templater: add similarity hint to no such method/keyword errors

The translation from method error to keyword error can go wrong if the context
object had n-ary methods (n > 0), which isn't the case as of now. For
simplicity, arguments error is mapped to "self.<name>(..)" suggestion.

Local variables and "self" could be merged without using extra method, but
we'll need extend_*_candidates() to merge in symbol/function aliases anyway.

cli/Cargo.toml

@@ -63,6 +63,7 @@ rpassword = { workspace = true }
 scm-record = { workspace = true }
 serde = { workspace = true }
 slab = { workspace = true }
+strsim = { workspace = true }
 tempfile = { workspace = true }
 textwrap = { workspace = true }
 thiserror = { workspace = true }

cli/src/cli_util.rs

@@ -86,7 +86,7 @@ use crate::git_util::{
     is_colocated_git_workspace, print_failed_git_export, print_git_import_stats,
 };
 use crate::merge_tools::{ConflictResolveError, DiffEditError, DiffGenerateError};
-use crate::template_parser::{TemplateAliasesMap, TemplateParseError};
+use crate::template_parser::{TemplateAliasesMap, TemplateParseError, TemplateParseErrorKind};
 use crate::templater::Template;
 use crate::ui::{ColorChoice, Ui};
 use crate::{commit_templater, text_util};
@@ -453,8 +453,18 @@ impl From<RevsetResolutionError> for CommandError {
 
 impl From<TemplateParseError> for CommandError {
     fn from(err: TemplateParseError) -> Self {
-        let message = iter::successors(Some(&err), |e| e.origin()).join("\n");
-        user_error(format!("Failed to parse template: {message}"))
+        let err_chain = iter::successors(Some(&err), |e| e.origin());
+        let message = err_chain.clone().join("\n");
+        // Only for the bottom error, which is usually the root cause
+        let hint = match err_chain.last().unwrap().kind() {
+            TemplateParseErrorKind::NoSuchKeyword { candidates, .. }
+            | TemplateParseErrorKind::NoSuchFunction { candidates, .. }
+            | TemplateParseErrorKind::NoSuchMethod { candidates, .. } => {
+                format_similarity_hint(candidates)
+            }
+            _ => None,
+        };
+        user_error_with_hint_opt(format!("Failed to parse template: {message}"), hint)
     }
 }
 

cli/src/template_builder.rs

@@ -19,7 +19,7 @@ use jj_lib::backend::{Signature, Timestamp};
 
 use crate::template_parser::{
     self, BinaryOp, ExpressionKind, ExpressionNode, FunctionCallNode, MethodCallNode,
-    TemplateParseError, TemplateParseResult, UnaryOp,
+    TemplateParseError, TemplateParseErrorKind, TemplateParseResult, UnaryOp,
 };
 use crate::templater::{
     ConcatTemplate, ConditionalTemplate, IntoTemplate, LabelTemplate, ListPropertyTemplate,
@@ -389,12 +389,27 @@ fn build_keyword<'a, L: TemplateLanguage<'a>>(
         args: vec![],
         args_span: name_span.end_pos().span(&name_span.end_pos()),
     };
-    let property = language
-        .build_method(build_ctx, self_property, &function)
-        // Since keyword is a 0-ary method, any argument-related errors mean
-        // there's no such keyword.
-        .map_err(|_| TemplateParseError::no_such_keyword(name, name_span))?;
-    Ok(Expression::with_label(property, name))
+    match language.build_method(build_ctx, self_property, &function) {
+        Ok(property) => Ok(Expression::with_label(property, name)),
+        Err(err) => {
+            let kind = if let TemplateParseErrorKind::NoSuchMethod { candidates, .. } = err.kind() {
+                TemplateParseErrorKind::NoSuchKeyword {
+                    name: name.to_owned(),
+                    // TODO: filter methods by arity?
+                    candidates: candidates.clone(),
+                }
+            } else {
+                // Since keyword is a 0-ary method, any argument-related errors
+                // mean there's no such keyword.
+                TemplateParseErrorKind::NoSuchKeyword {
+                    name: name.to_owned(),
+                    // TODO: might be better to phrase the error differently
+                    candidates: vec![format!("self.{name}(..)")],
+                }
+            };
+            Err(TemplateParseError::with_span(kind, name_span))
+        }
+    }
 }
 
