Consider actual indentation of previous line for smart indent

book/src/configuration.md

@@ -65,6 +65,7 @@ Its settings will be merged with the configuration directory `config.toml` and t
 | `workspace-lsp-roots` | Directories relative to the workspace root that are treated as LSP roots. Should only be set in `.helix/config.toml` | `[]` |
 | `default-line-ending` | The line ending to use for new documents. Can be `native`, `lf`, `crlf`, `ff`, `cr` or `nel`. `native` uses the platform's native line ending (`crlf` on Windows, otherwise `lf`). | `native` |
 | `insert-final-newline` | Whether to automatically insert a trailing line-ending on write if missing | `true` |
+| `indent-heuristic` | How the indentation for a newly inserted line is computed: `simple` just copies the indentation level from the previous line, `tree-sitter` computes the indentation based on the syntax tree and `hybrid` combines both approaches. If the chosen heuristic is not available, a different one will be used as a fallback (the fallback order being `hybrid` -> `tree-sitter` -> `simple`). | `hybrid`
 
 ### `[editor.statusline]` Section
 

book/src/guides/indent.md

@@ -12,6 +12,15 @@ Note that it matters where these added indents begin. For example,
 multiple indent level increases that start on the same line only increase
 the total indent level by 1. See [Capture types](#capture-types).
 
+By default, Helix uses the `hybrid` indentation heuristic. This means that
+indent queries are not used to compute the expected absolute indentation of a
+line but rather the expected difference in indentation between the new and an
+already existing line. This difference is then added to the actual indentation
+of the already existing line. Since this makes errors in the indent queries
+harder to find, it is recommended to disable it when testing via
+`:set indent-heuristic tree-sitter`. The rest of this guide assumes that
+the `tree-sitter` heuristic is used.
+
 ## Indent queries
 
 When Helix is inserting a new line through `o`, `O`, or `<ret>`, to determine

helix-core/src/syntax.rs

@@ -442,6 +442,22 @@ pub struct IndentationConfiguration {
     pub unit: String,
 }
 
+/// How the indentation for a newly inserted line should be determined.
+/// If the selected heuristic is not available (e.g. because the current
+/// language has no tree-sitter indent queries), a simpler one will be used.
+#[derive(Debug, Default, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum IndentationHeuristic {
+    /// Just copy the indentation of the line that the cursor is currently on.
+    Simple,
+    /// Use tree-sitter indent queries to compute the expected absolute indentation level of the new line.
+    TreeSitter,
+    /// Use tree-sitter indent queries to compute the expected difference in indentation between the new line
+    /// and the line before. Add this to the actual indentation level of the line before.
+    #[default]
+    Hybrid,
+}
+
 /// Configuration for auto pairs
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "kebab-case", deny_unknown_fields, untagged)]

helix-core/tests/indent.rs

@@ -210,15 +210,15 @@ fn test_treesitter_indent(
             let suggested_indent = treesitter_indent_for_pos(
                 indent_query,
                 &syntax,
-                &indent_style,
                 tab_width,
                 indent_style.indent_width(tab_width),
                 text,
                 i,
                 text.line_to_char(i) + pos,
                 false,
             )
-            .unwrap();
+            .unwrap()
+            .to_string(&indent_style, tab_width);
             assert!(
                 line.get_slice(..pos).map_or(false, |s| s == suggested_indent),
                 "Wrong indentation for file {:?} on line {}:\n\"{}\" (original line)\n\"{}\" (suggested indentation)\n",

helix-term/src/commands.rs

@@ -3053,6 +3053,7 @@ fn insert_with_indent(cx: &mut Context, cursor_fallback: IndentFallbackPos) {
             let indent = indent::indent_for_newline(
                 language_config,
                 syntax,
+                &doc.config.load().indent_heuristic,
                 &doc.indent_style,
                 tab_width,
                 text,
@@ -3181,6 +3182,7 @@ fn open(cx: &mut Context, open: Open) {
         let indent = indent::indent_for_newline(
             doc.language_config(),
             doc.syntax(),
+            &doc.config.load().indent_heuristic,
             &doc.indent_style,
             doc.tab_width(),
             text,
@@ -3720,6 +3722,7 @@ pub mod insert {
                 let indent = indent::indent_for_newline(
                     doc.language_config(),
                     doc.syntax(),
+                    &doc.config.load().indent_heuristic,
                     &doc.indent_style,
                     doc.tab_width(),
                     text,

helix-view/src/editor.rs

@@ -42,7 +42,7 @@ use anyhow::{anyhow, bail, Error};
 pub use helix_core::diagnostic::Severity;
 use helix_core::{
     auto_pairs::AutoPairs,
-    syntax::{self, AutoPairConfig, SoftWrap},
+    syntax::{self, AutoPairConfig, IndentationHeuristic, SoftWrap},
     Change, LineEnding, NATIVE_LINE_ENDING,
 };
 use helix_core::{Position, Selection};
@@ -291,6 +291,9 @@ pub struct Config {
     pub insert_final_newline: bool,
     /// Enables smart tab
     pub smart_tab: Option<SmartTabConfig>,
+    /// Which indent heuristic to use when a new line is inserted
+    #[serde(default)]
+    pub indent_heuristic: IndentationHeuristic,
 }
 
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize, Eq, PartialOrd, Ord)]
@@ -841,6 +844,7 @@ impl Default for Config {
             default_line_ending: LineEndingConfig::default(),
             insert_final_newline: true,
             smart_tab: Some(SmartTabConfig::default()),
+            indent_heuristic: IndentationHeuristic::default(),
         }
     }
 }

runtime/queries/c/indents.scm

@@ -36,3 +36,16 @@
 (parameter_list
   . (parameter_declaration) @anchor
   (#set! "scope" "tail")) @align
+(argument_list
+  . (_) @anchor
+  (#set! "scope" "tail")) @align
+; These are a bit opinionated since some people just indent binary/ternary expressions spanning multiple lines.
+; Since they are only triggered when a newline is inserted into an already complete binary/ternary expression,
+; this should happen rarely, so it is not a big deal either way.
+; Additionally, adding these queries has the advantage of preventing such continuation lines from being used
+; as the baseline when the `hybrid` indent heuristic is used (which is desirable since their indentation is so inconsistent). 
+(binary_expression
+  (#set! "scope" "tail")) @anchor @align
+(conditional_expression
+  "?" @anchor
+  (#set! "scope" "tail")) @align