Fix RDF parsing of class members confused for existing columns

Author: prakharsing7

tree/dataframe/src/RDFInterfaceUtils.cxx

@@ -106,6 +106,12 @@ std::pair<ColumnNames_t, ColumnNames_t> FindUsedColsAndAliases(const std::string
          // token is not a potential variable name, skip it
          continue;
       }
+      // Skip symbols that are member accesses (obj.method) — they are not column references.
+      // lexertk does not produce dot-prefixed tokens, so the token immediately before a method
+      // name is always the literal "." token when it is a member access.
+      if (i > 0 && tokens[i - 1].value == ".") {
+         continue;
+      }
 
       ColumnNames_t potentialColNames({tok.value});
 
@@ -159,7 +165,7 @@ TString ResolveAliases(const TString &expr, const ColumnNames_t &usedAliases,
 
    for (const auto &alias : usedAliases) {
       const auto &col = colRegister.ResolveAlias(alias);
-      TPRegexp replacer("\\b" + EscapeDots(alias) + "\\b");
+      TPRegexp replacer("(?<!\\.)\\b" + EscapeDots(alias) + "\\b");
       replacer.Substitute(out, col.data(), "g");
    }
 
@@ -200,7 +206,7 @@ ParsedExpression ParseRDFExpression(std::string_view expr, const ROOT::Internal:
              [](const std::string &a, const std::string &b) { return a.size() > b.size(); });
    for (const auto &col : usedCols) {
       const auto varIdx = std::distance(usedCols.begin(), std::find(usedCols.begin(), usedCols.end(), col));
-      TPRegexp replacer("\\b" + EscapeDots(col) + "\\b");
+      TPRegexp replacer("(?<!\\.)\\b" + EscapeDots(col) + "\\b");
       replacer.Substitute(exprWithVars, varNames[varIdx], "g");
    }
 

tree/dataframe/test/dataframe_colnames.cxx

@@ -1,4 +1,5 @@
 #include "ROOT/RDataFrame.hxx"
+#include <TInterpreter.h>
 #include <TTree.h>
 
 #include "gtest/gtest.h"
@@ -89,3 +90,56 @@ TEST(Aliases, FilterOnAliasJit)
    auto c = tdf.Define("c0", [&i]() { return i++; }).Alias("c1", "c0").Filter("c1>1").Count();
    EXPECT_EQ(1U, *c);
 }
+
+// Regression test for https://github.com/root-project/root/issues/22295
+// A column named "phi" must not be confused with a .phi() method call in a JIT expression.
+TEST(ColNames, MethodCallNotConfusedWithColumn)
+{
+   // Declare minimal helper types for use in JIT strings.
+   // Using gInterpreter::Declare avoids any dependency on GenVector or other libraries.
+   gInterpreter->Declare("struct RDF22295Vec { double phi() const { return 42.0; } };");
+   gInterpreter->Declare("struct RDF22295Mem { double phi = 1.5; };");
+
+   // Case 1: column "phi" exists, expression calls .phi() method — must not throw,
+   // and the result must be the value returned by the method (42.0), not a substitution
+   // artifact. Before the fix this crashed with "no member named 'var0'" because the
+   // parser replaced .phi() with .var0().
+   {
+      ROOT::RDataFrame df(1);
+      auto df2 = df.Define("phi", "1.0");
+      std::vector<double> v;
+      EXPECT_NO_THROW({
+         auto df3 = df2.Define("result", "RDF22295Vec{}.phi()");
+         v = *df3.Take<double>("result");
+      });
+      EXPECT_NEAR(42.0, v[0], 1e-9);
+   }
+
+   // Case 2: column "phi" exists, expression uses BOTH .phi() method call AND standalone
+   // phi column reference — only the standalone reference must be substituted.
+   {
+      ROOT::RDataFrame df(1);
+      auto df2 = df.Define("phi", "0.5");
+      std::vector<double> v;
+      EXPECT_NO_THROW({
+         auto df3 = df2.Define("result", "RDF22295Vec{}.phi() + phi");
+         v = *df3.Take<double>("result");
+      });
+      // .phi() returns 42.0; standalone phi column = 0.5
+      EXPECT_NEAR(42.5, v[0], 1e-9);
+   }
+
+   // Case 3: data-member access obj.phi (not a function call) must still work after the
+   // fix — the preceding-dot guard must not break legitimate dot-chain expressions.
+   {
+      ROOT::RDataFrame df(1);
+      auto df2 = df.Define("phi", "0.5");
+      std::vector<double> v;
+      EXPECT_NO_THROW({
+         auto df3 = df2.Define("result", "RDF22295Mem{}.phi + phi");
+         v = *df3.Take<double>("result");
+      });
+      // data member .phi = 1.5; standalone phi column = 0.5
+      EXPECT_NEAR(2.0, v[0], 1e-9);
+   }
+}