Doc comments

doc/manual/rl-next/repl-doc-renders-doc-comments.md

@@ -0,0 +1,53 @@
+---
+synopsis: "`nix-repl`'s `:doc` shows documentation comments"
+significance: significant
+issues:
+- 3904
+- 10771
+prs:
+- 1652
+- 9054
+- 11072
+---
+
+`nix repl` has a `:doc` command that previously only rendered documentation for internally defined functions.
+This feature has been extended to also render function documentation comments, in accordance with [RFC 145].
+
+Example:
+
+```
+nix-repl> :doc lib.toFunction
+Function toFunction
+    … defined at /home/user/h/nixpkgs/lib/trivial.nix:1072:5
+
+    Turns any non-callable values into constant functions. Returns
+    callable values as is.
+
+Inputs
+
+    v
+
+      : Any value
+
+Examples
+
+    :::{.example}
+
+## lib.trivial.toFunction usage example
+
+      | nix-repl> lib.toFunction 1 2
+      | 1
+      | 
+      | nix-repl> lib.toFunction (x: x + 1) 2
+      | 3
+
+    :::
+```
+
+Known limitations:
+- It does not render documentation for "formals", such as `{ /** the value to return */ x, ... }: x`.
+- Some extensions to markdown are not yet supported, as you can see in the example above.
+
+We'd like to acknowledge Yingchi Long for proposing a proof of concept for this functionality in [#9054](https://github.com/NixOS/nix/pull/9054), as well as @sternenseemann and Johannes Kirschbauer for their contributions, proposals, and their work on [RFC 145].
+
+[RFC 145]: https://github.com/NixOS/rfcs/pull/145

doc/manual/src/contributing/testing.md

@@ -91,7 +91,7 @@ A environment variables that Google Test accepts are also worth knowing:
 Putting the two together, one might run
 
 ```bash
-GTEST_BREIF=1 GTEST_FILTER='ErrorTraceTest.*' meson test nix-expr-tests -v
+GTEST_BRIEF=1 GTEST_FILTER='ErrorTraceTest.*' meson test nix-expr-tests -v
 ```
 
 for short but comprensive output.

src/libcmd/repl-interacter.cc

@@ -73,7 +73,7 @@ static int listPossibleCallback(char * s, char *** avp)
 {
     auto possible = curRepl->completePrefix(s);
 
-    if (possible.size() > (INT_MAX / sizeof(char *)))
+    if (possible.size() > (std::numeric_limits<int>::max() / sizeof(char *)))
         throw Error("too many completions");
 
     int ac = 0;

src/libcmd/repl.cc

@@ -27,6 +27,7 @@
 #include "local-fs-store.hh"
 #include "print.hh"
 #include "ref.hh"
+#include "value.hh"
 
 #if HAVE_BOEHMGC
 #define GC_INCLUDE_NEW
@@ -616,6 +617,38 @@ ProcessLineResult NixRepl::processLine(std::string line)
 
     else if (command == ":doc") {
         Value v;
+
+        auto expr = parseString(arg);
+        std::string fallbackName;
+        PosIdx fallbackPos;
+        DocComment fallbackDoc;
+        if (auto select = dynamic_cast<ExprSelect *>(expr)) {
+            Value vAttrs;
+            auto name = select->evalExceptFinalSelect(*state, *env, vAttrs);
+            fallbackName = state->symbols[name];
+
+            state->forceAttrs(vAttrs, noPos, "while evaluating an attribute set to look for documentation");
+            auto attrs = vAttrs.attrs();
+            assert(attrs);
+            auto attr = attrs->get(name);
+            if (!attr) {
+                // When missing, trigger the normal exception
+                // e.g. :doc builtins.foo
+                // behaves like
+                // nix-repl> builtins.foo      
+                // error: attribute 'foo' missing
+                evalString(arg, v);
+                assert(false);
+            }
+            if (attr->pos) {
+                fallbackPos = attr->pos;
+                fallbackDoc = state->getDocCommentForPos(fallbackPos);
+            }
+
+        } else {
+            evalString(arg, v);
+        }
+
         evalString(arg, v);
         if (auto doc = state->getDoc(v)) {
             std::string markdown;
@@ -633,6 +666,19 @@ ProcessLineResult NixRepl::processLine(std::string line)
             markdown += stripIndentation(doc->doc);
 
             logger->cout(trim(renderMarkdownToTerminal(markdown)));
+        } else if (fallbackPos) {
+            std::stringstream ss;
+            ss << "Attribute `" << fallbackName << "`\n\n";
+            ss << "  … defined at " << state->positions[fallbackPos] << "\n\n";
+            if (fallbackDoc) {
+                ss << fallbackDoc.getInnerText(state->positions);
+            } else {
+                ss << "No documentation found.\n\n";
+            }
+
+            auto markdown = ss.str();
+            logger->cout(trim(renderMarkdownToTerminal(markdown)));
+
         } else
             throw Error("value does not have documentation");
     }

