sgrep: Install syntactic code search tool as an external linter.

Add sgrep (sgrep.dev) to tooling and include simple rule as
proof of concept. Included rule detects use of old django render
function.

Also added a rule that looks for if-else statements where both
code paths are identical.

tools/lib/provision.py

@@ -385,6 +385,9 @@ def main(options):
     # Install shellcheck.
     run_as_root(["tools/setup/install-shellcheck"])
 
+    # Install sgrep.
+    run_as_root(["tools/setup/install-sgrep"])
+
     setup_venvs.main()
 
     run_as_root(["cp", REPO_STOPWORDS_PATH, TSEARCH_STOPWORDS_PATH])

tools/lint

@@ -92,6 +92,11 @@ def run():
                                   description="Checks commit messages for common formatting errors."
                                   "(config: .gitlint)")
 
+    sgrep_command = ["sgrep-lint", "--config=./tools/sgrep.yml", "--error"]
+    linter_config.external_linter('sgrep-py', [*sgrep_command, "--lang=python"], ['py'],
+                                  description="Syntactic Grep (sgrep) Code Search Tool "
+                                  "(config: ./tools/sgrep.yml)")
+
     @linter_config.lint
     def custom_py():
         # type: () -> int

tools/linter_lib/custom_check.py

@@ -415,9 +415,6 @@ python_rules = RuleList(
          'description': "Don't use datetime in backend code.\n"
          "See https://zulip.readthedocs.io/en/latest/contributing/code-style.html#naive-datetime-objects",
          },
-        {'pattern': r'render_to_response\(',
-         'description': "Use render() instead of render_to_response().",
-         },
         {'pattern': 'from os.path',
          'description': "Don't use from when importing from the standard library",
          },

tools/setup/install-sgrep

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -e
+
+version=0.4.9b5
+tarball=sgrep-$version-ubuntu-16.04.tgz
+sha256=9e57323fd0eb9133b7ff301a6be8361c073c3bfe6e6959ca1b622e5abc176e03
+tarball_url=https://github.com/returntocorp/sgrep/releases/download/v$version/$tarball
+
+if ! out="$(sgrep-lint --version 2>/dev/null)" || [[ "$out" != "$version" ]]
+then
+    tmpdir="$(mktemp -d)"
+    trap 'rm -r "$tmpdir"' EXIT
+    cd "$tmpdir"
+    wget -nv "$tarball_url"
+    sha256sum -c <<< "$sha256  $tarball"
+    tar -xzf "$tarball" -C /usr/local/lib/
+    ln -sf /usr/local/lib/sgrep-lint-files/sgrep-lint /usr/local/bin/sgrep-lint
+    ln -sf /usr/local/lib/sgrep-lint-files/sgrep /usr/local/bin/sgrep
+fi

tools/sgrep.yml

@@ -0,0 +1,18 @@
+# See https://github.com/returntocorp/sgrep/blob/develop/docs/config.md for sgrep rule format
+
+rules:
+  - id: deprecated-render-usage
+    pattern: django.shortcuts.render_to_response(...)
+    message: Use render() (from django.shortcuts) instead of render_to_response()
+    languages: [python]
+    severity: ERROR
+  - id: useless-if-body
+    patterns:
+        - pattern: |
+            if $X:
+                $S
+            else:
+                $S
+    message: "useless if statment; both blocks have the same body"
+    languages: [python]
+    severity: ERROR

version.py

@@ -34,4 +34,4 @@ DESKTOP_WARNING_VERSION = "5.0.0"
 #   historical commits sharing the same major version, in which case a
 #   minor version bump suffices.
 
-PROVISION_VERSION = '75.5'
+PROVISION_VERSION = '75.6'