Language Server: textDocument/signatureHelp

Implements a pretty barebones function signature help mechanism in
the language server.

Users can use `Analysis::resolve_callback()` to get basic information
about a call site.

Fixes #102

1 files changed, 55 insertions, 1 deletions

diff --git a/crates/ra_analysis/src/descriptors.rs b/crates/ra_analysis/src/descriptors.rs
index 0731b5572..4dcac1aa2 100644
--- a/crates/ra_analysis/src/descriptors.rs
+++ b/crates/ra_analysis/src/descriptors.rs
@@ -4,7 +4,8 @@ use std::{
 use relative_path::RelativePathBuf;
 use ra_syntax::{
     SmolStr,
-    ast::{self, NameOwner},
+    ast::{self, NameOwner, AstNode, TypeParamsOwner},
+    text_utils::is_subrange
 };
 use {
     FileId,
@@ -218,3 +219,56 @@ fn resolve_submodule(
     }
     (points_to, problem)
 }
+
+#[derive(Debug, Clone)]
+pub struct FnDescriptor {
+    pub name: Option<String>,
+    pub label : String,
+    pub ret_type: Option<String>,
+    pub params: Vec<String>,
+}
+
+impl FnDescriptor {
+    pub fn new(node: ast::FnDef) -> Self {
+        let name = node.name().map(|name| name.text().to_string());
+
+        // Strip the body out for the label.
+        let label : String = if let Some(body) = node.body() {
+            let body_range = body.syntax().range();
+            let label : String = node.syntax().children()
+                .filter(|child| !is_subrange(body_range, child.range()))
+                .map(|node| node.text().to_string())
+                .collect();
+            label
+        } else {
+            node.syntax().text().to_string()
+        };
+
+        let params = FnDescriptor::param_list(node);
+        let ret_type = node.ret_type().map(|r| r.syntax().text().to_string());
+
+        FnDescriptor {
+            name,
+            ret_type,
+            params,
+            label
+        }
+    }
+
+    fn param_list(node: ast::FnDef) -> Vec<String> {
+        let mut res = vec![];
+        if let Some(param_list) = node.param_list() {
+            if let Some(self_param) = param_list.self_param() {
+                res.push(self_param.syntax().text().to_string())
+            }
+
+            // Maybe use param.pat here? See if we can just extract the name?
+            //res.extend(param_list.params().map(|p| p.syntax().text().to_string()));
+            res.extend(param_list.params()
+                .filter_map(|p| p.pat())
+                .map(|pat| pat.syntax().text().to_string())
+            );
+        }
+        res
+    }
+}
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