Add trim_multiline utility (fixes #139)

src/collapsible_if.rs

@@ -18,7 +18,7 @@ use rustc::middle::def::*;
 use syntax::ast::*;
 use syntax::ptr::P;
 use syntax::codemap::{Span, Spanned, ExpnInfo};
-use utils::{in_macro, span_help_and_lint, snippet};
+use utils::{in_macro, span_help_and_lint, snippet, snippet_block};
 
 declare_lint! {
     pub COLLAPSIBLE_IF,
@@ -55,7 +55,7 @@ fn check_expr_expd(cx: &Context, e: &Expr, info: Option<&ExpnInfo>) {
                     "this if statement can be collapsed",
                     &format!("try\nif {} && {} {}",
                              check_to_string(cx, check), check_to_string(cx, check_inner),
-                             snippet(cx, content.span, "..")));
+                             snippet_block(cx, content.span, "..")));
             }
     }
 }

src/lib.rs

@@ -1,5 +1,6 @@
 #![feature(plugin_registrar, box_syntax)]
 #![feature(rustc_private, collections)]
+#![feature(str_split_at)]
 #![allow(unused_imports, unknown_lints)]
 
 #[macro_use]

src/misc.rs

@@ -7,7 +7,7 @@ use rustc::lint::{Context, LintPass, LintArray, Lint, Level};
 use rustc::middle::ty;
 use syntax::codemap::{Span, Spanned};
 
-use utils::{match_path, snippet, span_lint, span_help_and_lint, walk_ptrs_ty};
+use utils::{match_path, snippet, snippet_block, span_lint, span_help_and_lint, walk_ptrs_ty};
 
 /// Handles uncategorized lints
 /// Currently handles linting of if-let-able matches
@@ -37,7 +37,7 @@ impl LintPass for MiscPass {
                     // an enum is extended. So we only consider cases where a `_` wildcard is used
                     if arms[1].pats[0].node == PatWild(PatWildSingle) &&
                             arms[0].pats.len() == 1 {
-                        let body_code = snippet(cx, arms[0].body.span, "..");
+                        let body_code = snippet_block(cx, arms[0].body.span, "..");
                         let suggestion = if let ExprBlock(_) = arms[0].body.node {
                             body_code.into_owned()
                         } else {

src/utils.rs

@@ -51,6 +51,35 @@ pub fn snippet<'a>(cx: &Context, span: Span, default: &'a str) -> Cow<'a, str> {
     cx.sess().codemap().span_to_snippet(span).map(From::from).unwrap_or(Cow::Borrowed(default))
 }
 
+/// convert a span (from a block) to a code snippet if available, otherwise use default, e.g.
+/// `snippet(cx, expr.span, "..")`
+/// This trims the code of indentation, except for the first line
+/// Use it for blocks or block-like things which need to be printed as such
+pub fn snippet_block<'a>(cx: &Context, span: Span, default: &'a str) -> Cow<'a, str> {
+    let snip = snippet(cx, span, default);
+    trim_multiline(snip, true)
+}
+
+/// Trim indentation from a multiline string
+/// with possibility of ignoring the first line
+pub fn trim_multiline<'a>(s: Cow<'a, str>, ignore_first: bool) -> Cow<'a, str> {
+    let x = s.lines().skip(ignore_first as usize)
+             .map(|l| l.char_indices()
+                       .find(|&(_,x)| x != ' ')
+                       .unwrap_or((l.len(),' ')).0)
+             .min().unwrap_or(0);
+    if x > 0 {
+        Cow::Owned(s.lines().enumerate().map(|(i,l)| if ignore_first && i==0 {
+                                                        l
+                                                     } else {
+                                                        l.split_at(x).1
+                                                     }).collect::<Vec<_>>()
+                                       .join("\n"))
+    } else {
+        s
+    }
+}
+
 /// get a parent expr if any – this is useful to constrain a lint
 pub fn get_parent_expr<'c>(cx: &'c Context, e: &Expr) -> Option<&'c Expr> {
     let map = &cx.tcx.map;