[C++] Convert initial echo command into ninja description

If the first command for a rule is an echo with no redirections,
strip any outer quotes and use the result as the ninja rule
description.

This makes Android builds much more readable by preventing every
successful rule from writing a single line, allowing ninja to
reuse the current line for its status.

1 files changed, 60 insertions, 1 deletions

diff --git a/ninja.cc b/ninja.cc
index 7ef2bd6..747d959 100644
--- a/ninja.cc
+++ b/ninja.cc
@@ -245,6 +245,60 @@ class NinjaGenerator {
                        cmd_buf_.size() - orig_size);
   }
 
+  bool GetDescriptionFromCommand(StringPiece cmd, string *out) {
+    cmd = TrimSpace(cmd);
+
+    if (!HasPrefix(cmd, "echo ")) {
+      return false;
+    }
+    cmd = cmd.substr(5, cmd.size());
+
+    cmd_buf_.clear();
+    cmd = TranslateCommand(cmd.as_string().c_str());
+
+    bool prev_backslash = false;
+    char quote = 0;
+    string out_buf;
+
+    // Strip outer quotes, and fail if it is not a single echo command
+    for (StringPiece::iterator in = cmd.begin(); in != cmd.end(); in++) {
+      if (prev_backslash) {
+        prev_backslash = false;
+        out_buf += *in;
+      } else if (*in == '\\') {
+        prev_backslash = true;
+        out_buf += *in;
+      } else if (quote) {
+        if (*in == quote) {
+          quote = 0;
+        } else {
+          out_buf += *in;
+        }
+      } else {
+        switch (*in) {
+        case '\'':
+        case '"':
+        case '`':
+          quote = *in;
+          break;
+
+        case '<':
+        case '>':
+        case '&':
+        case '|':
+        case ';':
+          return false;
+
+        default:
+          out_buf += *in;
+        }
+      }
+    }
+
+    *out = out_buf;
+    return true;
+  }
+
   bool GenShellScript(const vector<Command*>& commands) {
     bool use_gomacc = false;
     bool should_ignore_error = false;
@@ -331,7 +385,12 @@ class NinjaGenerator {
     if (!commands.empty()) {
       rule_name = GenRuleName();
       fprintf(fp_, "rule %s\n", rule_name.c_str());
-      fprintf(fp_, " description = build $out\n");
+
+      string description = "build $out";
+      if (GetDescriptionFromCommand(*(commands[0]->cmd), &description)) {
+        commands[0]->cmd->assign("true");
+      }
+      fprintf(fp_, " description = %s\n", description.c_str());
 
       use_local_pool |= GenShellScript(commands);
       EmitDepfile();