 fn build_unary_operation<'a, L: TemplateLanguage<'a>>(
@@ -923,7 +938,12 @@ pub fn build_expression<'a, L: TemplateLanguage<'a>>(
                 // "self" is a special variable, so don't label it
                 Ok(Expression::unlabeled(language.build_self()))
             } else {
-                build_keyword(language, build_ctx, name, node.span)
+                build_keyword(language, build_ctx, name, node.span).map_err(|err| {
+                    err.extend_keyword_candidates(itertools::chain(
+                        build_ctx.local_variables.keys().copied(),
+                        ["self"],
+                    ))
+                })
             }
         }
         ExpressionKind::Boolean(value) => {

cli/src/template_parser.rs

@@ -14,7 +14,7 @@
 
 use std::collections::HashMap;
 use std::num::ParseIntError;
-use std::{error, fmt, iter};
+use std::{error, fmt, iter, mem};
 
 use itertools::Itertools as _;
 use once_cell::sync::Lazy;
@@ -77,12 +77,22 @@ pub enum TemplateParseErrorKind {
     SyntaxError,
     #[error("Invalid integer literal")]
     ParseIntError(#[source] ParseIntError),
-    #[error(r#"Keyword "{0}" doesn't exist"#)]
-    NoSuchKeyword(String),
-    #[error(r#"Function "{0}" doesn't exist"#)]
-    NoSuchFunction(String),
+    #[error(r#"Keyword "{name}" doesn't exist"#)]
+    NoSuchKeyword {
+        name: String,
+        candidates: Vec<String>,
+    },
+    #[error(r#"Function "{name}" doesn't exist"#)]
+    NoSuchFunction {
+        name: String,
+        candidates: Vec<String>,
+    },
     #[error(r#"Method "{name}" doesn't exist for type "{type_name}""#)]
-    NoSuchMethod { type_name: String, name: String },
+    NoSuchMethod {
+        type_name: String,
+        name: String,
+        candidates: Vec<String>,
+    },
     #[error(r#"Function "{name}": {message}"#)]
     InvalidArguments { name: String, message: String },
     #[error("Redefinition of function parameter")]
@@ -126,22 +136,27 @@ impl TemplateParseError {
         }
     }
 
-    pub fn no_such_keyword(name: impl Into<String>, span: pest::Span<'_>) -> Self {
-        TemplateParseError::with_span(TemplateParseErrorKind::NoSuchKeyword(name.into()), span)
-    }
-
-    pub fn no_such_function(function: &FunctionCallNode) -> Self {
+    // TODO: migrate callers to something like lookup_method()
+    pub(crate) fn no_such_function(function: &FunctionCallNode) -> Self {
         TemplateParseError::with_span(
-            TemplateParseErrorKind::NoSuchFunction(function.name.to_owned()),
+            TemplateParseErrorKind::NoSuchFunction {
+                name: function.name.to_owned(),
+                candidates: vec![],
+            },
             function.name_span,
         )
     }
 
-    pub fn no_such_method(type_name: impl Into<String>, function: &FunctionCallNode) -> Self {
+    // TODO: migrate all callers to table-based lookup_method()
+    pub(crate) fn no_such_method(
+        type_name: impl Into<String>,
+        function: &FunctionCallNode,
+    ) -> Self {
         TemplateParseError::with_span(
             TemplateParseErrorKind::NoSuchMethod {
                 type_name: type_name.into(),
                 name: function.name.to_owned(),
+                candidates: vec![],
             },
             function.name_span,
         )
@@ -177,6 +192,26 @@ impl TemplateParseError {
         )
     }
 