src/libexpr/eval.cc

@@ -559,6 +559,54 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
                 .doc = doc,
             };
     }
+    if (v.isLambda()) {
+        auto exprLambda = v.payload.lambda.fun;
+
+        std::stringstream s(std::ios_base::out);
+        std::string name;
+        auto pos = positions[exprLambda->getPos()];
+        std::string docStr;
+
+        if (exprLambda->name) {
+            name = symbols[exprLambda->name];
+        }
+
+        if (exprLambda->docComment) {
+            docStr = exprLambda->docComment.getInnerText(positions);
+        }
+
+        if (name.empty()) {
+            s << "Function ";
+        }
+        else {
+            s << "Function `" << name << "`";
+            if (pos)
+                s << "\\\n  … " ;
+            else
+                s << "\\\n";
+        }
+        if (pos) {
+            s << "defined at " << pos;
+        }
+        if (!docStr.empty()) {
+            s << "\n\n";
+        }
+
+        s << docStr;
+
+        s << '\0'; // for making a c string below
+        std::string ss = s.str();
+
+        return Doc {
+            .pos = pos,
+            .name = name,
+            .arity = 0, // FIXME: figure out how deep by syntax only? It's not semantically useful though...
+            .args = {},
+            .doc =
+                // FIXME: this leaks; make the field std::string?
+                strdup(ss.data()),
+        };
+    }
     return {};
 }
 
@@ -1367,6 +1415,22 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
     v = *vAttrs;
 }
 
+Symbol ExprSelect::evalExceptFinalSelect(EvalState & state, Env & env, Value & attrs)
+{
+    Value vTmp;
+    Symbol name = getName(attrPath[attrPath.size() - 1], state, env);
+
+    if (attrPath.size() == 1) {
+        e->eval(state, env, vTmp);
+    } else {
+        ExprSelect init(*this);
+        init.attrPath.pop_back();
+        init.eval(state, env, vTmp);
+    }
+    attrs = vTmp;
+    return name;
+}
+
 
 void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
 {
@@ -2828,13 +2892,37 @@ Expr * EvalState::parse(
     const SourcePath & basePath,
     std::shared_ptr<StaticEnv> & staticEnv)
 {
-    auto result = parseExprFromBuf(text, length, origin, basePath, symbols, settings, positions, rootFS, exprSymbols);
+    DocCommentMap tmpDocComments; // Only used when not origin is not a SourcePath
+    DocCommentMap *docComments = &tmpDocComments;
+
+    if (auto sourcePath = std::get_if<SourcePath>(&origin)) {
+        auto [it, _] = positionToDocComment.try_emplace(*sourcePath);
+        docComments = &it->second;
+    }
+
+    auto result = parseExprFromBuf(text, length, origin, basePath, symbols, settings, positions, *docComments, rootFS, exprSymbols);
 
     result->bindVars(*this, staticEnv);
 
     return result;
 }
 
+DocComment EvalState::getDocCommentForPos(PosIdx pos)
+{
+    auto pos2 = positions[pos];
+    auto path = pos2.getSourcePath();
+    if (!path)
+        return {};
+
+    auto table = positionToDocComment.find(*path);
+    if (table == positionToDocComment.end())
+        return {};
+
+    auto it = table->second.find(pos);
+    if (it == table->second.end())
+        return {};
+    return it->second;
+}
 
 std::string ExternalValueBase::coerceToString(EvalState & state, const PosIdx & pos, NixStringContext & context, bool copyMore, bool copyToStore) const
 {

src/libexpr/eval.hh

@@ -130,6 +130,8 @@ struct Constant
     typedef std::map<std::string, Value *> ValMap;
 #endif
 
+typedef std::map<PosIdx, DocComment> DocCommentMap;
+
 struct Env
 {
     Env * up;
@@ -329,6 +331,12 @@ private:
 #endif
     FileEvalCache fileEvalCache;
 
+    /**
+     * Associate source positions of certain AST nodes with their preceding doc comment, if they have one.
+     * Grouped by file.
+     */
+    std::map<SourcePath, DocCommentMap> positionToDocComment;
+
     LookupPath lookupPath;
 
     std::map<std::string, std::optional<std::string>> lookupPathResolved;
@@ -771,6 +779,8 @@ public:
         std::string_view pathArg,
         PosIdx pos);
 
+    DocComment getDocCommentForPos(PosIdx pos);
+
 private:
 
     /**

src/libexpr/lexer-helpers.cc

@@ -0,0 +1,30 @@
+#include "lexer-tab.hh"
+#include "lexer-helpers.hh"
+#include "parser-tab.hh"
+
+void nix::lexer::internal::initLoc(YYLTYPE * loc)
+{
+    loc->beginOffset = loc->endOffset = 0;
+}
+
+void nix::lexer::internal::adjustLoc(yyscan_t yyscanner, YYLTYPE * loc, const char * s, size_t len)
+{
+    loc->stash();
+
+    LexerState & lexerState = *yyget_extra(yyscanner);
+
+    if (lexerState.docCommentDistance == 1) {
+        // Preceding token was a doc comment.
+        ParserLocation doc;
+        doc.beginOffset = lexerState.lastDocCommentLoc.beginOffset;
+        ParserLocation docEnd;
+        docEnd.beginOffset = lexerState.lastDocCommentLoc.endOffset;
+        DocComment docComment{lexerState.at(doc), lexerState.at(docEnd)};
+        PosIdx locPos = lexerState.at(*loc);
+        lexerState.positionToDocComment.emplace(locPos, docComment);
+    }
+    lexerState.docCommentDistance++;
+
+    loc->beginOffset = loc->endOffset;
+    loc->endOffset += len;
+}

src/libexpr/lexer-helpers.hh

@@ -0,0 +1,9 @@
+#pragma once
+
+namespace nix::lexer::internal {
+
+void initLoc(YYLTYPE * loc);
+
+void adjustLoc(yyscan_t yyscanner, YYLTYPE * loc, const char * s, size_t len);
+
+} // namespace nix::lexer