+    mod test {
+        use super::SnippetElement::*;
+        use super::*;
+
+        #[test]
+        fn empty_string_is_error() {
+            assert_eq!(Err(""), parse(""));
+        }
+
+        #[test]
+        fn parse_placeholders_in_function_call() {
+            assert_eq!(
+                Ok(Snippet {
+                    elements: vec![
+                        Text("match("),
+                        Placeholder {
+                            tabstop: 1,
+                            value: Box::new(Text("Arg1")),
+                        },
+                        Text(")")
+                    ]
+                }),
+                parse("match(${1:Arg1})")
+            )
+        }
+
+        #[test]
+        fn parse_placeholders_in_statement() {
+            assert_eq!(
+                Ok(Snippet {
+                    elements: vec![
+                        Text("local "),
+                        Placeholder {
+                            tabstop: 1,
+                            value: Box::new(Text("var")),
+                        },
+                        Text(" = "),
+                        Placeholder {
+                            tabstop: 1,
+                            value: Box::new(Text("value")),
+                        },
+                    ]
+                }),
+                parse("local ${1:var} = ${1:value}")
+            )
+        }
+
+        #[test]
+        fn parse_all() {
+            assert_eq!(
+                Ok(Snippet {
+                    elements: vec![
+                        Text("hello "),
+                        Tabstop { tabstop: 1 },
+                        Tabstop { tabstop: 2 },
+                        Text(" "),
+                        Choice {
+                            tabstop: 1,
+                            choices: vec!["one", "two", "three"]
+                        },
+                        Text(" "),
+                        Variable {
+                            name: "name",
+                            default: Some("foo"),
+                            regex: None
+                        },
+                        Text(" "),
+                        Variable {
+                            name: "var",
+                            default: None,
+                            regex: None
+                        },
+                        Text(" "),
+                        Variable {
+                            name: "TM",
+                            default: None,
+                            regex: None
+                        },
+                    ]
+                }),
+                parse("hello $1${2} ${1|one,two,three|} ${name:foo} $var $TM")
+            );
+        }
+
+        #[test]
+        fn regex_capture_replace() {
+            assert_eq!(
+                Ok(Snippet {
+                    elements: vec![Variable {
+                        name: "TM_FILENAME",
+                        default: None,
+                        regex: Some(Regex {
+                            value: "(.*).+$",
+                            replacement: vec![FormatItem::Capture(1)],
+                            options: None,
+                        }),
+                    }]
+                }),
+                parse("${TM_FILENAME/(.*).+$/$1/}")
+            );
+        }
+    }
+}