+    /// If this is a `NoSuchKeyword` error, expands the candidates list with the
+    /// given `other_keywords`.
+    pub fn extend_keyword_candidates<I>(mut self, other_keywords: I) -> Self
+    where
+        I: IntoIterator,
+        I::Item: AsRef<str>,
+    {
+        if let TemplateParseErrorKind::NoSuchKeyword { name, candidates } = &mut self.kind {
+            let other_candidates = collect_similar(name, other_keywords);
+            *candidates = itertools::merge(mem::take(candidates), other_candidates)
+                .dedup()
+                .collect();
+        }
+        self
+    }
+
+    pub fn kind(&self) -> &TemplateParseErrorKind {
+        &self.kind
+    }
+
     /// Original parsing error which typically occurred in an alias expression.
     pub fn origin(&self) -> Option<&Self> {
         self.origin.as_deref()
@@ -864,11 +899,35 @@ pub fn lookup_method<'a, V>(
     if let Some(value) = table.get(function.name) {
         Ok(value)
     } else {
-        // TODO: provide typo hint
-        Err(TemplateParseError::no_such_method(type_name, function))
+        let candidates = collect_similar(function.name, table.keys());
+        Err(TemplateParseError::with_span(
+            TemplateParseErrorKind::NoSuchMethod {
+                type_name: type_name.into(),
+                name: function.name.to_owned(),
+                candidates,
+            },
+            function.name_span,
+        ))
     }
 }
 
+// TODO: merge with revset::collect_similar()?
+fn collect_similar<I>(name: &str, candidates: I) -> Vec<String>
+where
+    I: IntoIterator,
+    I::Item: AsRef<str>,
+{
+    candidates
+        .into_iter()
+        .filter(|cand| {
+            // The parameter is borrowed from clap f5540d26
+            strsim::jaro(name, cand.as_ref()) > 0.7
+        })
+        .map(|s| s.as_ref().to_owned())
+        .sorted_unstable()
+        .collect()
+}
+
 #[cfg(test)]
 mod tests {
     use assert_matches::assert_matches;

cli/tests/test_templater.rs

@@ -31,6 +31,64 @@ fn test_templater_parse_error() {
       |
       = expected <EOI>, `++`, `||`, or `&&`
     "###);
+
+    // Typo
+    test_env.add_config(
+        r###"
+    [template-aliases]
+    'format_id(id)' = 'id.sort()'
+    "###,
+    );
+    insta::assert_snapshot!(render_err(r#"conflicts"#), @r###"
+    Error: Failed to parse template:  --> 1:1
+      |
+    1 | conflicts
+      | ^-------^
+      |
+      = Keyword "conflicts" doesn't exist
+    Hint: Did you mean "conflict"?
+    "###);
+    insta::assert_snapshot!(render_err(r#"commit_id.shorter()"#), @r###"
+    Error: Failed to parse template:  --> 1:11
+      |
+    1 | commit_id.shorter()
+      |           ^-----^
+      |
+      = Method "shorter" doesn't exist for type "CommitOrChangeId"
+    Hint: Did you mean "short", "shortest"?
+    "###);
+    insta::assert_snapshot!(render_err(r#"cat()"#), @r###"
+    Error: Failed to parse template:  --> 1:1
+      |
+    1 | cat()
+      | ^-^
+      |
+      = Function "cat" doesn't exist
+    "###);
+    insta::assert_snapshot!(render_err(r#""".lines().map(|s| se)"#), @r###"
+    Error: Failed to parse template:  --> 1:20
+      |
+    1 | "".lines().map(|s| se)
+      |                    ^^
+      |
+      = Keyword "se" doesn't exist
+    Hint: Did you mean "s", "self"?
+    "###);
+    insta::assert_snapshot!(render_err(r#"format_id(commit_id)"#), @r###"
+    Error: Failed to parse template:  --> 1:1
+      |
+    1 | format_id(commit_id)
+      | ^------------------^
+      |
+      = Alias "format_id()" cannot be expanded
+     --> 1:4
+      |
+    1 | id.sort()
+      |    ^--^
+      |
+      = Method "sort" doesn't exist for type "CommitOrChangeId"
+    Hint: Did you mean "short", "shortest"?
+    "###);
 }
 
 #[test]